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Argonne National Laboralor\'. \_ ;lh fao;lilies in lh_;'sl;ilcs of lllinoi.,, and Idaho. isowned by tile United States govcFnnl{nl, and op{r;.ilcd b\' The I.'ni\'crsil\ (.HChicagtiunder the provisit+n.,; t,l a conlracl with the l)cparii+_cill of lt;icig)'.
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Status Report on the Advanced Photon Source, Spring 1990David E. Moncton .................................................................................. 7
Opportunities for Atomic Physics with Hard Synchrotron RadiationBernd Crasemann .............................................................................. 12
New Frontiers in X-Ray Photoionization of Ions and AtomsSteven T. Manson ................................................................................ 38
The Advanced Light Source: A New 1.5-GEV Synchrotron RadiationFacility at the Lawrence Berkeley Laboratory
Alfred S. Schlachter ............................................................................ 59
The RIKEN - JAERI 8-GEV Synchrotron Radiation Project - SPring - 8Yohko Awaya .................................................................................... 123
Photoionization of Ions and the General Program in Atomic and MolecularPhysics at Daresbury
John B. West ..................................................................................... 144
Research with Stored Multi-Charged Ions at the APS and the NSLSDavid A. Church ............................................................................... 148
Thoughts on Future ESSR Studies of Inner Core LevelsManfred O. Krause ............................................................................ 183
Beam-Line Considerations for Experiments with Highly-Charged Ions1 Brant M. Johnson ............................................................................... 200
Spectral Characteristics of Insertion Device Sources at the AdvancedPhoton Source
P. James Viccaro ................................................................................ 227
!
iii
CONTENTS (Cont'd)
Can a Powerfill Source (APS) Cast Useful Light on Atomic Hole StateProcesses?
Paul L. Cowan ................................................................................... 272i
Studies of Free and Deposited Clusters Using Syachrotron RadiationWolfgang Eberhardt ........................................................................... 290
Atomic Physic_ with New Synchrotron Radiation: Report from theJapanese Working Group
Masahiro Kimura. .......................... 298
Argon - Ion Charge Distributions Following Near - Threshold IonizationJ on C. Levin ....................................................................................... 318
The Workshop on Atomic Physics at the Advanced Photon Source was jointlysponsored by the Physics Division, the Advanced Photon Source, and the Divisionof Educational Programs at Argonne National Laboratory. The workshoporganizers wish to express their thanks to the sponsors for making this meetingpossible, and to ali invited speakers for sharing their research interests and theirinsights. [['hanks also go to Bonnie Meyer and Susan Pi_ 'loglou of the AdvancedPhoton Source and Joan Brunsvold of the Office of Public Affairs for their valuableassistance.
Program and Organiz, ing Committee
WORKSHOP ON ATOMIC PHYSICS AT THE ADVANCED PHOTON SOURCE
ABSTRACT
The first Workshop on Atomic Physics at the Advanced Photon Source was held atArgonne National Laboratory on March 29-30, 1990. The unprecedentedbrightness of the Advanced Photon Source (APS) in the hard X..ray region isexpected to make possible a vast array of new research opportunities for theatomic physics community. Starting with discussions of the history and currentstatus of the field, presentations were made on various future directions tbrresearch with hard X-rays interacting with atoms, ions, clusters, and solids.Also important were the discussions on the design and status of the four next-generation rings coming on line during the 1990's: the ALS 1.6-GEV ring atBerleley; the ESRF 6.0-GEV ring at Grenoble (1993); the APS 7.0-GEV ring atArgonne (1995); and the SPring-8 8.0-GEV ring in Japan (1998). The participationof more than one hundred scientists from domestic as well as foreign institutionsdemonstrated a strong interest in this field. We plan to organize follow-upworkshops in the future emphasizing specific research topics.
H. Gordon BerryYoshiro AzumaNoura Ber'rah Mansour
Alan Schriesheim COMMENTS:APS WORKSHOP ON ATOMIC PHYSICS
March 29, 1990
Ladies and Gentlemen, it is a pleasure to welcome you to Argonne NationalLaboratory and to this workshop on the ways that synchrotron radiationgenerally, and the Advanced Photon Source (APS) specifically, carl advanceatomic physics.
We are pleased to see you here for a variety of reasons. For one thing, wewant you to know all that we are doing to get the APS ready for your use. Foranother, we welcome the chance to learn from the leading researchers in the fieldwhat you are doing in this area of science.
Most of all, we want to be sure that all of us are prepared to utilize fully theAPS as a vital new tool. The combination of high intensity and high-energy x-raysprovides unique opportunities in atomic physics, particularly in studying theprocesses that follow deep-inner-shell electron dislocation.
First, let me tell you about our progress. Many of the current developmentsthat will affect the future of the APS are in a peculiar corner of science known as"political" science.
We are receiving $51,5 million for APS construction and supportingoperations this year. We expect to break ground about a month from now.
The Department of Energy's spending plan, which is reflected in President: Bush's 1991 budget proposal to Congress, supports construction which would
_llow us to start research in the fall of 1995. Some members of Congress feel thatwe can optimize the nation's financial investment by shortening that constructionschedule.
This would require $120 million in APS funding for 1991 instead of the $75= million in President Bush's proposed budget to Congress. I've discussed this
accelerated schedule with Secretary of Energy James Watkins. He has indicatedto me privately and to Congressional hearings that he would welcomeincremental funding for such a purpose.
We are ready to accelerate this project. We have been hiring staff as fast asfimds are released to us for that purpose. Currently there are 165 Argonne peoplein the APS orgamzation.
The cultural, archeological, geological, and soil work on the constructionsite is either on schedule or completed. The study which found no significantenvironmental impact has been approved by the state Department of Energy andis moving forward toward approval by the federal DOE.=
',qNI_ ni
Both the architect-engineering contract and the construction managementcontract have been signed with leading national firms.
The first quadrupole magnet to focus the positron beam has been shipped tc_Fermilab for testing. The prototype undulator which will wiggle the positronbeam in order to generate brilliant x-rays has been designed by APS for testing atBrookhaven National Laboratory.
Testing continues on the aluminum vacuum chamber prototype. And weare advancing development of a unique design to run liquid gallium throughchannels in the silicon crystals that act as polarizing mirrors for the x-ray bearn,both to cool one side of the crystal and to heat the opposite side to offset distortion.
In collaboration with researchers at the University of Michigan _ndAT&T's Bell Laboratory, we have developed a charge-coupled device to makeultra-fast x-ray diffraction images of materials under stress.
We are also preparing our staff to make this the most user friendly facilityever built in the United States. And I don't mean just the APS Staff.
With 200 research programs, Argonne probably can claim the mostdiversified mix of disciplines and expertise of any national laboratory. We believethat diversity represents an advantage for both this Laboratory and for the users of'APS.
It offers you a smorgasbord ofcollaboratioll and assistance ranging fromtheorists and experimentalists through advanced computer specialists,accelerator engineers, and technicians.
It is our goal to have each user of APS spend the maximum amount of thetime at Argonne on the experiment. We expect to apply what _e have learned inthe operation of our other accelerators -- like the Intense Pulsed Neutron Sourceand ATLAS -- to save the user time on setting up, operation of the facility,collection of data, and bureaucracy.
That is why it is important for us to have you here for thi_ workshop and tolearn what you foresee as your needs when we start generating the most brilliantx-rays in the world. Thank you again for coming to this conference and for yourcontinuing interest in the Advanced Photon Source.
PRESENTED PAPERS
'_' _11' _M',,lrjl,'_ll"'lNIl_llH_l"r_,, "rl..... _ '" Ii ......
STATUS REPORT ON THE ADVANCED PHOTON SOURCE, SPRING 1990
by
David E. Moncton
Associate Laboratory Director, Advanced Photon SourceArgonne National Laboratory
INTRODUCTION
The Advanced Photon Source (APS) at Argonne National Laboratory has beendesigned as a national user facility for synchrotron-radiation lesearchers fromindustry, universities, and national laboratories. In fact, the APS user communityhas been an important source of guidance and expertise throughout the p_'oject'splanning cycle.
By providing x-ray beams more brilliant than those currently available, the APSpromises to play a substantial role in anydiscipline where knowledge of thestructure of matter is important, from basic research in materials and chemistry tocondensed-matter physics, biology, and medical applications. The science now inprogress at existing synchrotron-radiation facilities, and the science being proposedfor the APS, underlie virtually all modern technologies.
In February of 1986, a conceptual design report (CDR) was issued detailing plansfor a next-generation synchrotron-radiation machine, the 6-GEV Synchrotron X-raySource. In April of 1987, a second CDR formalized the design of the 7-GEVAdvanced Photon Source. That design has been refined and carried forward to itscurrent level of construction readiness. On the eve of ground-breaking ceremonies,a review of APS status is appropriate.
APS FACILITY OVERVIEW
The APS facility is to be constructed in the southwest corner of the Argonne siteon a 79-acre parcel of land with very good geological characteristics.
The experimental hall will be 390 meters in diameter, with the storage ringnearest the inner wall of the large hall. The linac, positron accumulator ring, andbooster are to be located in the infield. Lab/office modules for users will be located
around the perimeter of the ring. Staff and long-term visitors will occupy an officebuilding situated olltside the ring. The APS will provide research opportunities forseveral thousand scientists in total, with 300 to 400 taking data at any one time.
The 58-m-long, 60-Hz APS linac will initially accelerate electrons to 200 MeV.One-third of the way down the linac, the electrons will impact on a tungstenpositron-conversion target. Positrons will be captured and accelerated to 450 MeVover the remaining two-thirds of the linac and then injected into a smallaccumulator ring, approximately 31 meters in circumference, where successive 450-MeV pulses from the linac will be stacked. The accumulator ring serves twofunctions: to damp the positron emittance, thereby making the beam more compact,and to accumulate 24 pulses from the linac while the booster is ramping-up the
previous set of pulses. After injection into the 368-m-circumference booster,positrons will be ramped-up from 450 MeV to 7 GeV in one-quarter of a second.Because it cycles back down to 450 MeV in order to pick up the next pulse, thebooster performs two cycles per second, making it a 2-Hz machine.
The storage ring, 1104 meters in circumference, is designed for a nominal energyof 7 GeV. All calculations of undulator spectra indicate an optimal energy rangebetween 7 and 7.5 GeV. At higher energies, the performance of undulators in theprincipal x-ray range, where APS will operate, begins to ,--leteriorate, making 8, 9, o1"10 GeV problematic in terms of usefulness. Under normal operating conditions,about 30 of the 1296 available rf buckets will be filled with positron bunches, each
carrying on the order of 5 milliamps. Anticipated filling time is one minute.The APS storage ring will have 40 sectors that each include a straight section.
Each sector will contain one insertion-device (ID) beamline and two bending
magnets. One of the two bending magnets in each sectorwill be available to extractradiation; thus, a sector from the user's point of view is an insertion device and itscompanion bending-magnet beamline. Allowing for rf cavities and injectionapparatus, there will be 34 sectors available to user groups.
APS undulators will produce x-ray beams withspectral brilliance in the rangebetween ! 018 and 1019 photons/s/0.1%BW/mrad2/mm 2. That brilliance represents anincrease of 3 or 4 orders of magnitude over what is now available from, for instance,bending magnets at the National Synchrotron Light Source. There are other deviceswhich perform in the intermediate range, but nothing extant in the U.S., or in factthe world, is capable, certainly on a dedicated basis, of producing brilliance at thelevel to be achieved by the APS.
Space for users at existing synchrotron-radiation facilities has historically been inshort supply. The APS design calls for one user module, containing two labs andcomplementary offices, for each sector of the machine, providing a significantimprovement in the quality of life for the research community around the ring.
RESEARCH AND DEVELOPMENT HIGHHGHTS
Insertion devices
A collaboration between the APS Experimental Facilities Division (EFD) and re-searchers at Cornell University resulted in the design of a new insertion device, theAPS/CHESS undulator. APS staff then worked with Spectra Technology ofBellevue, Washington, to construct the lD, and in 1988 the prototype APS/CHESSundulator was installed at the Cornell Electron Storage Ring, where it performedextremely well.
A prototype ultraviolet undulator has now been constructed and it will soon betested in the vacuum ultraviolet ring at Brookhaven National Laboratory. Currentlyunder consideration is a device to produce circularly polarized radiation, an advancecertain to be of interest in the atomic physics community.
OpticsThe problem of thermal loading on beamline optical components is also the
subject of an EFD study. When an intense x-ray beam strikes a monochromating
crystal or a mirrored surface, that surface is heated, causing a distortion, or localthermal bump. These high power densities, which will occur at unprecedentedlevels at the APS, would be disastrous to a beam's optical quality. A multi-stepprocedure developed by APS staff will model the effect of localized high heat loadson optics. Using the Cornell machine and beams from the prototype APS/CHESSundulator, _he resu!ts of th.ese calculations have been intercompared withperformance to determine the reliability of ,'he finite--element..analysis approach andto optimize schemes for optics cooling adequate to the needs of APS.
While the state of the art in optics cooling has been to run water through_-ha'anels close to the surface of a crystal, Argonne scientists have pioneered the useof l_quid metals, particularly gallium, which is much more effective as a coolant. Atthe current stage of development, APS-designed optics can withstand the powerdens_ities associated with beams carrying brilliance levels in the 1018 range. Further
j optindzation of that geometry will be carried out to accommodate the even greaterpower densities that will c_me with the I019 brilliance level produced by the fullyoperational APS facility.
Acce..eJ'ator physicsAnti_:ipating the behavior of particles in a storage ring is among the most
daunting of accelerator-physics issues. The APS Accelerator Systems Division (ASD)is performing a series of experiments using the Aladdin storage ring at theSynchrotron Radiation Center _n Wisconsin. These experiments serve as a check oncomputer programs that must predict the behavior of particle dynamics in the APSstorage ring, as measured in respor_.se to perturbations. Under experimentalconditions, APS simulations have proven to be very accurate. The measurementsalso resulted in specific determinations about the operational parameters of themagnets in th: Aladdin ring. conditions which were not known at that level ofdetail at that time, making this undertaking useful for scientists at Aladdin as wellas at AI_...
Vacuum chambers
There will be 240 sections of vacuum charr.lber, each approximately 15 feet long,in the storage ring alone. Three actual, though non-production, storage ring
i_ vacuum-chamber segments, complete with all welds, hardware, and ports, havebeen constructed by the Accelerator System_ Division. Fabrication of these chambersrequires ir_tr_cate we.l.ding to allow connection, of all segments in the ring. An
' innovative weld,.'ng technique has resulted from the R&D effort carried out withFerranti Sciaky, Inc., of Chicago.
• Configuring vacuum chambers to match ring curvature has not been a trivial• matter. It was realized that if the chambers could not be bent, they would require
machining, a _uch more expensive alternative. A method for bending thechambers, the subject of an R&D initiative begun two years ago togetber with PacificPipp. of Oakland, California, ha oeen successfully demonstrated, putting to rest a keytechnical and budget issue.
MagnetsAs there will be a total of 1503 magnets of various types in the APS accelerator
complex, R&D in this area has also been a focal point for the Accelerator SystemsDivision. The first of 400 APS storage-ring quadrupole (SRQ) magnets has beenassembled from components fabricated to APS specifications. The SRQ, though astraightforward electromagnet, is very demanding in terms of magnetic-fieldquality: Storage-ring quadrupoles for the APS require field gradients accurate to 1part in 104, maintainable even after disassembly and reassembly for repair. Criticalparameters must also be achieved economically over the entire SRQ fabricationcycle, as they must for all APS magnets.
The prototype 0.8-m-long SRQ was transported to Fermi National AcceleratorLaboratory for magnetic measurements, which proved to be within the requiredmargin of error. Slight design modifications are now under way prior to assemblyand testing of a second SRQ. In order to expedite the measurement process, an APSmagnet-measurement facility is scheduled to be on line at Argonne in the summerof 1990.
FUNDING
The 7-GEV Advanced Photon Source Conceptual Design Report proposed aconstruction budget of $380 million (expressed in FY1989 dollars, as are all amountshere), with $77 million of that sum for contingency and a detailed estimate totaling$303 million for technical components including the injector, the storage ring,insertion devices, and beamlines. Since then, that estimate has held up as the APSprogressed from conceptual design to a completion level of 30 percent. Though costshave risen by $30 million, the contingency has dropped to $49 mill':'a as moreknowledge about the design has been gained, the motivation for setting a largecontingency at the outset. Escalation in the cost of conventional construction,currently estimated at $I47 million versus the CDR estimate of $115 million, hadbeen the cause of some concern. However, in the last few months, value-
engineering studies have identified approximately $16 million in cost containmentsfor conventional-facilities construction. Over all, the project co'-' estimate has risenby only one percent.
The schedule now on file with the Department of Energy, the Office ofManagement and Budget, and the Congress, calls for $40 million in FY1990 tounderwrite early construction activities, as well to purchase some technicalcomponents. In FY1991, APS is scheduled to receive $75 million, with fundingescalating through _Y1993 and then tailing off over the next t,._o years for a total of$456 million at completion in 1995.
Project management has developed an accelerated funding profile, calling formore initial dollars but no increase to the total of $456 million, which would allow
completion of the APS a year earlier. That possibility has been communicated, andthere has been some enthusiasm for it within the Department and Congress.
These next few months will be critical to the progress of the Advanced PhotonSource. If the case for an accelerated funding schedule is made, perhaps the AIX3 will
10
have some chance of competing with next-generation facilities being constructed inEurope and Japan.
LEITERS OF INTENT
APS user programs are approaching an important date. May 1, 1990, has been setas the deadline for submission of' experiment proposals in the form of Letters ofIntent from prospective users, both Independent Investigators and CollaborativeAccess Teams. Those Letters of Intent that are approved will move on to the formalproposal stage. Finally, there will be a third stage, where a memorandum ofunderstanding is signed cementing relationships between users and the Laboratory.
Ali those associated with the APS can view May 1 as that point in time when thevariety and scope of research interests will come into clearer focus, and the APS'strue potential will begin to take shape concurrent with its physical manifestation.
11
Workshop on Atomic Physics at the Advanced Photon Source
Argonne National Laboratory, 29-30 March 1990
OPPORTUNITITES FOR ATOMIC PHYSICS WITH HARD SYNCHROTRON RADIATION
Bernd Crasemann
Department of Physics, University of OregonEugene, Oregon 97403
Introduction: Construction of third-generation synchrotron-radiation facilities places atomic and molecular scientists at
threshold of extraordinary opportunitites.
Complementarity of APS and ALS. Here emphasize applications
of hard x rays.
History of x rays recent. Importance in development of
"modern" physics--crucial experiments on wave-particle dualism,structure of matter.., yet limited. Continuous source of EM
radiation from transverse acceleration of charged particles seen
in supernova remnant in Crab. Properties of SR from synchrotrons
and storage rings predicted IB98 by Li_nard, cf. also Schott 19i5,
calculated by Schwinger 1946, '49 and Sokolov and Ternov 1968.First observed in 1947, initially considered nuisance. Only in
last 3 decades the realization has grown that this source of
These perspectives were surveyed by a Panel at a Do___E_Workshopheld in Berkeley last November; its report and those of other
panels dealing with additional frontier research areas in AM0sciences are to be discussed at a "town meeting" on the last
evening of the DAMOP annual meeting in Monterey 21-23 May. Ap-
propriate to take the Panel Report as starting point here, expand
upon unique potential of hard x rays in the production of whichthe APS will excel.
Subjective view of "Global Frontiers" (note qualifiers). Strongpotential of APS likely to lie in part in exploration of relati-
vistic and EO_effects which become prominent in inner shells and
at high Z---cf. later.
Techniques and topics---provide selected illustrations:
Total photon interaction cross sections [Absorption spectromet-ry] ....Technological applications from medical radiology to space
travel---discrepancies near edges; mar_y-body effects; ill-unders-
tood phenomena. Clear resolution at ix_ner thresholds---cf. Xe LS---need to extend.
12
Scatterinq---Molecules and atoms to nuclei; cf. George -9Brown's lecture---nuclear Bragg scattering, resonance width 10
eV! Fe-57 in YIG, sees enhancement o_f_fcoherent decay: broadening
and shift; qaantum optics analog.
Fluorescence---cf. Lindle et al.'s discovery of polarizationdependence of Cl K-beta from CH3CI (methylchlorlde) on excitationenergy in the C1K region---deduce molecular orbital symmetries
(Peter Langhoff): a consequence of the alignment of the molecule
produced by the excitation process. Foresee applicability to more
complicated molecules, adsorbate and condensed phases!
Photo- and Auger-electron spectrometries---workhorses of atomic-
structure and dynamics investigations, anticipate more angle- and
spin-resolved and coincidence measurements made possible by high-er brightness---cf. Manfred Krause's lecture.
Especially fruitful now: e-e correlation studies by thres-
hold ("zero-energy") tlme-o_-flight electron spectrometry.
Further example: Tulkki-Krause Xe 5s threshold satellite:
cross section at t_reshold dominated by Interaction between !5s]single hole and 5p 5d double-hole ionization channels---new 'in___x_-
ternal electron scatterln_ satellite" with peculiar dynamical
properties dominates at threshold!
Ion spectrometry---Note paucity of data. Frontier. Cf.
Wuilleumier lecture. Church reviewed andrecently brightness
storage techniques. Plans for tr___s incl. EBITs in SR beams.
For remainder of talk, turn in slightly more detali to a couple
of challenging questions regarding atomic inner-shell phenomena ....
A sDecial re i_in which APS will lend access to unprecedentedexploration... Illustrate.
Atoms held together by the Coulomb force, hence it is importantto look at the lowest-order relativistic corrections to the
Coulomb energy, viz., current-current interaction [exchange of a
single transverse photon] and retardation effects.
Breit operator accounts for small contribution to total energy---
but can get significant in special cases, e_g. hyperfine split-
tings and two-hole-state energies...
Energy matrix element between antlsymmetrized j-j-coupled 2-hol_states.
Test p_ediction_ by locking at hypersatqllites, Note K-alpha-one-h [is ]-[_s2p]-Pllforb!dden in LS coupling, emission depends onmixinq of _PI and P1 in [2s2p] final state---reduced by Breit:
25% effect at Z=lS---but mixing is increased for higher Z!
Note from classical ratio of two indiscrepancy K-alpha-one/K-
alpha-two hypersatellite intensity ratio vs. Z! What fun to check!
13
Similar large contributions of Breit to e_zr,e_Er_Ly_shifts---clearopportunity for sensitive tests of Mann-Jchnson operator.
Another class of atomic inner-shell processes that deserves being
singled out because important investigations w_Jl become possible
with the APS relates to virtual (i) Interaction of_henomena :hole states with the continuum, and (2) resonant Raman transi-
(' tJ ons.
Interaction,with-radiationless-continua effect on level energies.
Second type of interesting virtual transitions, barely explored
Tomas Baer, University of North CarolinaBernd Crasemann, University of OregonJ.L. Dehmer, Rrgonne National LaboratoryH.P. Kelly, University of VirginiaH.O. Kraose, Oak Ridge National Laborator9D.W. Lindle, Natl. Inst. of Standards & Tech
17
Gl_ib_ _rontiersin Scienceinolude
* STRUCTUREof atoms and moleoules andDYHRMICSof processes --
• _ectron spectroscopy- Cross sections, angular and spin distributions- Multielectron effects- Resonant photoemission• i
- Post-collision interaction
• Auger-electron spectrometry- Auger ylelds- Energy levels of multiply charged ions- Satellites and many-elecWczon effects- Time-resolved studies- Threshold resonances- Cascade effects- Post-collision interaction- Angular distributions- Spln-resolved spectrometry- Coincidence studies
Q Ion spectroscopy" - Molecular fragmentation
- Multiple ionization- ' Ion coincidence studies- Studies of trapped ions
•- Two-color experiments
19
2O
ii
• ill
V()Z.UMI:63, NtJMJ31!_t15 PIIYSICAL REVIEW LETTERS 9 OCTOBER 1989
Resonance Energy Shifts duringNuclear Bragg Diffraction of X Rays
J. Arthur, G. S. Brown, D. E. Brown, and S. L. Ruby
Sta,_ford Synchrotron Radiation Laboratory, P.O. Box 4349, Bin 69, Stanford, California 94309(Received 12 June 1989)
We have observed dramatic changes in the time distribution of synchrotron x rays resonantly scatteredfrom STFe nuclei in a crystal of yttrium iron garnet, which depend on the deviation angle of the incidentradiation from the Bragg angle. These changes are caused by small shifts i_ithe effective energies of thehyperfine-split nuclear resonances, an effect of dynamical diffraction for the coherently excited nuclei inthe crystal. The very high brightness of the synchrotron x-ray source allows this effect to be observed ina 15-min measurement.
FIG. I. "lime distribution of resonantly scattered x ray:,-
from YIG (002) in symmetric Bragg geometry, with tl_e indi-cated deviation angles from the Bragg angle (corrected for re-fraction due to the electron density). Each solid curve gives
° the intensity of the Fourier transform of the dynamical theorycalculation for the multilevel energy-dependent reflectivity am-
plitude.
PHYS. REV. LETT.60, 1010 (1988)
Polarization of Molecular X-Ray Fluorescence
D. W. Lindle, P. L Cowan, R. E. LaVilla, T. Jach, and R. D. DeslattesNational Bureau of Standards, Gaithersburg, Maryland 20899
q
B. KarlinNational Synchrotron Light Source, Brookhaven National Laboratory, Lipton, New York 11973
and
J. A. Sheehy, T. J. Gil, and P. W. Langhofl"Department of Chemistry, Indiana University, Bloomington, Indiana 47405
(Received 7 December 1987) "i'.__,,,_2r:,¢
Polarization of CI K,B x-ray fluorescence following selective excitation of gaseous CH._CI with syn-chrotron radiation is reported. The degree of polariza!ion .of the fluorescence depends sensitively on thechosen incident excitation energy in the CI K-edge region. Theoretical considerations indicate that the
fluorescence-polarization measurements can provide directly absorption and emission anisotropies,molecular-orbital symmetries, and relative fluorescence transition strengths.
FIG. 2. CI K3 fluorescence spectra from CH3CI followingCI Is--* 8at excitation with 2823.4-eV photon energy, centeredon feature D in the absorption spectrum of Fig. I. The labelsparallel and perpendicular refer to orthogonal orientations ofthe measured fluorescence polarization relative to the incidentE vector. The two spectra have been scaled so that the areas of
peak C are identical. The peak at 2823.4 eV is due to elasticscattering of the incident radiation.
22
PHYS.REV. LETT.62, 2817 (1989)
Muitiple Excitation at Xezon 5s Photoionization Threshold
2 "l'ulkki
Research Institute for Theoretical Physics, Unit'ersity of He!sinki, 00170 Helsinki, Finlandand Laboratory of Physics, flelsinki Umrersity of Technology, (,) 02150 Espoo, Finland
(Received ,28March 1989)
The effect of multiple-electron excitation on the threshold behavior of Xe 5s photoionization is studied
using the multichannel multiconfisuration Dirac-Fock method with full account of relaxation. The in-clusion of the ionization channels related to 5p"5d .]ion " 7 excited states is found to change the single-
excitation results drastically. Our cross section and asymmetry parameter/3 are in very good agreementwith experiment. Calculation of the related satellite cross sections predicts a new type of satellite thatexists only in the near-threshold region and has a peculiar ang,ular dependence.
PAtsn,o,bo,: 32.SO.Fb [5s] "_%
5p45d _- (a)
, ..,_ 2015 ______..._.._=_7 -- _ 1.0 v
0.5 _- '_ "'" .....t.. ; V ,,.,., - "
0.0 L. v ..-"" r.:.. _ 0.5 Vv . -"
. ,,,'
-1.O _ ""' , ', ' _ , I , _ • '
(b):E
o • 1.3._ "... - _,0 0.I0 11 .._
co 0.90.05 . --
-. 0 0.7 rn
0.00 ........... 0.5 I,,")
30.0 35.0 400 45.0 50.0 55.0
Photon energy (eV)
5p45d photoelectron satellites
_ Experiment: Fahlman Krause Carlson and Svensson_ I ! I !
° Phys. Rev.A 3...Q,812 (1984)_
- 23
..... i ii
i, I I I I I i i ..... III ii I IIii 1 • --.-.jI
From Church et al., Physical ReviewA 36, 2487 (1987).
Signals from argon ion charge states, obtained using axial detection of the ions ina Penning ion trap. The ions were generated by a vacancy cascade followingsynchrotron radiation photoionization of argon.
24
'_11' II
ATOMIC INNER SHELLS_
LARGE ENERGIES e.g. E(ls) _----100 keV, Z _--87
---->ISTRONG REL.+ GED EFFECTS l*
m/mo =_1o05at Z/n = 43, also Ar -->AIE(ls)I ---5% at Z ---61
STRONG_TRANSITIONS e.g. r'(M1) _-_-20 eV, Z --90
MOSTLY RADIATIONLESS. e.g. o)(M1).-=-10-3, Z =70
MANY..CHA.NNEL_ e.g. 2784 matrixelements to [2P3/2]at high Z
VERY,,£HORT"_'s (< _'BOHR)
---> PERTURBATION APPROACH PUSHED TO LIMIT
TWO-STEP SEPARATION OFEXCITATION/DEEXCITATIONBREAKS DOWN *VIRTUAL PROCESSESPLAYIMPORTANT ROLE
* ILLUSTRATE -
25
m
_f__lT' Ir,IT-IF-I_ACT'IO r,_-
J'='lf_ST _OYNP, m_C-- C_I_I_.CTI_P4 "TO THE.
E LEC Tf_.OST'_TI¢ C_uI...0 lMr_ I I_'i-_-i_A CTIO N
[ I_ TH_ {'_.(=.-I,.. AT'i q_ $ T, C.. H At'_ tL.TON, I Ab"
4. Photoionization cross section of K+ from Ref. 7. The points
are experimental, the upper curves are calculated relativisticramdom phase approximation results with and without intershell
coupling, and the lower curve is the calculated central-field• result.
47
From Physica Scripta 41,458 (1990)
i0l ' ls2 1S" lsnp 1po1 . 71_514 3 £1I
CV ,o.5 II4I
K
o,8_ CJvii
0,4L I
I
,Kti
1._L
CIII
IAI,! '0,01 'lJ t _i,u _.,
25,0 30,0 35.0 40.0 ,45,0 ,/,
5. Experimental absorption coefficient of ions of carbon in the
region of the Is threshold from Ref. 8. The dashed line in
the C V spectrum is te theoretical result of Ref. i0.
48
From Physical Review A .,_.Z,1047 (1988)
4f
5f,"!/
/J
, Calculated photoionization cross sections for excited nfstates in Cs from Ref. 9.
From Physical Review A ._3.Z,1047 (1988) ., 5f
//
//
/
" Ba/// 1 +'8f
I// I i101 19f
tl '
1°° Ii sf
,,_ 10"1 !L L __ , , , ,
I ! /1 6f /,"v 10-2 _ i ' ' '
b s"i / I "/
't 7f /
10-3 - ' - ._v'II
10-4:_ I, .....i
,.
10_5{, 9fi j ,,
0 1 2 3 4 5
6, R
7. Calculated photionization cross sections for excited nf statesin Ba+ from Ref. 9.
5O
FromPhysicalReviewA .,3!,1047(1988)
101 I I 1 I I
loo 6f
. 10-3
o 1
10-4 , l t0 1 2 3 4 5
G / R8. Calculated photoionization cross sections for excited 6f
states in the Cs isoelectronic series from Ref. 9._
= 51
From Physical Review A 18, 2124 (1978)
9. Calculated 2s photoionization cross sections (per election)for ions in the Fe isonuclear series from Ref. ii. Thevertical lines are the thresholds for the given stage ofionization.
52
From Physical Review A 18, 2124 (1978)
0.05
5 10 15 20 25
hIJ(RYDBERGS)
i0. Calculated 3p photoionization cross sections (per election)for ions in the Fe isonuclear series from Ref. ii. The
vertical lines are the thresholds for the given stage of
ionization.
53
54
Adapted from Aust. J. Phys..3.._,799 (1986)
1.0I 1 L -0 1 2 3 4 5 6
hU(RYDBERGS)
14. Calculated branching ratio of 3p:ip final states in 2s
photoionization of B from Ref. 14. The curves labelled L and
V represent "length" and "velocity" results, while K includes
only the shift of thresholds. Note that in the absence of
dynamical effects, this ratio should be three.
57
DETECTORS
ee
/////,,," ////II
I III I I
+hv
A A A _ A A _,* _
15. Schematic representation of photoelectron-auger electron
energy and argular correlation (coincidence) experiment.
58
Advanced
: Light
Source
THE ADVANCED LIGHT SOURCE:A NEW 1.5 GEV SYNCHROTRON
RADIATION FACILITY AT THELAWRENCE BERKELEY
LABORATORY
Fred Schlachter
University of CaliforniaLawrence BerkeleyLaboratoryBerkeley, CaliforniaUSA
59
r_._A_dvance d
THE ADVANCED LIGHT SOURCE
The Advanced Light Source (ALS), presently under construction at theLawrence Berkeley Laboratory, will be the world's brightest synchrotron-radiation source of ultraviolet and soft x-ray photons when it opens its doors tousers in April 1993. The ALS is a third-generation source that is based on alow-emittance electren storage ring, optimized for operation at 1.5 GeV, withlong straight sections tbr insertion devices. Its naturally short pulses are idealfbr time-resolved measurements. Undulators will produce high-brightnessbeams from below 10 eV to above 2 keV; wigglers will produce high fluxes ofharder x-rays to energies above 10 keV.
The ALS will support an extensive research program in a broad spectrumof scientific and technological areas. The high brightness will open new areasof research in the material.s sciences, such as spatially resolved spectroscopy(spectromicroscopy). Biological applications will include x-ray microscopywith element-specific sensitivity in the water window of the spectrum wherewater is much more transparent than protein. The ALS will be an excellentresearch tool for a_omic physics and chemistry because the high flux willallow measurements to be made with tenuous gas-phase targets. Undulatorradiation can excite the K shell of elements up to silicon and the L shell of'elements up to krypton, and wiggler radiation can excite the L shell of nearlyevery element.
The ALS will operate as a national user facility; interested scientists areencouraged to contact the ALS Scientific Program Coordinator to exploretheir scientific and technological research interests.
Fred SchlachterScientific Program CoordinatorAdvanced Light SourceMS 46-161Lawrence Berkeley LaboratoryBerkeley, CA 94720
60
THE ADVANCEDLIGHT SOURCE:SOME ESSENTIALS
Designed for the VUV and softx-ray region; optimized for 1.5-GEVelectron beam energy
-_ Based on an electron storage ringwith 12 straight sections, 197 meters incircumference
_ Includes provisions for about 60beamlines, including 11from insertiondevices
.Stored beam to have extraordinarilylow emittance,short pulses
Construction now under way at theLawrence Berkeley Laboratory; to beoperational in April 1993
61
The ALS and APS complement eachother
Wavelength ot_) o°104 103 102 1 1,,
_: _I ' ' I "' .....' 'I ' ' I ' ' I ' ' .£13
1020-_9, - ALS Undulators,--- APS -
0 - U3.9 Undulators
. -[;:::1018" _
E - u8_,/-- _
e4 "" ' N "
. _ _ 'E_ 016 -k_. I -- "-
E - w13.6-
0O
_1014 -C0 -
0c-
13--1N 12- , i I , , , I , ,, _ ,/ _.J¢
10° 101 102 103 104 105
Photon Energy (eV)
62
A Brief History ofSynchrotron Radiation
The instantaneous total power radiated by a nonrelativistic electron was first expressed by Larmor
in 1897, using .classical electrodynamics:
p_ 2 e 2 I_.,lluvl23 e3 Idt, I
-h-Synchrotron radiation was first observed at the GEResearch Laboratory in Schenectady, NY in April1947, on a 70 MeV electron synchrotron built partlyto test McMillan's synchrotron principle.
_r A 7-pole wiggler was used as a synchrotronradiation source at SPEAR in 1979.
_r Halbach's idea of using strong permanent magnetsmade from rare-earth elements and cobalt instead
of electromagnets made undulators practical VUVand x-ray sources.
_A permanent magnet undulator developed jointly byLBL and SSRL was installed at SPEAR in 1980. Its
output was four orders of magnitude higher thanthat from a SPEAR bend magnet.
63
MODERN SR RESEARCHFACILITIES
"First Generation" facilities were initially parasiticoperations at existing high-energy physics facilities:
"Second Generation" facilities are dedicated buthave limited magnetic insertion device capability:NSLSat BNL LongIsland,NYAladdinatWisconsin Madison,WlB_Y WestBerlinPhotonFactory Tskuba,JapanSuperACO Orsay,France
"Third Generation" storage rings are specificallyoptimized (long straight sections and low beamemittance) for magnetic insertion devices:ALS at LBL Berkeley, CaliforniaTSL (SRRC) Hsinchu,TaiwanSiberiaII (Kurchatov) Moscow,USSRBESSYII West BerlinSincotroneTrieste Trieste, ItalyPLS Pohang,Korea
JAPANOkasaki UVSOR (IMS) 0.6 DedicatedKansai area 8 GeV Ring 6.0 Design/DedicatedTokyo SOR (ISSP) 0.4 DedicatedTsukuba TER? S (ETL) 0.6 DedicatedTsukuba Photon Factory (KEK) 2.5 Dedicated
Accumulator Ring (KEK) 6.0-8.0 Partly DedicatedTristan Main Ring (KEK) 25-30 Planned Use
SWEDENLund Max (LTH) 0.55 Dedicated
USAArgonne, IL APS (ANL) 7.0 Design/DedicatedBerkeley, CA ALS (LBL) 1.5 Dedicated*Gaithersberg, MD SURF II (NBS) 0.28 DedicatedIthaca, NY CESR (CHESS) 5.5-8.0 Partly DedicatedStanford, CA SPEAR (SSRL) 3.0-3.5 Partly Dedicated
PEP (SSRL_ 5.0-15.0 Partly DedicatedStoughton, WI Aladdin (SRC) 0.8- ! ,0 DedicatedUpton, NY NSLS I (BNL) 0.75 Dedicated
]}RIGHTNESS OF X RAYS has izlcreased l=ryma_ orders of mag_tude since the adv_tof s3_cb.rotro_d._Ucm sources. Undulators in storage rings are the briE31te_ source.
68I
Technological advances have madepossible third-generation synchrotron-radiation sources
1 ) ALS construction site with model of finishedfacility, which will be ready for users in the springof 1993.
2) LBL site is on the hillside above the University ofCalifornia at Berkeley campus. Dome atop the old184-Inch Cyclotron building will crown the newALS building, as weil.
3) The ALS site stands out in this aerial view of LBL.
4) The 184-Inch Cyclotron, built by E.O. Lawrenceduring WWII, was the first major facility on thecurrent LBL site.
5) The ALS building will consist of an annularaddition surrounding the renovated cyclotronbuilding. Here the contractor is putting in thefoundation for the addition.
6) Structural steel for the addition was in place bythe end of 1989.
7) Diagram shows the main components of the ALSfacility.
71
1 2
73
74
?6
Pl
77
VI'Y"_AJdvanced
_rLightI$ource
j'"" _ " TheAdvanc_ LightSource
/ ' and bend ng magnet "/E xPe',me n'al areas,L_'_'k_C-i' _.Z"_"_== ...... _a' beamne s
"--.- _L'_ ., I. ----__-___.-...,__X_"_-___-__-_----___-_ __..__---_.____ -,,_.
synchrotron radiation
'
i Monochromator |
Ex,_,,,__'- "'"_i""%.Y
78
CHARACTERISTICS OF THE STORAGE RING
ALS
• Store 1012 relativistic electrons for six hours
while controlling their positions to --50 microns
(in six hours they travel four billion miles)
• This _'equires
- Precisely'engineered magnetic lenses, dipoles, and higher
order correction magnets
- A sophisticated understanding of the dynamics of high
charge density electron bunches in non-linear magneticfields
- Precise beam sensors and feedback systems
- A vacuum channel for the beam of 10 -9 Torr, even with the
x-rays present to desorb gas from walls. Otherwise,
scattering on gas disrupts beam.
- A powerful radiofrequency accelerating system (--,300kW of
. power @ 500 MHz) to resupply the energy emitted as x-rays
- A very sophisticated control system to monitor and controlall of this
• beam size and position must be carefullycontrolled
8O
--
ALS electron bunch structure
Gaussian pulse
• .-_,_\ (rms)
20% of C = 196.8 m - - \I FWHM>--35 pS
buckets I= 400 mA k"_ / iunfilled (1.6 mA per bunch)for _ion 328 buckets available, ]'FWHM = 2.35 _ timeclearing nominally operate
with 250 filled
|'FWHM "_ 35 ps (nominal)500 MHz RF
"V""V" l --II...... 2 ns ...... I
O O,,4 ..
35 ps 35 ps
" Schematic illustration of the electron bunch structure in the ALS
. storage ring during multibunch operation. As shown at the upper right, eachbunch has a full width at half maximum of about 35 ps. The spacing between.
bunches, dictated by the rf frequency, is 2 ns. (The electron pulse length is thus1.75% of the bunch-to-bunch interval. If rendered to scale, the illustration at
the left would show 250 narrow spikes, distributed around 80% of the ring's cir-
cumference.)
m=g
i
81
..
BEAM UNE II
C RAD_O-FREQUF._CAvn'Y
UNOULATOR :,
\
A
COIL WINDINGS
STORAGE RING dedicated to the production oi' synchrotron radiation is structuredaround a ring-shaped vacuum chamber through which a beam of electrons circulates.An oscillating electromagnetic field established in a radio-frequency cavity providesenergy to maintain the particles at relativistic speeds (nearly as fast as light) after theyare injected into the ring from an external accelerator (not shown). Quadrupole andsextupole Ibcusing magnets confine the electrons in a tight beam by means of fields setup by fbur and six poles, respectively, arranged radially around the vacuum chamber.Bending magnets three the electron beam to curve, causing the particles to emitsynchrotron radiation (black areas). The ring may also include other magnetic devicesknown as wigglers and undulators that substantially increase the "brightness" of theradiation_a measure of' its concentration. Pipes called beamlines channel theradiation ii'ore the various magnetic device.,_ to experimental stations.
- 82
_
ALS lay.out: i_j_to_,booste_,storage ring............1.5 GeV
\\
",, \
/ ",, _
/ _"%
! i \. 'i/ I_ /
\ '
,, 1.5 - GeV Booster " i
"_ Synchrot- "'.-,,,,Storage ring
012 4 6 8 10
Scale in meters
Main Parameters of ALS Storage RingBeam energy [GEV]
Nomina_ < 1.5;//
Minitt_).'_., ,, 1,0 .
Max,_'_,_m/ 1.9,, (
Circumference fm] 196.8
Beam current [mA] :.,
Multibunch ' 400Single bunch 7.6
Beam emittance, rms [nra.rad]
Horizontal 10Vertical 1
Relative rms momentum spread
Multibunch 8.0 X 10-4Single bunch 13.0 X 10-4
Nominal bunch duration, FWHM [ps] 30-50
Radiation lossper rum [keV] 92
Length available for insertion devices fm] 5
ALS triple-bend achromat lattice
/" B SD QFA SF B,! SF QFA SD B QD QF " "'QF QD ',
0 1 2 3lC ! r ,
Scale(meters)
One superperiod of the ALS triple-bend achromat lattice contains
three combined-function (bending and focusing) magnets (B), six quadrupole
focusing magnets (QF and QD), and four sextupole magnets (SF and SD).
= 84
ALS design: 3-d CAD*I
example:storage-ring sextupole magnet
* CAD: computer-aided design
_5
CAD DESIGNED ALS HARDWARE
The following photos show:
1 ) CAD drawing of ALS storage-ring sextupolemagnet and vacuum chamber.
2) Engineering model of sextupole magnet.
3) One-half of storage-ring sector vacuum chamber.Each half of chamber is machined from analuminum billet, then the top and bottom arewelded. There are 12 sectors irl the storage ring.
4) First article (prototype) of completed sectorvacuum chamber. Recessed cut-outs make roomfor storage-ring magnets. Titanium sublimationand sputter ion pumps are mounted below thechamber. Devices on top are actuators for photonstops that prevent synchrotron radiation fromreaching the walls of the chamber.
85
88
89
i
9O
SYNCHROTRON RADIATIONSOURCES
The following illustrations show:
1 ) Sequence of diagrams shows the three main typesof synchrotron sources (bend magnets, wigglers,and undulators) and their spectral characteristics.
2) Diagram shows the features of a permanent-magnet insertion device and points out thedistinction between a wiggler and an undulator.
3) As the peak magnetic field increases, an undulatorrather quickly becomes a wiggler.
4) Drawing shows the mechanical structure that willbe generic for all ALS insertion devices.
5) The wiggler on Beamline 10 at tlm StanfordSynchrotron Radiation Laboratory was built byLBL and has many of the features that will be partof the ALS insertion devices. It has 16 periods oflength 12.85 cm and produces a peak field greaterthan 2 T.
6) Lombard _Street in San Francisco may be theworld's first and/or largest undulator.
91
Pole tips
Permanent magnets
Electronbeam
Photons
wiggler• non-sinusoidal orbits> harmonics• incoherent sum of intensities
undulator• sinusoidal orbit
• interference--> spatial and frequence bunching• coherent superposition
93
94
95
i
96
97
"_r, Jl rllllr' ' _1 _t
TECHNICAL CHALLENGE OF ALS
BEAMLINES
ALS
• Need to maintain photon source characteristics
in transport i_, high vacuum to experiments
• Photon delivery systems require
- mirrors
- focusing devices
- wavelength selection
• At these wavelengths
- refraction is negligible; lenses are useless
- efficient reflection only at 5mall glancing angles
° Therefore ALS optics based on glancing-incidenceoptical systems
• Also, development of microfabrication technique_permits
- diffractive structures, including "zone plates"
- multilayer for normal-incidence optics
• Power density can be severe
- several kilowatts/cm 2
• Optical elements must be cooled in high vacuum
- to dissipate power
- preserve surface quality to 5 microradians
98
ALS BEAMLINES
The following illustrations show:
1 ) Mirror designed and built at LBL to tolerate highfluxes of x-rays without thermal distortion.
2) The V[_ branch of Beamline 6 at SSRL, designedand built by LBL for high fluxes of wigglerradiation, contains many of the features plannedfor ALS insertion-device beamlines, including awater-cooled spherical-grating monochromator.
3) Proposed ALS beamline for x-ray imagingincludes the possibility of a vertically deflectedbeam that would illuminate an x-ray microscopewith a horizontal stage of the type biologists areused to.
99
lOO
i01
1'3".
ALS INSERTION DEVICES
Designation U means undulator; W means wiggler.The number is the length of the insertion-deviceperiod in centimeters. Undulators are about 4.5meters long; wigglers are about 2.2 meters long. Thefollowing figure shows the spectral coverage of theALS insertion devices and bend magnets.
1.03
XBL 893-5810
The ALS will produce bright beamswith undulators and wigglers, coveringa large spectral range.
104
The Advanced Light Source:
New Capabilities, New Research
ALS
, Next-Generation VUV Synchrotron Radiation FacilityOptimized for Insertion Devices
° Biological imaging
° INTENSITY, • Measurements on small or
"BR IGHTNESS" dilute samples
• Studies of ultrafast processes
"- • LASERLIKE COHERENCE
i • Studies of dynamic processesin biological systems
• SHORT PULSES (30_rilli3nths of a second)
• Bond_selective chemistly
• High-spatial-resolution
• TUNABILITY studiesi
• Lithography for chip
fabrication
Some "sci'entifi'cand"• echnoiogical areas that
will benefit:MATERIAL SCIENCES:THIN FILMS, SURFACESand INTERFACES
ELEMENT SENSITIVE BIOLOGY
CHEMICAL KINETICS andPHOTOCHEMISTRY
ATOMIC and MOLECULARSCIENCE
X-RAY LITHOGRAPHY andNANO STRUCTURETECHNOLOGY
t06
II I
J_ i,ll
I _t !_L-->-i T >
__-> _I!i]_:i , i_!!_ill->o_I :t_t I J • I.. _!i_i!?!
• _ _ ....................................................++-•...............I................................_ ;_ii__,_i_i_i__{"-/-- _t z .ii. i?ii_i'_i'-
!• • i
0
o "..C
_ F,"
t
107
SCIENTIFIC PROGRAM: ANTICIPATED EXPERIMENTS
ALS
U 8.0 8-(1000) eV _ chemistry and atomic physics
- high-resolution spectroscopy
- structure of actinides
U5.0 50-(1700) eV - materials and surface science
- high-resolution spectroscopy
- core-level spectroscopy
- surface EXAFS
- XANES
U3.9 170-(2100) eV - microscopy forlife and physicalsciences
- holography
- imaging
- structural biology
W13.6 1,000-20,000 eV - materials and life sciences
- small-crystal protein
crystallography
- surface EXAFS
- microbeam EXAFS
- atomic physics
Bend Magnets <1-10,000 eV - ultra-l_igh-resolutionspectroscopy
- variable polarization
experiments (e.g., circulardichreism in biological systems)
108
High-resolution measurements
High-resolution experiments are possible withspherical-grating monochromators
• recent result from BL-VI at SSRL
• resolution of 60 meV
_-- " T T _ T i ! i .,,. T T ,n
1.0-
- N20.8"
•_ _., C: -
(_
c: 0.6 - _ ls_ _ " -¢_, jl
0.4-
rr"
0.20.0 ' ! ' '400 401 402
Photon energy (eV)
x_ray absorption spectrum of gaseous molecularnitrogen, showing vibrational structure of ls-_"electronic transition
109
Element-specific imaging
• absorption.coefficient shows "edges"corresponding to photoelectron emission fromatomic shells
LLz
totalK
• contrast can be enhanced by measurementsabove and below the absorption _dge for aparticular element
• "water window" allows possibility of imagingbiological materials in aqueous medium
ii0
112
The ALS is well suited to chemistryand atomic physics
"='RbSr" _'"Y" "Zr--_'"Nb_"Mo""Tc Ru Rl_ Pd Ag Cd ,!n ,SnISb Xe
M--WaZ W _H_ " El '_VlBIT' _ nll'_/lr rl_ lm o Po "At _qnCs=.Ba "La_ Ta Re es i_p_ r_i_u_ Rg, '_r_ Pb, _a, :" o,.,.,,,_=.4,.,mo.,,uro.m=,mu ,,,=_,,s.o_,,=.=,_,_.=71 =_.._.(=,o_(=,o)_=_
Participating Research Teams will work with the ALSstaff to design, construct, commission, and operateexperimental facilities (insertion devices, beamlines,and end stations). In return for their effort, PRTs willgain privileged access to the facilities they helpdevelop. The following table lists the ix_ertion-devicePRTs that have been approved after an initial Call forProposals in March 1989.
115
_
=
ALS Insertion-Device Teams
Undulat0r SpokespersonsType and Alternates Science FocusU10 Tomas Baer (U. of N. Carolina) Chemical Dynamics (associated with
Yuan Lee (UC/LBL) the Combustion Dynamics FacilityAndy Kung (UC/LBL) initiative) '
U8 Denise Caldwell (U. of Central Atoms, Molecules, and Ions' J
Florida)Manfred Krause (Oak Ridge Nat.
Laboratory)Norm Edelstein (LBL)
U8 Vic Rehn (Naval Weapons Center-- Dynamical Studies of Materials .......China Lake
R. Stanley Williams (UCLA)Marshall Onellion (U. of Wisconsin)Richard Rosenberg (U. of Wisconsin)
Jory Yarmoff (UCR)U5 Steve Kevan (U. of Oregon) Materials Sciences (NSF Science and
Technology Center) ,,,
U5 Joachim St6hr (IBM Almaden Surface and Interface SciencesResearch Center)
Thomas Callcott (U. of Tenessee)
Franz Himpsel (IBM WatsonResearch Center)
David Ederer (NIST)U5 ' Brian Tonner (U. of Wisconsin) Surface and Interface Sciences;
Steve Kevan (U. of Oregon) Spectro-MicroscopyGiorgio Margaritondo (U. of
Wisconsin)
Marjorie Olmstead (UCB)U3.9 Steve Rothman (UCSF/LBL) X-Ray Imaging and X-Ray Optics for
Dave Attwood (LBL) the Life and Physical SciencesMalcolm Howells (LBL)Richard Freeman (AT&T)
Janos Kirz (Stony Brook)Wiggler Bernd Crasemann (U. ot Oregon) Atomic, Molecular, and Optical
13.6 Phil Ross (LBL) Physics with X-Rays; MaterialsDennis Lindle (NIST) Science
Chuck Fadley (U. of Hawaii)
Wiggler Alex Ouintanilha (LBL) Life Sciences13.6 S.-H. Kim (UCB/LBL)
Mel Klein (LBL)Linda Powers (Utah State Univ.)Steve Cramer (BNL)
- photoionization, absorption, fluorescence- primary dissociation- molecular and metal clusters
- double and triple ionization- dynamics of excited states (pump-probe)- radicals and transient species
• key participants:
Baer, Lee, Kung, White, Berkowitz, Houston,Ruscic, Snyder, Hepburn, Moore
1
i
. 119
FURTHER INFORMATION ABOUTRESEARCH AT THE ALS
° ALS mailing list
* join or form research team (see me)
• ALS Handbook
* ALS Users' Meeting: August 23-24, 1990 at LBL
120
FRINGE BENEFIT
The scenic beauty and temperate climate of the SanFrancisco Bay Area come free of charge to thoseworking at the ALS. This January 1989 photo, takenfrom a hill behind the ALS, shows the brightly litconstruction site against the backdrop of a wintersunset.
1. Surface and Interface2. Extreme Environment3. Phase Transition
4. Electronic Prope .rty of Solids5. Chemical Reaction (Chemical Crystallo_aphy)6. Atomic Physics7. Protein Crystallography8. Macromoiecular Solution and Muscle9. Medical Application and Diagnosis10. Actinoids11. Nuclear Excitation12. Nuclear Resonance Scattering13. Ma_etic Scattering14. Inelastic Scattering15. Photoacoustic Spectroscopy16. XAFS17. Topogaphy18. Diffuse Scatte_ng19. Extremely Small Scattering20. Trace Microanalysis21. Soft X-rays (Microscopy)22. Soft X-rays (Photochemistry)23. Soft X-rays (Solid State Physics)24. Infrared Spectroscopy
143
Photoionisation of Ions _nd the General Program in Atomic and Molecular,Physics at Daresbury
J B West, Daresbury Laboratory, Warrington WA4 4AD, UK
To date the only cross section measurements made on atomic ions o'iginatefrom the joint programme between Newcastle University and DaresburyLaboratory a few years ago. Yet from the theoretical viewpoint, and for anunderstanding of loss and confinement processes in, for example, fusionreactors, they are in great demand. The problem lies in obtaining a wellquantified atomic ion beam, of sufficient density that the photon flux willallow reliable m,easurementsto be made. For calcium, strontium, barium,zinc, gallium and potassium ions this was achieved at the Daresbury SRSusing a merged beam technique, where a well collimated light beam wasmerged over a length of about 10cms with the ion beam as shown on figure 1.
' 0
Figure 1 (For an explanatlon of the symbols, see Lyon et al[l])
._.1 11I I1 _ rlil , l't,i
--r- , , _ Figure 2, taken from Lyon et al[l] wherethe experimental procedure is also
nI t described, shows the precision obtainablefor Ba+ in the region of the Sp- 5d
_I resonance Absolute cross sections with an11 -
II accuracy of --_+12%were obtained, where
t! ali the absorbed photon resulted inenergy,, I the production of the doubly charged ion.
"; It'... { Tlne technique could meas,,re cross• { I sections down to -..10"17cm2, assuming an" I f /k! incident photon flux of 1012photonslsec,
I ,} /i \ and this limitation prevented useful
[ _ 4¢/t \, quantitative measurements being made on\ other singly charged ions.I k,
.; ".,.. With only minor adaptation, this equipmen_
I 1 I could be used to detect higher charge
Figure 2 Total cross section of Ba+ in the region of the 5p - 5d resonance
144
states resulting,from the ionisation of singly charged ions, with the interestnow moving to ionisation of deeper inner shells and core levels. Aparticularly interesting case is magnesium, an important element in stellaratmospheres and tractable theoretically. However, this means partitioning ofthe cross section since higher multiply charged states are accessible, withconsequent lower count rates in any one channel. For this reason a photonflux in the region of 1014photons/sec is required in the grazing incidenceregion of the spectrum; the monochromator output must be substantially freefrom higher orders and stray light, and this implies low efficiency. This isbeyond the capability of today's conventional storage rings and will have toawait the very high intensities available from a source such as the APS.
The current programme in Atomic and Molecular Science is focussed onphotoionisation of atoms and small molecules. On the atomic side,experiments on the double ionisation of helium were completed recently[2],verifying the Wannier thresl"old law for double photoionisation. Also, theangular distribution of the electrons has just been measured, and theseresults show a marked divergence from theoretical expectations. Otherexperiments include fluorescence polarisation measurements for the atomicions calcium and strontium, which, when combined with photoelectronangular distribution measurements, form the complete photoionisationexperiment. A sizeable part of our programme is devoted to studyingmolecular fragmentation. The triple coincidence technique, in which the twofragment ions are detected in coincidence with the photoelectron after tileparent molecule has been doubly ionised, was developed at Daresbury[3], andexperiments in this area continue with the addition of fluorescencemeasurements.
Photoelectron spectroscopy continues to be used as a basic technique;prominent among experiments in this area is the joint NIST/ANWDL project,using a high resolution angle resolving system shown on figure 3.
This system, designedand built in the USA, hasbeen fitted to the highresolution 5-metrenormal incidencemonochromator at the
C 'le
"' ""' _ Daresbury SRS andL
"" _c = produced precision,,,_ _'" bench-markmeasurements on a
o, _,,,,,,,.,_ number of small_.1 O_ _m_:f_'vaqrtet-I Ir_4_l£S'I Lrkrc'tr_ _(trqm_te-I II=NI
__t.
FT _ hrmmt'm _'_d_.n
1
Figure 3
145
- _
Figure 4 shows the angular distribution parameter for the v=l vibrationalmember of the N2+ X state, in the region of complex autoionising structure.
The assignments shown are derived from earlier experimental work and mayhave to be changed as a result of these measurements and recent theoreticalcalculations; full details are contained in West et al[4].
z.o- Precision
ta measurements have,,., also been made on the
1.6 _., _I, molecules 002 and H2.• _ _,Z Pl71
tL. _ I _- i ,,.*'_ 1 '"' The data for CO2 are
II c,,., '" being analysed
" 1.0, [I}_,-._ _ ',l'i _4o ,,,o '.,._JT" t.,.z3 _"_ Iz _,,.zJ,, i _ 7._,/ _ assuming three
=" ,/ _1 c,,.oJ'_I [ Jll vibrational modes arei ,._'_ I l , ,,_ 1_,, present: symmetric
, stretch,
0J, ,i _ _'_l't"J_t/l__', _t1_t '_t antisymmetric stretcho.: _ i and bending, and theo.0 ,, ,,,.,-- data set for this
Figure 4 The angular distribution parameter for the v=l member of the
ground state of N2+.
"t the X-state threshold to beyond the- B-state ionisation potential on a..i photon energy mesh of 2meV. Figure
ii t 5 shows a comparison betweenresonant and non resonant
_.t ]l_j_l behaviour, where the photoelectront spectra indicate the presence of." I _..---- .,L......._..___._._.....__ higher vibrational modes for the' ....... " resonant case.
-. In tiqecase of the H2 experiment,"" angular distribution measurements
,- were made in regions where_" vibrational autoionisation takes
i ,." place, close to the thresholds of
- the rotationally split H2+
i i .__---_ _L [ vibrational continua. By this means-_----- I rotational infcrmation can be, _-
................. obtained, without the requirement
Figure 5 "On" and "off" resonance CO2 photoelectron spectra.
for rotational resolution in the electron spectrometer. There have long been
146
theoretical predictions for this effect, and confirmation has had to ,waituntil now for an experiment with sufficient precision.
Looking to the future, the atomic and molecular science programme atDaresbury will move closer to applied science areas, with metal c!usters andtransient species becoming more prominent. Much of this work will require a
source with two to three orders of magnitude advantag_ in photon intensity
over the SRS, and a design study is presently unGer way for a VUV/Soft X-raysource to meet these requirements.
References
[1] I C Lyon, B Peart, J B West and K Dolder J Phys B19, 4137 (1986)
[2] G C King, M Zubek, P M Ru_er, F H Read, A A MacDowell, J B Wes_ and
D M P Holland J Phys B21, L403 (1988)
[3] L J Frasinski, M Stankiewicz, K J Randall, P A Hatherley and K CodlingJ Phys B19, L819 (1986)
[4] J B West, M A Hayes, A C Parr, J E Hardis, S H Southworth, T A Ferret't.
J L Dehmer, X-M Hu and G V Ua_r Physica Scripta (in press)
147
Research with Stored Multi-Charged lons at the APS and the NSLS
Churchl,*'_ _ I 2 2_. D. _ravis, B. M. _ohnson2, M. Meron , K._W. Jones ,D. A.
I. A. Sellin_,_J. Levin-, R. T. Short-, Y. Asuma4, N. Mansour-, H. G. Berry-,: and M. Druetta b
•Invited speakerI. Physics Department, Texas A&M University
: 2. Brookhaven National Laboratory3. University of Tennessee and Oak Ridge National Laboratory4. Argonne National Laboratory5. University of St. Etienne, St. Etienne, France
ABSTRACt
Potential ion beam and stored ion t&rgets for research using synchrotron
radiation from the Advance Photon Source are discussed. The difficulties of
cross section measurements for the photoionization of ions with high charge q
and atomic numler Z are mentioned, but preliminary observations of photoionization
of stored Ar2+ and Xeq+ (4 _ q _ i0) are described, and a brief discussion of
•the measurement technique is nresented, with reference to improvements possible
usir_ undulator and wiggler radiation frcm the APS.
Earlier presentations at this workshon have nrovided extensive motivations
for research on multi-charzed ions, among other targets, using synchrotron
madiation from the Advanced _oton Source. We note only that charge state
distributions re_sultin_from vacancy cascades following inner shell photoionization
_,_atoms have be_en studied only for a few ta_]_ets,while similar
v_cancy cascades Ln ionic ta_ets bravenct been experimentally addressed at all.
However, some caiculazions for -he ions cf iron have been carried out. To study
such systems, and to measure cross secticns for the nhotoionization of ions, dense
ionic targets 'mirha range of charze states c emd atomic number Z are desirable.
Among the most iLk.elycandidates are_a ccntinuous ion beam from an Electron
have pr<duced be_mnswith charge states as high as _r16+ and with beam currentsQ+
exceedLng I00 micro_mperes for _r _ . Thus, mon densities near 106/cre3 are feasible
with typical source parameters such as a !0 mm diameter apertume, I00 mm-mrad
emittar:ce,and !0 ,.7extraction. Significant imnrovements in ion densities
would be possible, if tighter beam focussLng were to become feasible. (lt is
assumed here that a beam waist ccmnarable to the diameter of the source aperture
-- _ _ _'_7_I _m_7_I_. ]
]48
Alternatively, a Penning trap cmn he used to hold ion targets produced by
electron impact, photoionization of neutrals, or other means. Preliminary
analysis of results from measurements at the NSLS, intended to demonstrate the
photoionization of ions by this method, are now nresented. _lotons from
unmonochromatized bending magnet radiation from the NSLS were focussed near the
trap center by a cylindrical mirror with 4 mrad horizontal acceptance. The
photon bemn was blocked by a fast shutter, as needed. The "white" radiation
was filtered only by a Be windon before the trap. The transmitted beam flux
was monitored with an ion chamber.
lons stored in the trap were detected on a charge/mss ratio basis by
resonance absorption of rf enerzy by the axial oscillation frequencies of the
. Ar 2+stored ions For mea_nmrementswith an target, electron impact ionization
of a "puff" of argon gas into the trap vol<_e f_n a fast valve was used.
The ions were stored for two seconds_ to permit the target gas to be largely
" pumped away, and then a pulse of synchrotron radiation irradiated the stored ion
target. The resulting ion si_nals were detected, and the ion sample dumped
preparator%'to background measurements. Background ions arose from two sources'
one was stored ions other than Ar 2+ produced by the electrons, and the other was
photoionis produced by ionization of the residual target gas. These backg_rounds
were removed by two cycles similar _o the "signal" cycle just described. In the °
second cycle, no electron pulse was used, yielding the back4_roundphoton signal,
since no targ_etions were present. In the thimd cycle, no photon pulse was
employed, yielding the background from the electron pulse, since no photoionis were
produced. The multi-charged argon ions remaL]ing alternsubtraction of these two
backgrounds were interpreted as the net signal from the Ar2= photoionization. The
average of a nmnher of these triple cycles yielded a net multi-charged ion signal,
with a peak height distribution significantly different from the distribution
t-ypicallyobserved when photoionizing atoms.
The successive photoionization of stored Xeq_ ions was s_died in a similar
manner, but in this case synchrotron radiation was used to nroduce the sot-redion
tarzet, as well as to ionize it. In these measurements the photoionization of
residual Xe atoms durimg the part of the cycle cycle followir_ the gas puff
prodtJcedmost of the bao_kground, in a distribution of charge states. A net signal
of highly charged ;<eions was found. In these measurements, target densities ne_m_
107/cm3 for _r2+ and 5 x I05/¢_n3 for the Xenon ion target were estimated
-
i49
_
In conclusion, net ion signals from measurements designed to observe
the photoionization of ions stored in a Penning trap have "been observed: With the
_creased flux of synchrotron photons potentially available from an }hnS
wiggler or undulator, both ion target densities and photoionization rates for
the stored ions should be increased by an order of mangitude or more. A band-
width of 10% is provided by the unfilted undulator r'adiation, which .nan be
reduced to about 2 % b y a pJJlnole paerture, is also attractive. Since ion
densities similar to those in the traD are available from ECR beams, and sit,ce
particle counting is available without the trap magnetic field (which will
increase the sensitivity over the analog detection by a factor of 143 or so), rbe
future of photoionization studies on ions cannot be dismissed.
150
Multi-Charged Ion Research Using theAdvanced Photon Source
/ • I lIJL1_l ILIC;]LI I I_.,_(;;_ILI %,*I I /-Ikl I_'C;;IL,_._
2. APS beam properties and ionic targets
3. Photoionization of ions at the NSLS
151
M5
M4MsM2M1
E3
L2
LI
K
KrFig. 1. Typical example of the vacancy cascade for
filling the initial K-shell vacancy of Kratom. The solid circle indicates the electron
and the open circle represents the vacancy.Arrows show the direction of the vacancycascade.
Table I. Relative abundance of ions resulting from an inner-shell
vacancy of Ar atom with and without electron shakeof[.
K La Lt L=Charge
A B A B A B A B_
I 0.7 0.9 0 0 0 0 0 0
2 8.6 11,2 3.7 4.4 85.0 100.0 85.1, 100,0
3 10.3 10.3 82.5 95.6 14.8 0 14. 8 0
4 43.2 53. 1 13.6 0 0. 2 0 0. 1 0
5 26.1 18.6 0,2 0 0 0 0 0
6 9.3 5.9 0 0 0 0 0 0
7 1.6 0 0 0 0 0 0 0
8 0.2 0 0 0 0 0 0 0
A : With shakeoff.
B : Without shakeoff.
( 376 )
Bulletin of the Institute for Chemical Research,Kyoto University f_., 373 (1985)
152
From Phys. Rev. A .3._4_,216 (1986)
28 I I 1 I I I I I.....
24
3p4
3p
0- 0 4 8 12 16 20 24
INITIAL CHARGE Zi
FIG. 2. The mean final charges (Zr)resulting from the cas-cade decay of single inner-shell vacancies which can be createdin the various nl subshells of iron ions with initial charge Zi.
153
MULTI-CHARGED ION TARGETS
(1) Ion beam from ECR ion source
Example: PIIECR @ ANL
601_A Ar8+ beam at 10kV x q
Assume crossed beam geometry,focus to 1 cm diameter spot
Then n = 106 ions/cm3
(2) Ion trap
Stored densities of cool, singly-chargedions = 107/cm3
... expect n = 107/q ions/cm3 at best
154
ECR Source
Assumed emittance = 100 mm mradSource diameter = 10 mm
BEAM WAIST10mm
ION _ ' 20mmBEAM
dL. 1m --,i-"
=. 106/cm 3 for 501_Aof Ar9+nmax
Undulator A beam spot @ 60 m from ring = 2 mm x 0.75 mm
Wiggler A beam spot @ 60 m = 120 mm x 0.75 mm= (2 mrad horizontal)
- Wiggler A, unfocussed, with 0.25 mrad horizontal fan ofradiation, in = 4 keV bandwidth --> = 3 x 1016 photons/s
Undulator A, 10% bandwidth --->= 2 x 1016 photons/s
Undulator A, 2% bandwidth with pinhole --> = 2 x 1015 photons/s
=
155
iii0 i,,,,
• / (..4"" .-'"_L.'# .-" °•' . S X
• i ,./_ /. =!//;
• ti .'i! ':°,,J S I
: II i Iii-;ii l i o
, " , , o,l ; t u
,. .i < >_ t"i , E' ; ' I i
' , I _-_'o '_ c_
' ' I << E El._''ii I _ "_ii ' E_°o°>", | I2_ i,.I
.{:1' °° ° -i", ' "" "" <"
', I >> £5_ _i <
1 I I"- _'-,, ""_ _, t _._.__ x - ,
I"l 0..
i t <<Oco' t i
. : , I I ¢1 iii|
i I I I : , iii' : ' i I O_ I._: ii ._ :)
' i, :1 : , , I :lo
ti l ' <,,: ' li o _
..... l, I !, _i,,__...... ,i,..}iilil I i ! |is. ii ! • • |lliil i . I i |iilll i i ii_ |11111 1 I • _ _
lx_ _ L'_ 04 _ -0 ' _ 1,,,
0 {:_ 0 C:) 0 0 <:D _ u
(P_X_/A&H%['O/s/qd) xnL4 =0
o
156
Photoionization cross sections at K edge
(1 0-20 cm2/atom)
Argon Z=18 EK=3.2 keV _K=7.2
Cu Z=29 EK=9 keV (_K=1.6
Ze Z=40 EK=I 8 keV _K=0.43
S n Z=50 EK=29.2 keV _K=0.17
W Z=74 EK=70 keV _K=0.05
From Storm & Israel, Nuclear Data Tables AI, 565 (1970)
157=
1618- u-
o4 2 -EO
ZOF-o 1619--UJ0")
rf)cD0Eli0 5--
10-20 I I ! I . I1 2 5 10 20 50
PHOTONENERGY(KEV)
t58
159
Ion confinement, photoionization of ions, and low energymulti-charged ion collisions at X-26C, NSLS
Figure 13. Multiplet structure in atomic manganese arising
from photoionization in the 3p subshell
192
isoelectronic series. Would this effect be as pronounced for Ai"TM as for Be'? In the second example, 1°
the 3p photoelectron spectrum of Mn (Fig. 13) reveals strong intershell correlation of the type 3p z
3s3d and it would be instructive to compare the 3p spectra of Zn s+ and Kr 11. with the Mn spectrum.
Finally, emission experiments of this nature could also address wave function collapse when apprt_ching
d and f transition "_ 'scn!..s, however, in these latter cases the crucial answers are likely to ce,mc fmna
experiments done at lower photon energies.
Let mc now make an exmt_.rsioninto x-ray spectrometry. Nearly 20 years ago wc posed thc: question
whether so-called x-ray diagram lines, Ka, la, etc., are pure lines according to definition, n_lmcly Kcrl
= K _ L3, or whether these lines arc contaminated by parasitic satellites of the type KM _ L,M,
KN _ L3N, etc. This problem is akin to that discussed earlier for the Auger spectra, but it is
exacerbated tbr x rays because of thr _smaller shifts occurring between the lines of dil'fcrcnt origins. For
L x rays of a number of elements, the illusory nature of diagraln lines observed under normally
prevailing excitation conditions has been demonstrated in a few studies, but merc extensive v,,t_rk, iiided
by a strong tunable excitation source, is needed to be able to dctermine such basic quantities _s n_tural
line widths and absolute transition rates pertaining to a single hole state with an accur_lcy of better th¢ln
20%. Figure 14 presents a schematic illustration of the situation al hand as well as an experimental
method to disentangle the components. 1_ A conventional measurement of the Pb La_ x rliy yields a line
of 8.5 cV width (FWHM). If the La_ line is placcd into coincidence with the Ka_ (K - L3) line
following K ionization then a line of 6.5 eV width results. This is, indeed, the pure diagram line La_
(L 3 - Ms). The answer to the origin of the pseudo diagram line comcs from the coincidence with the
Ka, (K - Lz) line. The resulting line is offset from the true I..a_ line because it is a satellite L,N - NlX,/Jls
following the CK transition L2 - L3N, Under normal excitation modes, ionization takes piace in _lll L
subshells ultimately creating a complex "I.a_" line. The contamination of the I__ line by parasitic lines
has been investigated in detail for Zr. _z As seen from Fig. 15, the purity of the La line is generally less
than 75% and may drop below 50%. Both Ck)ster-Kronig transitions and shakcol'f processes contribute
to this effect.
Amor_g other applications of hard photons in atomic processcs (at thcsc energies princesses arc
essentially atomic regardless of the state of matter), I shall select a last one: that of the photoelectron
angular distribution and the effects of retardation. This is one of the more intriguing research, although_
:" its beginning goes back, once again, to the Wilson cloud chamber plates taken by P. Anger - and shown
in Fig. 1. In fact, the long tracks seen in Fig. 1 were the initial object of that study with the aim to
distinguish between the old and the new quantum theory by way of the angular distribution of the
photoelectrons. The work of the time relied on hard x rays in the range for which the APS is designed.
Due to momentum transfer, or retardation as we now prefer to say, the angular distribution is skewed
193
,0 - l
-,Oev E0 '0 -'0 [ 0 ,0 "_0 -qO ,_'g ,')ev
........, Ii 'I 2'_e STE D I I ?,_d STE;_'
_t STEP I I I
l II SAT. II Sir, III SIVlV"'*" t_''_''" t"*" _'°"', _. _. •
,_ACANICY SINGLE _OU_LE DOqJl_.E _ 1 IllPt..E DOUBLE InlPLE
/(Figure 14. The isolation of a pure diagram line in an arbitrary
case and in the case of the Pb LcKI x-ray line
hVPHOTON ENERGY(keV)L. 6 B 10 12 1_, 16
100T.... I '_ _ " _ ' : ' 1 . _ ' i
/ Zr L'%,2
/
..c_50
u ,..,/ TRiPL__ .-......-.---..---- "- "---
0 OS _ 15 2 25iNITIALVA_CY DISTRIBUTION L_,'(Lt',-LI}
Fi_lure 15. The composition of the Zr L_ x-ray linephoton-excited in the energy rangebetween the LI and K shells
194
Abb. 25. R.lchtun_eiluu4_ _ WK s in Argon. (NachAuosn;. Kurve berer.hnet nsr.h ¥xscn'tn.)
Figure 16. Skewing of the angular distributionof K photoelectrons in Argon
II. K. 'I'SI'_N(;, R. II. PRATT, SIMON Y U, ANID AKIVA lION
From Phys. Rev. A 1_Z7,1061 (1978)i2
_. U K " shell
: ooo5 ,_,J l'_,}_ 1332wev J- Io--O\ Pb K-shell
" .'_,_ -,-.,._,_ o ii m .__
O 30 60 O 30 60 O 30 60 90 120 150 180
8 Angle (deg)
(o) (b) (c)
Figure 17. The asymmetry of photoelectron angulardistributions in experiment and theoryfor three cases
.=i
195
forward as clearly evidenced in Figs. 16 and 17. Early calculations of the Sommerfeld school were in
good but not perfect accord with experiment for the K shell, and because of their approximate nature
in only fair accord for the L shell. 1_ More sophisticated calculations TMof the recent past gave improved
agreement with the body of experimental data existing at higher photon energies and, significantly, with
the few data available at low energies. This is shown in Figs. 18 and 19. An iselatcd study _sexists for
the M shell, that of Kr. In that work, the three subshells, s, p, and d, could bc distinguished and wcrc
shown to exhibit quite different angular distributions for the respective photoelectrons, but in satisfactory
agreement with theory. In particular, it was found that the 3d electron distribution was skewed tbrward
while that for the 3s electrons which have similar energies is almost symmetric, about 90°, indicating
that no higher multipoles beyond the dipole operator are active. Although there is a rudimentary
understanding of the higher multipole effects in angular distributions, we should remember that there
is only one experiment tbr shells higher than the K and L shells and very few cases in which the L
subshclls were distinguished. At the same time, _eccnt more elaborate calculations make some
unexpected predictions, especially near inncrshell thresholds. '6 This is an area where much work remains
to bc done over a wide range of energies, elements and subshells.
In the past, ali experiments were carried out with unpolarized radiation and this is reflected in the
plots of Figs: 15-19. With the polarized radiation emerging from a synchrotron radiation source,
detection of the higher multipoles arising from the e _u term requires a measurcnlent in the XZ
coordinates '7 as sketched in Fig. 20, where the complete expression for the angular distribution is given
ft_r the case that both the dipole and quadrupole operators contribute. TM Three cocfficicnt,; of the
t.orrcsponding Legendre polynomials enter the expression which is derived tk_ra polarization of 100%.
A more wieldy expression would apply to partial polarization of the photon beam. Fortunately, the
insertion devices which are an integral part of the new, third-generation synchrotron radiatk_n sources
yield a virtually complete polarization, of the photon beam, 99.6% as measured in one case, so that data
analysis is simplified and a high accuracy is obtained as demonstrated in Fig. 21 for the Bz dipole-
related/3 parameter in the case of He at low energy of photons emerging from an undulatc_r.
With this glimpse into the future and the promise expressed in several results (e.g., Fi3s. 5 and
21) that wcrc obtained on the way to the new advanced photon sources I like to conclude this
presentation, but not without cautioning that the increased power and energies of the advanced light
sources must be matched by improved users' apparatus to optimize the opportunities.
196
OerNLo0tll lt- 4_1t4@
I ' 1 on_.- owo It-iSH|
Ill K(WM a) Ne K(AI Ko) Nelll(M4l Ko) I 1
90_llV -- 61711V 38i41N -] i KrMIIMqKo) Kr MI_3(MqK o) KrM4s(MIIK(II)_ " ...... L ....... ',..___.__............. Z--_.___/
i-,Z Z I .......................
- . _.. - i(o )_i
ENERGYENERGY 120 r
lO0 :"- ._ _ I00
/ f
40 ! i - _ _.#_,_ -- _ z
_,oi/ / X X. ,,,_,o I 7f ,_-_,,+---d,'t-.......... -'_--'_<iii" _ /_'l '_Xl_ Kr M,(Mg Kel)_, //"__\, J ._,o.... :_ ...................,.,_,,..o
._4, ii. . _, | I!l_i,l|__ _NilIIWMo) "l"4u_, '_/_ ...... "--_4B,,0.237 "-i /.# SOL;D LINES; "\'_ I t
i _ SOLIOLINES: lt ,l_ #J'_ Jie,A,Oil'l'Aie sin:' # '_ I
0 30 60 90 IlO _50 iso 0 ] 0 60 9O *20 (._0 _80
_.,,_NGLE (deq) _},ANGLE (_leql
Figure 18. The effect of the eik'r Figure 19. As for Fig.18 but interm in the angular dis- the case of Kr M Shelltribution of photoelectronin Ne K Shell
x
• h- " >Figure 20.
(Note: the angle@ _- _ .._._ #/corresponds to 0 il_ rp#t t kin Fig. 16 andO
3. W. Mehlhorn in Atomic Inner-Shell Physics, Plenum Publ. Corp. N.Y. (1986).
4. Atomic Inner.Shell Processes, B. Crasemann, editor, Academic Press (1975);
S. L. Sorensen, et al., Phys. Rev. A3___99,6241 (1989).
5. H.W. Haak et al., Phys. Rev. Lett..41, i825 (1978).
6. M.O. Krause, J. Phys. Chem. Ref. Data 8, 307 and 329, (1979).
7. G.B. Armen et al., Phys. Rev. Lett. 54, 1142 (1985).
8. T.A. Carlson et al., Phys. Rev. 15__.!1,41 (1966); M. O. Krause and T. A. Carlson,
Phys. Rev. 15.__.88,18 (1967).
9. M.O. Krause and C. D. Caldwell, Phys. Rev. Lett. 5..99,2736 (1987).
10. J. Jimenez-Mier et al., Phys. Rev. A4___Q,3712 (1989).
11. J.P. Briand et al., in Proceedings of Int. Conf. on Physics of X-Ray Spectra. NBS (1976), unpubl.
12. M.O. Krause et al., Phys. Rev. A__.66,871 (1972); F. Wuilleumier in Proc. Int. Conf. on X-Ray
Spectra, Univ. Miinchen (1973), unpubl.
13. W. Bothe in Handbuch der Physik vol. 23.2, Springer (1933).
14. H.K. Tseng et al., A1.__._77,1061 (1978).
15. M.O. Krause, Phys. Rev. 17._27,151 (1969).
i6. Y.S. Kim et al., Phys. Rev. A22, 567 (1980); A. Bcchler and R. H. Pratt, Phys. Rev.
A3____99,1774 (1989).
17. J.H. Scofield, Physica Scripta (1990), in press.
18. J.W. Cooper (Private communication).
Acknowledgemeat
Research sponsored by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S.
Department of Energy under contract DE-AC05-840R21400 with the Martin Marietta Energy Systems,
Inc.
199
Beam-Line Considerations for Experiments with Highly-Charged Ion_*
Brant M. JohnsontDepartment of Applied Science
Brookhaven National Laboratory, Upton, NY 11973
The APS offers exciting possibilities for a bright future in x-ray research. For example,measurements on the inner-shell photoionization of ions will be feasible using stored ionsin ion traps or ion beams from an electron-cyclotron-resonance ion source, or perhapseven a heavy-ion storage ring. Such experiments with ionic targets are the focus for thediscussion given here on the optimization of photon flux on a generic beamline attheAPS. The performance of beam lines X26C, X26A, and X17 on the x-ray ring of theNational Synchrotron Light Source will be discussed as specific examples of beam-linedesign considerations.
iwith K.W. Jones, M. Meron, M.L. Rivers and P. Spanne (Department of Applied Sci-ence, Brookhaven National Laboratory) W.C. Thomlinson, D. Chapman and J. Hastings(National Synchrotron Light Source Department, Brookhaven National Laboratory).
"Research supported by the Chemical Sciences Division, Office of Basic Energy Sciences,US Department of Energy, under Contract No. DE-AC02-76CH00016.
In Sep',ember of 1980 the "Workshop on Atomic Physics at the NSLS" was held ai,Brookhaven National Labcratory. Considerable interest and excitement was expressed for
the potential impact on atomic, molecular _,nd optical (AMO) physics research promisedbF' the new National Synchrot.ron Light Source t NSLS), which was then under construc-tion. Many of the conclusions and areas o," interest evidenced in the proceedings of thatworkshop are stiii true today. For examp',e, (1} the AMO physics community is muchmore intel, est.ed in soft-x and VUV photons, i.han in hard x rays; (2) there have been very*"ewmeasurements on the photoionization ef iGns, particularly for inner-shells', and (3)
; i.he next generation fa.cility will undoubl.edly enhance experimental capabilities in currentresearch programs and foster the development of new research endeavors.
_. ExperimentM progress in the decade since the NSLS workshop is well documented in" other contributions to this APS worksliop. Some of the specific experiments performed
on beam lines X26C at, the NSLS are discussed or mentioned in the contributions bF,)>ave Church, Bernd Crasemann, and Jon Levin. Some of this work was performed inoollaboration with ,esearchers from Texas A&M, the Universi,v of Tennessee and Oak
Ridge ?lat, ional Labor_'..tory, Argots.no NationM Laboratory, and St,. Etienne, FRANCE.AdditiorM studies of synchrotron-radiation (SR)induced fluorescence spectroscopy and
the direct inner-shell photoionization of ions from a conventional ion source are carriedout. by the local BNL group, but the)" will not be discussed here.
The rel_,tively small number oi practitioners in AMO physics wilh hard x rays is botha blessing and a curs¢. The good news is that the field is wide open with more excitingideas and possibilities than current researcbers can possibly investigate. The down side isjust that - ii. has proved difficult to interest o_her experimenters (and funding agencies) to
-I turn their attention toward hard x-ray research in AMO physics. Perhaps this workshop: wi!l serve as a catalyst to stimulate interest in the illuminating possibilities thai the APS,
the ESRF, anci the SPring-8 will offer.
o Unqu___tionably, the new tMrd generation hard x-ray photon sc.urces will provide sub-stantially mt_re x rays than second generation machines (such as the NSLS x-ray ring).However, experimental beam lines must be carcfully designed to realize the full potentialof a third generation photon source. Figs. 1-2 give an over-_iew of generic beam linecor, siderations.
The specific characteristics of beam lines X26C and X26A, with particular emphasison the performance of a l:l cylindrical focussing mirror, are discussed in Figs. 3-9. Therelativo perfocmance ,:ff APS undulator A and bending magnet beamlines ai. the NSLSand APS are co:npared iri 'Fig. l0 and dis,:ussed in Fig. 11 through the example ofmeasurements of the radiation produced by the NSLS superconducting wiggler on pori2X17.
_t
_l'he PHOBIS concept for producing highly-charged ions through successive photoion-izalion of trapped ions is reviewed in Figs. 12-13. Finally, an overview of a proposed
. !:eavy-ion storage riv.g for use at a hard x-ray light, source is given in Figs. 14-24.2
201
BIBLIOGRAPHY
ATOMICPHYSICS RESEARCH ON BEAMLINE X26C AT THE NSLS
B. M. Johnson, M. Meron, A. Agagu, and.K.W. Jones,Nucl. Instrum. and Meth. B24/25 (1987) 391.
Fig. 1 illustra.tes the relevant, parameters that determine the photon flux Nout(_) ava.ilable for= an experiment. In the equation given at the bottom of the figure; 8 x is the horizontal
divergence angle of emitted radiation from the bending magnet or insertion device ofinterest.
S
203
Nout(X)= N(X)0×TBTM
TO MAXIMIZE PHOTONFLUX FORASYNCHROTRONRADIATIONEXPERIMENT:
2. Design both beamlineandmonochromator to acceptLARGESTPOSSIBLESOLID ANGLES.
3. MATCH ACCEPTANCESof mono-chromator and beamline tothe emittance of the source.
4. MAXIMIZE TRANSMISSIONofbeamline and monochromator.
Fig. 2 describes the design crii.eria for optimum photon flux on a generic synchrotron radi-ation (SR) beam line. As the equation from Fig. 1 impt!es, the source photon flux,Ox, transmission of beam line and monochromator, and monochromator acceptancesolid angles should be maximized, while the emittcnce of the source and beam lineare minimized. A fuller desc,iption of this and other considerations are given in the
general references listed in the bibliography.
204
' I!I_
_ Fig, 3 is a schema.t,ic repret;_ntat, ion of the si,o:'age rings and bealn lines of t,he NSLS x-rayand VUV bea.m lines. The loca.t, ion of bear:': port, X26 is indica.t, ed.
Fig. 4 gives the layouts of beam lines X26C .nd X26A on the X26 t_eam port of the NSLS):-ray ring ai the NSLS, Note thai. r'either beamline presently has a, monochromator,but. that each has an x-ray focussing mirror, On X26(I a 1:1 cylindrical mirror is
located at, about 10 m from the photon source point t,o produce an image in theexperimental hut, cb at about, 20 m, On X26A an 8:1 ellipsoidal ulirror is posii, ionedai 8 m to produce a focal spot at about, 9 m.
206
X-RAY FOCUSSING MIRRORS
1"1 CYLINDRICAL
- 8:1 ELLIPSOtDAL
1"1
8:1
Fig. 5 shows the two focussing mirrors. The l'l mirror is made of Zerodur; is coated withplatinum; is 60 cm long; and accel_'_s 4 mr of horizontal radiation. The 8'1 mirroris :.;ade of elect.roless nic!:e!: is coated with platinum; is 20 cm long; and accepts 2
' ,, 1/
mr of horizontal radiation. __,'_h m,rrors are u',,.,u at an angle of incidence of about4 mr giving a high-energy cut.off at about 1,5keV. For a bending magnet or wiggler
,, at. the APS it might be desirable to try t,o focus the harder radiation above 15 keV.The cut.off can be moved to about 40 keV by lowering the ,_ngle or incidence to 2 mr.The APS experiments will more typically be located at 40 m from the ring with a
- mirror at. 20 m. The hand-drawn sketch indicates schematically (in a two dimensional_- representat.ion) how the mirrors operate. Imagine th, ellipse rotated a few degrees
each way about its long axis to produce sections of cylindrical and ellipsoidal surfaces.2 Reducing the incidence angle and increasing the distance between the foci amounts to- stretching t,he whole ellipsoid and shrinking its minor radius. A 1'1 ,lirror of about
the 'ame length at 20 m from the ring with a 2 mr angle of incidence would accept'3 ionly about , mr of horizontal radiation, instead of the 4 mr accepted on X.,6(,.
207
/ i ¸............. .....
NSLS X-26C 1:1Focussing Mirror ) , qllj
Fig, (3shows an anamorphic drawing (transverse dimension greatly expanded) of the X26(',
beam line. The horizontal focussing action of the 1:1 mirror is indicat.ed in the planview (upper) and the vertical deflection is illustrated in the elevation view (lower).
Figs. 7-9 illustrate the measured performance of the 1'1 cylindrical x-ray mirror on X26C. ASi(Li) x-ray detector was positioned at a forward scattering angle of 45° to measurephotons scattered through air after passage through a 20 x 20 #m pinhole,
Fig. 7 (upper) shows the measured x-ray energy spectra for both unfocussed and focussedradiation with the pinhole positioned for maximum intensity. Fig. 7 (lower) displaysthe ratio of these two spectra. Note that an enhancement of two-orders of magnitudeis realized over a wide range of photon energies and for the characteristic Ar K x-rayproduction produced from argon in the air. The dip ai. about 5 keV is artificial. Dueto the low x-ray scattering cross sections near this photon energy there are 'very fewcount,s in the scattered-radiation spectra.
209
Fig. 8 is a two:dimensional line plot of the photon flux dist.ribution produced at the focalpoint, with the 1'1 mirror. Note that the focal spot. is nearly round. The unfocussedhorizontal image would have been about 8 cm wide. The full-width-_t-half-nlaximunlor 2ct of the focussed image was about 0.7 mm. Although the mirror specificationcalled for no vertical focussing the verticM beam profile had a 2ct of 0.6 mm, while theunfocussed, was 1.8 mm. This factor of three reduction in vertical height is believedto result from slight, concave curvature down the long axis of the mirror,
210
Focussed beam. profile (horizontal)10.0 ---.- _ .... I - , i .... ,,I I -- I I I
8,0
'_ 6.0
,_",,W
,I,.0Z8h
2,0
0.0 , I I j I , I pkxx_"_::::_
5t 50.a 50.8 50.4 50.2 _0 _.8 49.6 ,9.4 _.2
Horizontal position (mm)
_o Focussed beam profile (vertical.)tO.O - _ l r i i_" I I' I I
V
c_ 8.0 -¢,)
,,,,w,,p
6.0
4,0--
2.0=
_
0.0 I "_._ L_..f-__
82 8.t,B 8t.6 Bf,4 8t,e at 80,8 80,6 BO,480.2 80
Vertical position (mm)
- Fig. 9 shows the horizontal and vertical beam profiles at maximum intensity, The vertical
" profile is asymmetric only because it was clipped on one side by by an aperture in thebe,_m line.
211
Fig, 10 shows the calculated photon-energy spectra for the un(lulat.or A of the APS comparedto those for a typical bending magnet beam line (X26) and a super-conducting wigglerat maximum field strength of ,5 Tesla (XI7), The X17 spectrum (at 4.9 Tesla) is alsotypical of a generic bending magnet at the APS, although, flux at the APS may beso,newhat higher due to the lower source emittance. At, a field strength of 1,1 Tesla,X17 produces essentially the same spect, rum as an NSLS bending magnet port (e,g,x26). Clearly, an undulator provides much higher photon flux at soft. x-ray energiesthan bending magnets or even super-conducting wiggters at the NSLS.
21.2
Scatteredspectra from Si02glassat X-1710' ......- ' I ' I ' 1 ' i • i '
.
" ____,,_ iI PbK fluorescence103
lo'
_ 0 20 40 60 80 100 120
, X-ray Energy(keV)
Ratioof high/low field flux on superconductingwiggler; 10' - , r--,--r---,-----r----__=
J "
_=lO'
_ lO'
o
- lo'"8.oa: 10'
10o , .,,,'1" L J .., 1 , . I , 1 _ J . _ ; ,
0 10 20 30 40 50 60 70 80
X-ray Energy(keV)
. Fig. II is similar to Fig. 7, but here a measurement is made of unfocussed x-ray scattering- front o, glass target on XI7 at 1.t and 4.9 Tesla with only 2 ma of stored electron
beam. The upper spectrum shows the t,wo radiation patterns and the lower comparesthe measured and predicted ratios. The energy dependence of the ratios agree well.The discrepancy in magnitude is attributed to either the loss of some beam when themagnet was ramped down from 4.9 to 1.1 Tesla or a normalization problem with thebeam monitors at such low stored beam currents. Note that this direct comparison of
- the two radiation patterns under otherwise similar conditions indicates that an APS_: bending m_gnet beam line is clearly superior to a comparable NSLS line only at hard- x-ray energies above a few keV.
213
flit
,, . ,_
10"pE"T"TTTTI-III. I ,,,,,m , ,'_ 10mm w
[,,
10-_ -, 10•
, ,,,WIGGLER - O
10._ ' 10_.o #,,
-O ,. % -I,,,,.,."% ti :
CD -20 _ % 13 E_. 10 , 10 •% O0
E X-260 Z
b 10.2,_ BENDING (_t 10_MAGNET ' _ "=
Z10_ 10"
Be WINDOW
ABSORPTION
10-23 10_° _10' 102 103 104 105
E(eV)
Fig. 12 shows the photon flux distributions for a t,ypicaI NSLS bending,m_gnet (X26(Land wiggler (X2,Sj, and the filtering effect of a Be window which absorbs low-ener,
l)hotons. Note lhat the _qux is plotted for photons in _ 1 eV energy bandwidl-rather than the more customary 0,1% wavelength bandwidt, h, Also indicated are t,;_
photoabsorption cross sections for the M-, L-, and K-shells of argon, Note that bro_t/
b,_nd radiation from either the bending magnet or wiggler span the entire rangebincling energies for. ali elect.rons in argon. £he same would be true at the APS 1_even the heaviesi, atoms,
214
PHOBIS:PHOtonBeamIon Sourcei e
' electrL_ I III II I
'; ions extracted_I |Q
,' from trap 'f'II IQ
e ;.A
_J_ t1_ "_, will '
M III1_ _ II "'I1.. ".. Ib
O.IROMATOR "",:,',::
, 7 "'_'--.. ..:'"_ / I / -°*,. "°_. _.4,',*
! SPECTR. / _ "'...,[':;."_ MIRROR
Adapted from K. W. Jones, B. M. Johnson, and M. MeronPhys. Lett. 97A, 377 (1983).
Fig. 13 illustrates the PHOBIS concept,, which was proposed many years ago, The basicidea is to use an ion trap t.o hold ions in the path of broad-band synchrotron radi-at,ion to successively photoionize ions to higher and higher charge states. The first,experimental demonstration of successive inner-shell photoionizat, ion in a Penning iontrap was recently achieved in a collaborative effort on NSLS beam line X26C. See the
contribution t,o these proceedings by David A. Church.
= 215_
NAPFNationalAtomic Physics Facilty
NAPF
A CooledHeavy IonStorageRing
._.oposedto be builtat the
T National Synchrotron Ught Source NA SD LL to be injected with ions from the S
TandemAccel-DecelLaboratory
at BrookhavenNationalLa
CHISR
Fig. 14 inl.roduces the basic elements of NAPF. the proposed National Atomic PhysicsFacility. Such a facility would be ideal for studies of the inner-shell photoionization, ofions with hard x. ravs, as well as a host of other ion-photon, ion-electron, and ion-atominvestigations.
216
ATOMIC PHYSICS FOR THE 90's AND BEYOND
FUb DAMENTAL INTERACTIONS
, THREE-BODY CO_ COULOMB PROBLEM
. QED EFFECTS AT HIGH-Z
• STRONGLY PERTURBING INTERACTIONS
• MANY.BODY [NTERACIqONS/CO R.REI-ATION
. ATOMS IN VERY HIGH FIEI/9S
• TIME REVERSAL & PARITY NON-CONSERVATION IN ATOMS
Fig. 15 summarizes the scientific justification for NAPF. See also the the document, s listedin the bibliography and the contribution to these proceedings by Steve Manson.
217
Fig. 16 indicates the proposed local, ion of-a heavy-ion transfer line from the BNL t,andem
facility to t,he NSLS. The existing transfer line tc) the BNL Alternating Oradient,Synchrol, ron AGS is also shown.
218
CHISR:COOLEDHEAVYIONSTORAGERING
Fig. 17 gives a schematic diagiam of the photon beam from the NSLS x-ray ring interactingwith stored heavy ions.
219
=
" ,, I, ..... III 'I!
BeamLineX-13at the NSLS
COOLED MAIN SIDE APERTURES FRONTHEAVY ION BEAM PORT AND I_O
STORAGERING ,EI'ATIO#; STATION SHUTTERS ------)
'3 Hutch B2 Hutch B1Hutch C Hutch Aux, Hutch Tunnel
% "., .
, ;.,
..... :.. _ • ._- % ..... .--.._ _ '
/ I v..,
/ _-_oto_.Shu,,_'--TailPieceExtension,
Fig. 18 shows some det_dls of the design of a specific superconducting-wiggler beam linel)rOl.,_sed for port X13 at. the NSLS, Note the provision for independent experimenl, t,on the photon beam line during time periods when the heavy-ion storage ring wouldnot be available for SR experiments.
220
=
Fig, 19 illustr,'xtes the wide range of mea,surenlents that would be possible in studying ion-photon, ion-electron, and ion-ion interactions ai, NAPF,
3
"2_
221
PHOTON-ION LUMINOSITY
PHOTON BEAM INTERACI'ING WITH STORED HEAVY IONS:
Imrad ._.._ _
PHOTONS " "
o.o2mrada = 1.2cm b = 6cre "'"-_-_
•, O, 60m A = axb [IONS
NHIN PL - fA enc
Np rene = 1 x 1014 photons/sec-mrad
BANDWIDTH OF 0.1%
b
DEBUNCHED: NI.II = NTOT2,R
b
BUNCHED, 1 > b: NI.II = NTO T Ml
BUNCHED, 1 < b: NHI = NUMBER OF IONS IN ONE BUNCH
Fig, 20 describes the figure of merit for a crossed photon - heavy ion beam experiment-namely, t,he photon - ion luminosity, Tile parameter fenc is the frequency of encounter,which is typically 1 M Hz or 108 passes per second of the stored heavy ions,
222
ConsiderK-shellPhotoionizationof Cu _+
Assume photon energy resolution&E/E of 0.1%(better than 8 eV)and photon flux of 10_ Hz.
m,i w Ni ua ow ml NI lm un on al | m lul iI | | ali qln um alu Q_nnlu | | | | | w m
SIGNAL (K-shellphotoionizationevents)
Cross Section 3.0 x 10-20cm2(near K-edge)
Luminosity 4.3 x 1020cm"2s"_(Ion-photon interactions)
Fig. 21 begins _. cMcul_t, ion of expected signal to noise ratios for a_ specific photoionization
measurement in CHISR at NAPF (to be continued in the next fi,_ure),
223
K'shell Photoionizationof Cu _+ (Continued)
Synchrotron Radiationis PULSED.NSLSx-ray ring normally operated with 25 bunches.w ,,_.,,a,,,d,,w,.,.a ,..ii,_,w _,m,_ ..,,,.J,m _,m,w mm _. In _ _ w _. w _ w _ w _ _ w m w | m m | m w | I m m m m m | n n I m w n w m I
Bunch Width (4(7) 0.6- 1ns
RevolutionFrequency 567.7ns
Duty Factor 01026 - 0.044
TypicalDuty Factor 0.03ali
SIGNAL/BACKGROUNDratio 13/(4000 x 0,03)= 11%m m0m Imnlm m m m _ m mm m m Ima, mumm, ml0mm m m mm _mm _m_m_ _mu_m_ n_ n _ m_mmum mm
Similarcalculationsfor outer-shell ionizationof Cu ionsyield SIGNAL/BACKGROUNDratios of 3 to 9%.
Fig. 22 the continuation of the calculation begun in the preceding figure. Note thai. theconclusion would be ew, n more valid for a similar proposal at the APS, Instead ofa long and costly transfer line from ATLAS, an ECR ion source and linac near the
('HISR could be used for injection.
224
loe '1 1 I I
106" C 8 - _ _._/Au
104 CH6,_R -
2 1°s ......... -- -aL
102- . -
t01 -ECR
N
_0e - Aw -!
'r i•i0" I , i ,, , ,,0 10 20 80 40 50
£)
Fig, 23 compares effective beam currents for a Cooled Iteavy-Ion Storage Ring versus anElecl, ron-Cyclot, ron Resonance Ion Source. ,The overall magnitudes are very dependent
- on specific assumptions about the performance of each type of ion source, but the trendversus increasing charge state is generic. ECR sources are compet.i(,ive at. low chargest,at,es and for light, to medium Z element, s, but CHISR clearly wins as the charge staleand mass of the ion is increased.
225
I a
110keV10-21 I I I I
0 20 40 60 80ATOMICNUMBERZ
Fig. 2,1 gives plots of I._hol.oionization cross sections versus Z for K-, L-, and M-shells of alielements. Note that t,he elements ancl shells covered by different ranges of soft andhard x rays are indicated with dashed lines. While inner-shell studies over a widerange of low to medium Z ions can be performed with soft x rays, such experimentson heavier atoms require the much harder x rays available in abundance at the APSor on a superconducting wiggler at. the NSLS.
226
Spectral Characteristics of Insertion Device Sources
at the Ad:,_._:_:_ Photon Source
P. James ViccaroAdvanced Photon Source
Argonne National Laboratory9700 S. Cass Avenue
Argonne, Illinois 60439
INTRODUCTION
The 7-GEV Advanced Photon Source (APS) synchrotron facility atArgonne National Laboratory will be a powerful source of hard x-rays with
energies above 1 keV. In addition to the availability of bending magnetradiation, the storage ring will have 35 straight sections for insertion device(ID) x-ray sources. The unique spectral properties and flexibility of thesedevices open new possibilities for scientific research in essentially every
area of science and technology. Existing and new techniques utilizing thefull potential of these sources, such as the enhanced coherence, uniquepolarization properties, and high spectral brilliance, will permitexperiments not possible with existing sources.
In the following presentation, the spectral properties of ID sources arebriefly reviewed. A summary of the specific properties of sources plannedfor the APS storage ring is then presented. Recent results for APS
prototype ID sources are discussed, and finally some special x-ray sourcesunder consideration for the APS facility are described.
GENERAL PROPERTIES OF ID SOURCES
Both undulator and wiggler IDs at the APS will be composed of magnetarrays in a planer geometry which set up a spatially oscillating magneticfield along the length of the device [1]. These arrays can either be made upof permanent magnets, with or without high-permeability magnetic poles,or electromagnets. Whatever the structure, the spectral properties of the
devices is related to the peak magnetic field, B0 generated. In particular,
the field results in an oscillating trajectory of the particle beam through thedevice. The amplitude and maximum slope angle depend linearly on both
the field, B0, and the period of the device through the deflection parameter,=
K, defined by:
227
K = 0.933k0B 0 ,
where k0 is the ID magnetic period in cm, and B0 is in tesla. For a K lessthan approximately 10, the maximum Slope angle is given by,
e =K/7,where 7 = 1957 E r is the relativistic factor, and E r is the ring energy in GeV.This is to be compared with the natural opening angle of synchrotronradiation,
which is approximately 73 krad for the 7-GEV APS storage ring.
The spectral properties of a given device will depend on the relative
values of the maximum slope angle, 0, and the opening angle, _t. In the
undulator regime, where K ~ 1, the radiation from each part of thetrajectory is within the radiation opening angle, and interference effectscan occur. This interference causes spatial and frequency bunching which
gives rise to the typical undulator spectrum consisting of narrow bands ofradiation called harmonics. The energy at which these harmonics occur
depends on the ring energy and the peak magnetic field in the device. For asingle radiating particle, the radiative source size and divergence dependon the wavelength of the x-ray and the length of the undulator. Typically,the radiative divergence at the harmonic energy is a fraction of the natural
radiation opening angle, _t, and the photon flux at thisenergy is enhanced.
In the wiggler, where K > 5, the output from the device is a sum ofJ
intensities from each magnetic pole and the spectral output i:; similar to a
bending magnet, but contained within a horizontal angular range of _+K/7.
The spectral output on-axis is approximately N times the output from anequivalent bending magnet source, where N is the number of' magnetic
. poles.
The spatial and angular distribution of the particle beam will affect theundulator spectrum most severely. Since the particles in the beam areindependent, the effective source angular distribution and size .are aconvolution of the radiative and pa-ticle beam distribution parameters,. The
particle beam distributions are approximately Gaussian as is the case forthe central radiation cone at the principal harmonics. For the low-
emittance APS storage ring, the particle beam vertical divergence is on the
order of the Gaussian width (9 urad) of the first harmonic central cone. Inthe horizontal direction, it is a factor of approximately two larger. As a firstapproximation, information concerning the number of photons in a given
bandwidth contained within a given angular aperture can be estimated for
228
the principal harmonics using the convoluted effective source spatial and
angular properties.
The on-axis brilliance BL 0 (sometimes referred to as brightness) isdefined as:
BL 0 = number ofphotons/(0.1%BW mm2mrad 2)
and is equivalent to the total flux at a given photon energy in a fixed
bandwidth (BW) divided by the effective radiative source size and effective
_Jurce divergence in the vertical and hoI_zontal directions.
The on-axis brilliance at the principal harmonics of an undulator
contains information concerning the approximate angular distribution of
the source. In fact, the peak angular flux density of the central radiation
cone is given approximately by the product of BL 0 and the effective source
area. As mentioned, the angular width is the convoluted width of the
particle beam divergence and radiative width.
APS RADIATION SOURCES
Several IDs have been identified as standard x-ray sources for the APS.
These include two planar undulator and two planar wiggler sources.Undulator A, which has the Nd.-Fe-B and vanadium permendur hybrid
geometry, is capable of spanning the photon energy interval fromapprox:imately 5 to 30 keV using first-harmonic radiation. Undulator B,
which also has the hybrid structure, is tunable for approximately 13 to 20
keV. The wigglers A, with the hybrid structure, and B, which has
magnetic structure based on electromagnets, have critical energies of 32.6
and 9.8 keV, respectively. These critical energies are above and below that
for the bending magnet radiation of 19 keV.
In addition, several other devices are described. One of these is an
undulator-wiggler source. This ID for K-values near 1 behaves like an
undulator with a first harmonic in the range of 1 to 2 keV. At closed gap,
and with K - 9, the device is a wiggler with critical energy near 30 keV.
Undulator C is an x-ray source with first harmonic spanning the interval
of 0.5 to 1.5 keV. Both devices are very effective sources spanning the
interval between soft and hard x-ray sources.
The flux through a pin-hole with an angular opening equal to theangular width of the central radiation cone for the first harmonic of
Undulator A is approximately 1013 photons/sec in 0.1% bandwidth at the
229
energy of 8 keV. This value is typical for most undulator sources at the
APS. The total flux within the central radiation cone is approximately 1014photons/sec per 0.01% bandwidth at 8 keV.
APS UNDULATOR PROTOTYPE RESULTS
As part of the R&D effort, the APS has developed two prototype undulator
sources in order to evaluate construction techniques, critical construction
tolerances, and performance. The first of these is a prototype of undulator
A with a period of 3.3cm and a length of approximately 2 m. It was the
first short period undulator to be used as a synchrotron x-ray source. Thedevice was installed on the CESR/Cornell storage ring for a one month
dedicated rxm[2]. The storage ring was modified to have approximately the
same vertical emittance as the APS. The performance of the device was
excellent and satisfied all the requirements for an undulator of this type
installed on the APS. As part of the performance evaluation of the device,
the effect of introducing a taper in the undulator gap was tested. In this
mode, the first harmonic bandwidth increased by a factor of two. At the
same time, the spatial distribution remained essentially unchanged. Thisresult can be explained by the fact that the band width is determined
essentially by the difference in entrance and exit peak fields caused by thetaper in the gap. The spatial distribution at the harmonic, on the other
hand, is determined by the energy of the emitted photon.
A second prototype is the undualtor for the U-5 straight section at the
VUV storage ring at the National Synchrotron Light Source (NSLS). The
device will be used by a multi-institutional mate_als research group in adiverse program. The undulator, which was delivered to the NSLS in
March 1990, will be tested and its performance evaluated in early summer
of 1990. The device has a period of 7.5 cm and a length of 2.3 rh. It has the
lowest random field error of any built to date. Some of the essential designparameters can be obtained from [3].
SPECIAL PURPOSE IDs
Part of the R&D effort in this area will be placed on the development of
techniques which utilize x-rays with a variable degree of elliptical
polarization of ID sources in the region of 2 to 100 keV. In the low-energy
part of this spectral region, techniques used for the investigation of elastic
magnetic scattering and polarization processes will be prominent. In _e
high-energy portion of the spectrum, magnetic Comj)ton scattering will beE
230
II_
important.
At present, there is a significant amount of activity concerning the
development of ID sources capable of producing circularly or elliptically
Brilliance ot gending-Hagnet Radiation from Various SynchroLron Sources
m
244
ADVANCED PHOTON SOURCE
UNDULATOR RADIATION
• ENERGY TUNABILITY (nth Harmonic)
2En(keV) = n 0.949E R
X0(1+K2/2)
K = 0.934BoX 0
B0 = Peak Magnetic Field (T)
X0 = Undulator Period (cm)
ER -Storage Ring Energy (GEV)
. ENERGY WIDTH OF HARMONIC n(Zero Emittance)
AE/E = 1/(nN) N = Number of Periods
ADVANCED PHOTON SOURCE
APS Undulator A (,3.1 cm Period)1st Harmonic Tunablity
On-Axis Brilliance of the First-Harmonic Radiation from APSUndulator A at 7 GeV and i00 mA (The first-harmonic peaks at various energies
are obtained at magnet gap settings of (a) 11.2 mm, (b) 13.9 mm, (c) 16.5 mm,(d) 19.7 mm, (e) 24.7 mm, and (f) 30.1 mm. These calculations include thephase-space dimensions of the positron beam.)
247
248
ADVANCED PHOTON SOURCE
Undulator-Wiggler lDPeriod=8 cmDeflection Parameter K = 0.934 BoXo
3. W. Eberhardt, P. Fayet, D. Cox, Z. Fu, A. Kaldor, R. Sherwood, D. Sondericker, Phys.!
" Rev. Left. 64, 781 (!990)_n
4. J. Zhao, P. Mor4ano0 M. Ramanthan, G.K. Shenoy, M. Schulze, Bull. Am. Phys. Soc..35, 605 (1990)
5. L. Cordis, G. Gantef6r, H. Hesslich,A. Ding, Z. Phys. D3,323 (1986)
6. J. Stapelfeidt, J. W6rmer, G. Zimmerer, T. M611er,Z. Phys. DI_, 435 (1989)
7. C. Brechignac, M. 8royer, Pi', Cahuzac, G. Delacretaz, ?. Labastie, J.P. Wolf, L.W6ste Phys. Hey. Lett. 60, 275 (1988)
8. For a review see: M. D. Morse, Chem. Rev. 86, 1049 (1986)
9. K. Rademann, Ber. Bu_senges. Phys. Chem. o9._,653 (1989)
10. J.C. Lyon, B. Peart, J.B. West, K. Dolder, J. Phys. _, 4137 (1986)=
297
=
Atomic Physics with New Synchrotron Radia0on:Report from the Japanese Working Group
Masahiro Kimura
Department of Physics, Osaka University, Japan
The construction of a new photon facility, SPring-8, is beingstarted this year in Harima, Japan, and the first photon beam is to besupplied to users in 1998. As a next generation photon source, thisfacility will rely mainly upon insertion devices like the APS.
The source has two characteristic features. One is that the photon
flux is ve,T powerful. In atomic physics target density is often verydilute, and, in many cases, coincidence measurement is desirable to getmore definite conclusions. Only with the advent of an intense photonsource such studies become tractable and will compensate a thin target
density. Another feature is that it can yield photons as high as onehundred or two hundred keV as seen in Fig. I. The lower part of the
figure shows the absorption edges of ali elements. Since the K-edge ofuranium is about 120 keV, the new source can be used to ionize even theinnermost shell of the heaviest element.
Recently the committee of the new facility has decided to installlong-distance undulators in addition to 6.5-m undulators. These 30-mundulators can yield photons of much higher brilliance, or soft x-rays, ofhigher coherency. They may also be used to develop FEL (free electronlaser) in soft x-ray region in the future. Therefore our proposals includethe studies which require not only hard x-rays but also soft x-rays.
In order to discuss the possible projects in the field of atomic
physics with these new photon sources, a group was organized inDecember 1988. Members of the group are listed in Table 1. The groupconsists of about 30 Japanese atomic physicists who have intere_ '' in theresearches with this new facility. Two third of them have expe_t.nceusing existing SR sources.
The following themes have been discussed (multiply charged ion isabbreviated to MCI).
1) Spectroscopy of atoms and molecules.2) Photoionization of ions (inclusive of MCI)3) MCl-trap (spectroscopy of MCI, cold MCI plasma)4) Collisions of very slow MCI5) Electronic and atomic structures of microclusters6) PlasmThe report of the working group was printed last May in Japanese,
and my talk is about its contents.
298
Table 1. Li_t of group n_embers
Y. Achiba, N. Kobayashi, and K. Okuno (Tokyo Metropolitan Univ.)H. Anbe, Y. Awaya, and M. Takami (RIKEN)I. Arakawa, and T. Hirayama (Gakusyuin Univ.)N. Hishinuma (Tokyo Univ.)Y. Itikawa (Inst. of Space and Astronautical Science)Y. Isozumi, and T. Mukoyama (Kyoto Univ.)Y. Itoh (Johsai Univ.)S. Kawatsura (Kyoto Inst. of Technology )M. Kimura (Osaka Univ.)T. Koizumi (Rikkyo Univ.)H. Maezawa, A. Ogata, and A. Yagishita (KEK)T. Mizokawa (Nagaoka College of Technology)S. Ohtani, M. Sakurai, K. Sato, and H. Tawara (National Inst. for
Fusion Science)N. Saito (Electrotechnical Lab., MITI)Y. Saito (Nagoya Univ.)Y. Sato (Tohoku Univ.)M. Terasawa, and T. Sekioka (Himeji Inst. of Technology)J. Yoda (National Res, Lab. of Metrology)
- M. Yoshino (Shibaura Inst. of Technology)
1. Spectroscopic study of atoms and molecules
When atoms or molecules absorb high energy photons, inner shellelectrons are excited or ionized. Inner hole states are generally unstable,and several kinds of ions are finally produced through successive Auger
, decays. Such a process is one of the fundamental processes of interactionbetween high energy photons and matter. In such a study the followinginformation is essential:
1 ) energies of hole states.2) ionization potentials to produce multiply charged ions.
Though binding energies of electrons in atoms and molecules areelementary quantities, it is not always easy to determine the accuratevalues. Particularly those of multiply charged ions wb:,ch are determinedoverwhelmingly from theoretical calculations or empirical laws at the
- present stage. Such examples are shown in Figs. 2 and 3.
299
Regarding inner-hole states, the following topics are considered:
a) absorption spectroscopy -- absolute measurements of photoabsorptionb) photoelectron and Aug_;-electron spectroscopy --energy and angulartkistributions of photo- and Auger electronsc) charge analysis of product photoions and their yieldd) coincidence between ejected particles (electrons, photons, and ions)e) partial cross sections for ionization of inner orbitals as a function ofphoton energies.f) partial cross sections for producing multiply charged ions as a functionof photon energies.g) dissociation after photoexcitation of a specific atomic site in a molecule.h) photoetching and photodesorption from solid surfaces and analysis ofsurface electronic structure.
To give an example, Breinig et al. (1980) measured the spectranear the L-absorption edge of Xe with high resolution and determined the
" hole states of 2s-lnl, 2p-lnl, and binding energies of 2s and 2p electronsas limiting values of these hole states. Such methods can be applied toother atoms or ions.
Another method of study the processes is photoion measurement.Such an example is shown in Fig. 4 which was copied from the work ofNagata et al. (1989).
Not only atoms but ions including multiply charged ions will be thetarget of investigation with the future SR. There exist about 4000 speciesof MCI as shown in Fig. 5. In other words, atomic physics can be extendedto two-dimensional from one-dimensional field, and investigation through
isoelectronic sequences can be performed. Such systematic study becomespossible only when multiply charged ions are made targets.
2. Photoionization of ions
Experimental data of photoionization of ions are very scarce since
a sufficiently high density of target ions is not readily available. In
. particular, no measurements for MCI have been reported so far. Evenemploying both intense SR and ion sources of high density such as ECRIS
will not be enough to measure the processes by using a crossed beam
method. An approach involving collinear interaction of photon- and ion-
beams will have to be applied. This method was employed already by
Dolder's group to measure ionization cross sections of some singly-
, charged ions. In Fig.6 the conceptual experimental setup is shown.
300
The development of high density ion sources and the technique of
beam transport including mergi,ag beam method are essential for this
project. This year we will start research and development of t!,is
technique.
3. Multiply charged ion trap
Ion traps can confine ions of very low-energy in smal! space, and
they are useful tools for making precise spectroscopy of ions. By trapping
singly charged ions a lot of works have already been reported.
In this project MCI are trapped, and sectroscopic investigation of
the MCI and a study on cold plasma composed of MCI are to be
undertaken (Fig. 7). Transition wavelengths among fine or hyperfine
structures of certain MCI get into the accessible region for theconventional lasers. These transitions can also be used for laser cooling of
the trapped _ons.Production of cold MCI is one of the very important factors fox
efficient trapping. For such a purpose, the use of inner-shell
photoionization by X-ray is known to be the best method. The recoil
energies of ions produced by x-ray absorption are compared in Fig. 8
with those produced by heavy ion impact.
For MCI, cross sections of charge transfer with residual gas is
certainly large. We have estimated the lifet;mes of MCI when they are in
the residual gas pressure of 10-11Torr (Fig. 9).
Before storing MCI in an actual trap, we measured, as a test, thecharge distribution of Xe produced through hard x-ray absorption. A
beam of white x-ray from a 5.8 GeV electrons in an accumulator ring in
the National Laboratory for High Energy Physics in Tsukuba was
interacted with Xe gas target. The spectral feature of the photon beam is
shown in Fig. 10. The lower energy side was cut by Be window.
Fig. 11 shows the TOF spectrum observed. The mean cbarge is
estimated as 8.8. This mean charge is compared with the previous
measurements (Fig. 12).
._D.evelopment of a 0he-dimensional ion trapA highly-charged-ion source, EBIS (electron beam ion source) has
been successfully used so far. Constructing a highly charged ion source by
-- replacing an electron beam with an SR beam and by trapping product
ions radially by multipole rf field is proposed. This ion source may be
301
called a one.-dimensional ion trap or photon-beam-ion source, lt can also
be used as a tool for studying photon-ion interactions inside the trap.
4, Collisions of very slow MCI
An MCI has a high internal energy in itself, lt is known that suchhigh potential of MCI manifests its specific character when they areinteracted with a target at as low a velocity as possible.
In our proposal, we prepare low energy MCI-beams of very
narrow energy distribution by crossing supersonic atomic beams with SR
(Fig. 13).
In some cases angular distributions are also investigated.
5. Structure and Electronic States of Microclusters
Though size selection is by far easier for ionic species than forneutral species, neutral clusters are, in almost ali cases, much more
abundantly produced. By using the magnetic interaction between the
field of hexapole magnet and the magnetic moment of clusters, we canmake size selection even for neutral clusters. Methods of XPS or XAFS are
t then applied to analyze those isolated, size-selected clusters (Figs. 14-15).
In our proposal, microclusters are produced by making a pulsed
laser of high power illuminate solid jurfaces. By running through the
inhomogeneous magnetic field, only clusters of certain size can converge
to a given point to be analyzed by XPS or XAFS.
So far is the outli:Je of our report. Our investigation, is focussed
mainly on the processes involving MCI. As R&D, developing the beam
transport and ion trapping techniques of MCI are in progress.
302
SPECTRAL BRILLIANCE
photon energy (keV)
.ol ._ _ lo lOO _ooo...............
I '1020"_ 8 GeV Undulalors(4m)__._,_. 1019 ...... 1 --'--
o"_ 1018 .........................
d |1 7 /
10 - -.... _ L_ "" ""_-,,,,O.,I .,- •
10 1 6 .... .,.--.,_'"'" 8 GeV MPW(2m) %%,,. ,1_
11,-.
E is .........L---""cq .............i, 'T.:_ _ ...............
l)cpartmcl_t of Phgsics, lhliversity of Te_ncsscc, lO_oa'villc, TeT_nesscc37996-1200aT_dOat" Ridge Nolio_al Laboratory, Oal_'Ridge, 7'e._lllessce37,5'31-6,']77
\¥11en an atom is photoionized in an inner sllell, there are two tnecha.nisllls bywhich tlle remaining electron cortege relaxes to fill the vacancy: x-ray emission andradiationless Auger and Coster-Kronig transitions. In tlm former, the inner-shellllole moves to _ less tightly bound orbital wittmut increasing tlle number of atomicvacancies. In Auger processes, however, the energy liberated hs' t;ranslk_r of a. less-tiglltly-bound electron to the inner..shell vacancy is transferred to another electronwhich is ejected into the continuunl. In this case, the charge on the residual lollincreases by one. Through a series of radiative and non-radiative processes, tlleinitial vacancy 1)ul)bles tlp until all vaca,ncies arrive at the outermost shell, l)ue tothe many possible routes by which this may occur, there can be a broad distributiollof residual ion charge states characteristic of the decay of a. single inne>shell x,aca1_cy.
There have been several measurements of ion charge distributions following inner-sl_ell photoionization. Using photons from x-ray tubes to produce K vacancies in ar-gon well above a.bsorption edges, Carlson and l(rause measured'the resultant chargedistributions with. a magnetic a,nalyzer. _ More recently, Tonuma et al have usedtime-of-flight techlliques to measure charge distributions of xenon ions resulting fromsynchrotron-radiation photoioniza.tion of I, t2a electrons. _"The results showed a. clea.rdependence on photon energy and L-subshell ionizal, ion tllresholds.
Both Carlson and Krause and Tormma el, al made comparisons of tlmir mea-surements wltl_ tlm resul!,s of Monte-Carlo simulal, ions of charge distrilmtions. The['ormer autlmrs used published radiative a,nd nonradiative transition prol)abilities and,in addition, included estima,tes of shakeofl" calculated in the sudden limit. The re-cent simulations of Tonuma et al employ more accurate ca,lculations of radiative aa.nd nonra.diative 4 transition probabilities and the sudden-approximation estilnates ofC,arlson and Nestor. 5 13oth calculations show general agreement with tlm data.
A number of effects have been omitted froln botll theoretical treatments, llow-ever, .As the atom mltoionizes, outer-shell electrons see a reduced nuclear screening,
- resulting in increa,sed binding energy. As a result, some clla,nnels ma.y become closed.1)ecay rates change as tile supply of oute, r-sllell electrons is depleted. Well abovethe plmtoionization tllreshold, tlm sudden-a.pl)roximation ca.lcula.tions of Ca,rlson andNestor provide a. good description of shakeoff. As the mw.rgy of the photoionizing xray api)roaches tlu'esllold from above, the low-energy photoelectron reina.ins in thevicinity of the atom when the inner-shell hole decays, a,lld in this regime, the two-stepexcita,tion-decay pictllre is not va,lid. The t]lreshold energy dependence of sllakeo[l"tlas been measured by Armen el, a,I6 and was found to rise gradually as the high-energy a.symi)totic limit is approached. Tllese effects ali contribute to _ complicat, edion charge distribution which is strongly photon-energy dependent. The differencesbetween theory and exl)eriment are typically small for low charge st,a.l,es for whichonly a few processes colltribute. The production of very high charge states of, e.g.,xenon, can occur by a large variety of channels and for tllese charge sta,tes theorytypically overestimates their relative l)rol)abilil,y, r
318
17Jeca.use so malz$, processes c_m contribul, e to eat;h cha,rge si,a,te, ii, is difNcult, to de-l,ermiiie l,lle e ffecl, ot' ca.cii by ex;t]nining i;lle l,ol.a.l ion ct!a.rge distribut, ion; \lie. t.ot,a l-ion<.:]large disLribut, ion represelll,s aal a.verage over lna.ny effects. 'I'o overcome this l imit.a.-l,ion, we ha,ve recerll,ly lllea,sured argon-ion product, ion as _ t'uncl, iorl of I)otli plio!;oliCllCTg): and Allger doc.a,yciia.niiol following photoioiiiza.l;ioli of I(-shc'll electrons wit.lihighly rl-lorlocllrorllatic SyllCllrol, rori rltdia, t;ion. When l-nt:h.suro.d 'difli:'reilt.ia.l in tlecaycliamiel, the ion charge disl, ril)i.ltioiis are grea.tly siml)lifie.d. Aria,lysis, iii progress,of l,llcse simplified distribul:ions will l)erlnil, ext,ra.ct,iori o17infol.'ma.t,ion icl:)oilt, i'<;lat,ivc,<lecay rat,cs a.nd slia.keoff eft'ect,s t,}la,l; is obscured in l,he singles sl)ect,r_.
\_:lloli llorl-l-lalizcd 1,oCOll,<.;t,a.lit;l)llol, oli flux, st)rim illl;er(:si, iilg t,lircsllold c,ft't,,.<'l,sca.l-i])c. sc(211iii {,lie c.linrge <list:1"il;_ul,ions Fl?c_q.sur(;(lcoincident witli K-I,.,:_L,>:_ktig(,r (l(_-cla.y. Siiic.e virl, ua.lly a.ll 1;,_:_\,icca.ncies deca,y by L-MM Auger t,r&llSit,iOilS>_:l.rgOllioilssl:lotil_l lit, pro,:l/lced 1)rt.'.doriliril/n{ly in c]lnrgo sl;a.l;e4+. Well a.bove l,]lr('s]loid t,ilereis_ lll n.ddit,iorl, a sul.>st,a.nl,ial COliipolielll, Of Ar '_+ resllll, ing J'rol!i slia,kcoff a,il<l I,-MMMdoul_le-kllger processes, kt, cliergies several hurldrecl e\/ above t,lie I_ pliol,oicJliiza,-
-= (,ioil t.llreshold,, i,lie Ar <_+i.o Ar 4_-r&t,io )l_./.sreached _l,llas.$:i-npl,oi:,ic valine of _ 0.5. alarge colIll)oiJell{ of AI 'a+ is evi(ielll, il.l file eliergy regioil cenl,erecl arolllld l,lle al'gorl"11)l'eSOllit;li('O al:)oul, 3 e\: below Llie K-shell pliot, oiollizat, ion i,hreshold iri l,}ie K-sliellal:>soi'p{ioil specl,rtiin, ']'tlis is dlie Lo c,aplure, of \lie I( electron I;o a.1)olilid 4p orl,,ii.a.l.'J'll_:,ie is a. f_,liggesLioli iii 1,he Ar a+ dal.a ot' capl.ure of t,lle I'( elect,rori 1;obotlnd 51) ail_:l61.)sl,i_l,es also. ,cg'iinilill.'d_d,a,liave 1)eell o}TJl,ained irl, nla.iI.'),ell(!l'giC,.q for l,lle ot,]lor kllgert.ra.lisiLioiis respoiisiiJle for fillilig i,he illit, ia.11( V_'i(_'i-/liCyand exllibit, feA-it,lli't?s similar1,ot,llose stiO\Vli for l.]le Iq-l,,.,aI,u:_(:oirlci(Ieill, dltt.a. '.['tiese. pronouliced sllil'l,s iri clia.rgesl.a.i.ea.re liOl; evldelit, in specl.ra, not ol.)Lidlied ill coiliciderice.
'l._}le expeririie111_required aboul, eiglll, da.y,s.'oi l:l(;i.un Lime, illcluding fOlll' sliifl;s ofl.ii-nilig-illo{le opcrat.iori, and was perforliied ilt l)ect'llll)c'r, 1989, Oil _N_1_]7,_l)ea.rnlirieX-:2-1.,\. ()111' i/.1)l)_lra.i.us COliSiSl,ed of a Lirlie-of-t!iglil, Sl)OCl, l'Olnc, t,e,r tO detect, i-iI'gOli iorisand it. cvliil_lrical rnirror ailalyzer Lo selccl, l)a,rl, icll]ar Auger elccl, roiis. Data. werecollect.e_:i lising {,lie X-o,IA 1_131' COl_lll)Ut,<'r. 'l'tie eXp<'l'illlCIlt W&S l)repared ai, the Oakl/i<lge Nal.io,lal l,_:lborldory iii {it,]:JOl'&f_Ol'it?soccupied iJy l,]le Ulliversi.l,y of '{7'fJiill(:'ss('eaccclerai,or-1)asod a.loinic plib'sics groi.ll:>arid l,ra.llsporl, e(1 {o NSLS. ()lJl' gas-l)llase ex-t)el'iilielil: was isolated fi'oill ring \'aciiiliil })y a. })ervliiillli wiridow.
\Vr, l)rOlJOSeIo (:Olllillll(7 o×l)(;'rilllt:lllS very siilliiar 1,o l,]la.l, disci.lsse(] alJovt: tiSillggasool.is XfiJlOII. 'l'lie <.'xporil_leliia.l al)i)al'a.f011s will remain virl;ually iliit'llari_(.;(l. Iiisul:,seqlielil; e×i)oriiiit'rll, s>wo liope to provide diff'ert.'.litial I)l.illll)ing 1o perliiit, reirio\'alof lile })ery]]illlll v:iil(]o,,v arid access t,o l)]lOlOli c'llorgic,s lower l.}i;l{ {lie 3 keV wilidowcii\off. Tlli.s will l)erinil exl.ensioli of t.iiese exlloi'imeiil.s to the I, edge ot' l<r,)'l)lOli aridllie ]'_ edges of ll(,C)ll and ht:liulrl.
1. ;['. ek. (.',_lllsoll aiid Sl. O. Nrause, Pliys. Rev. 1:77, A16,55, 196,5.2. '1'. 'l))llunia, .ai. Yagisliita, II. Silil)al, a, "1'. l(oizumi, T. l_Ialsuo, K. ,_liillia, '1'.Mi.il,:ovan-ia, arid II. '].'awara, ,J. Ptlys. B: At. Xlol. l']lys. 20, 1,3]-L3(i, 1987.
--- :7..J. il. S<'ofit_]<.l,Al. l)ala iN'lit'I. ])al.a 'Pables 14, 121, 1974.•I. _kl. I|. Clten, B. (7'raso_nanrl, and II. _lai'k, Al,. 1)a(.a Nticl Da(a, '1?able.s 24, J21,1979.
5. T. A. Carlsoii alid C. \V. Nestor, Jr., Phys. Rev. A 8, 2887, 1973.
6. G, B. Arlnen, T. _{berg, K, R.. Karim, J. C. Levin, B. Cra.semann, G. S. Browli,M. H. C.hen, and G. E. Ice, Phys. Rev. Let\. <_4,182, 1985.7. ']". Mukoyan_a, ,Journal of (he Physical Society of Japan, Vol..55, No. 9, 3054,198(;.
=
319
AR,GON-ION CHARGE DISTRIBUTIONS
FOLLOWING,
NEAR- THRESHOLD PHOTOIONIZATION,
JON LEVIN
UT / ORNL
320
MOTIVATIONS,
B. CRASEMANN : INNER - SHELL THRESHOLDPHENOMENA
S. MANSON : EDGES V/ELL KNOWN GLOBALLY,NOT LOCALLY
G. WENDIN : AUGER PROCESSES,RELAXATION,SHAKE-UP FROM INNER HOLES
Decompositionof Ar3+ coincidentwithK-L23L23augerdecayintocomponentsdueto excitationof K electron
intoboundnp levels,
=
347
RR@ON 5+14+ RRTIO
50%_
0.40
K-L23L23 coincidence
0.30-+ Ratio of Ar5+IAr4+ -
+LC)
0.20-
12%--_O.IO -
K ionizationthreshold
0.00 I_ I I I I I-I 0 l Z 3 4 5 6
PH_TCNE3_ERGYRELRTIYETO 4P [xl02]
Ar5+/Ar4+ r@tio depends strongly on In_
348'
WITH HARDER X-RAYS (APS?)
1) Do coincidence with less probable Auger lines(e.g.,K- L1 El).
2) Operate Auger-electron channel at high resolution.
3) Triple coincidence with photon, Auger electron, andphotoion.
4) Do spectroscopy of secondary, tertiary, Augerelectrons to study relaxation.
=
349--
Nuclear Bragg Diffractionof
Synchrotron X-Rays
' SSRL,,John Arthur
Dennis BrownGeorge BrownBill Lavender
Stan RubyL
APS,Ercan Alp
Gopal Shenoy
Allied-SignalDevlin Gualtieri
350
i
Nuclear Bragg Diffraction of Synchrotron X RaysL
In the last few years several groups have successfully carriedout experiments involving the excitation of nuclear resonances usingsynchrotron radiation. Ali the experiments so far have used 57Fe asthe resonant nucleus. The extremely narrow width of the 14.4 keVresonance in 57Fe makes these experiments very difficult at even thehighest-brightness synchrotron beam lines currently available, somuch effort Is being devoted toward improvements in equipment andtechniques. The general aim of this work is to use resonantscattering to produce high-flux beams of extremely monochromaticradiation, which can then be used as source beams for a variety ofexperiments.
This talk, however, will stress the kinds of physics questionsthat can be answered using broad-band sychrotron radiation toinduce resonant nuclear diffraction in perfect crystal samples.Experiments of this type are being carried out today, albeit withdifficulty, using present synchrotron sources. They will becometechnically easy when advanced sources such as the APS becomeavailable, and it is expected that nuclear Bragg diffraction willbecome a standard technique.
- 351--
A!
, next level 122 000 eVI_
3/2 _--
1/2.....~ 10.7 eV Firstexcitedstate
-1/2
-_2 , " i1• I
I
1i- " 14 412.5eV
|
] '!
-1/2 ii10.7 eV Groundstate
1/2
57Fe nuclear excitations
352
Current areas of development
I. Resonant filters for producing intense, highly-monochromaticbeams
_Using crystal and multilayer diffractionTischler, ORNL (NSLS, CHESS)Kikuta, Tokyo (AR-KEK)
II. Physics of resonant diffraction from perfect crystals
Gerdau, Hamburg (DESY)_ van BQrck,Munich_- Smirnov, Moscow
Siddons, BNL (CHESS, HSLS)_ Hastings, BNL
Brown, SSRL (PEP)Arthur, SSRLRuby, SSRL
= 353J
_
_
Applications of resonant diffraction from crystals
I. Materials science probe
Very accurate measurements of hyperfine fields in magneticcrystals
II. Showcase for quantum interference phenomena
Interference between resonance levelsControl of quantization axis, polarizationInterference between states with identical energy eigenvalues
III. Crystallography in a new dimension --interference effects onenergy and time dependence
SpeedupDeviation-angle-dependent energy shifts
354
PEP as a source for resonant nuclear diffractionexperiments
A number of factors combine to make the PEP storage ring atSSRL the premier source for experiments requiring extremebrightness at 14 keV. The high electron energy and large ringdiameter make the electron beam emittance small. The 26-periodpermanent-magnet undulators at beam lines 1B and 5B have kparameters close to unity when the first harmonic is adjusted to14.4 keV. The X-ray beam produced by one of these undulators has adivergence which is only slightly greater than the angularacceptance of a typical diffracting perfect crystal.
355
=
• _.I /
PEP Characteristics
Ring circumference 2200 m
Electron energy 13.5 GeV
Source size 2 mm x 0.2 mm
Electron divergence 50 x 40 14rad
Insertion device 26 period undulator
Photon emmis$iQn .7.5 LLrad,.divergence
(SPEAR 170 urad)
Source - sample distance 56 m
Typical beam spot size 2 x 0.5 mm
Flux @ 14.4 keV 1012 S-1
570o PEP undulator
Flux into 0.01 sr(photons.sec-1. 106 104
10-8eV BW)
Brightness(photons.sec-1. 103 106
mm-2.mrad'2.10-8eV BW)
358
Resonant Nuclear Diffraction Geometry
YIG(002) Si (111)monochromai:orScintillator
Electronics
359
I
YIG
Yttrium iron garnet has a rather complicated crystal unit ceThe (002) reflection is forbidden for scattering from atomicelectrons, lt is also forbidden for nuclear scattering from most ofthe Fe nuclei. However, two groups of Fe nuclei, which haveopposing phases for scattering, can be distinguished from each otherbecause they see local electric field gradients which point indifferent directions. By aligning the internal magnetic field parallelto the EFG of one group and perpendicular to that of the other, theelectric quadrupole shifts of the nuclear resonance energies for thegroups will differ slightly. Thus the scattering from these Fe nucleidoes not cancel exactly. The scattered amplitudes are initially outof phase, and cancel at t=0. However, as time passes the slightdifference in energy brings the two groups into phase and thescattered intensity rises. The period of this "slow beat" is about130 ns.
360
YIG Crystal, structure
cubic unit cell, a = 12.386 A
24 yttrium atoms
96 oxygen atoms
40 iron atoms in several inequivalent sites
(a sites) 16 Fe atoms surrounded by oxygen ,,
octahedra
4 groups of 4, with EFG along (111)directions
(d sites) 24 Fe atoms surrounded by oxygentetrahedra
3 groups of 8, with EFG along (100)directions
1
-- TN = 550 K, (a) and (d) sites ferromagnetic but opposed toeach other
Time distribution of the diffracted intensity from the YIG(0 0 10)
crystal planes. This reflection has the same symmetry as the (002)reflection. At room temperature the internal magnetic field is notsaturated, it increases as the temperature is reduced. Highlyaccurate determination of the hyperfine fields is possible. Note thatthe information is distributed evenly throughout the data, and thatthe background is negligible.
364
1000 --,---_ .-, • ; , , .... v , ' , ,
800 - magnet_ field parallel _
'-'=E : _ to scattering plane
o 600 _r-_ iE= 400- ,O
° ;200
O_ :
0 50 100 150 200 250
Time (ns)
1200---, , , , , _ . _ , ....... , ......i
magnetic field perpendicular N
E
'_ 800 - . to scattering plane0 ¢ .;
o 400 - ; _ t _o -it li ,
0 ' ' ',. I .... J T ,-,',_",_,.,,___-=-_-- .... 1
0 50 100 150 2.00 250
Time (ns)
Changing the direction of the magnetic field in the sample relativeto the photon polarization direction changes the polarizationselection rules for the different hyperfine levels, and therefore
changes the nature of the interference pattern. The beat pattern in(b) is dominated by interference between two levels which inconfiguration (a) have differing polarization and therefore do notinterfere.
36.5
2000 "-'_ ' ' 'r ' _ ' ', ....., '
YIG (002),@
1500 ii _
E0
"---_1000 .- _t!:_ _ ."/'_l "'"",
° ii'5O0 ' ,,"
//
_ J J I , I I J I .! .| ..... "''T'_- "0 50 1O0 150 200 250
Time (ns)
A prominent effect of constructive interference on the energy andtime aspects of the resonant scattering process is the speedupphenomenon. The multitude of coherently-excited nuclei in thecrystal, scattering in phase at the Bragg angle, radiate power morerapidly than a similar collection excited incoherently. There is acomplementary increase in the bandwidth of the resonance. Thegreen curve was calculated using the standard 98 ns half-life forthe 57Fe excitation. The calculation neglects the fast beats due to
. the magnetic splitting of the hyperfine levels, but includes the slowbeat due to the quadrupole splitting. The data (and the dynamicaldiffraction calculation) show a much faster decay.
366
Deviation-angle-dependent energy shifts
The analysis of diffraction from a perfect crystal must includedynamical, or multiple-scattering effects. One of these effects is aslight shift in the effective resonance energy for the collection ofnuclei in the crystal, which varies with the deviation of the incidentradiation from th; Bragg angle. A deviation angle introduces slight,phase errors into the scattering process. For waves which aremultiply-scattered, these errors accumulate. In resonantdiffraction, waves which are multiply-scattered tend to leave thecrystal later in time than those that are scatterd fewer times. Thusthere is a correlation between arrival time at the detector and phaseerror introduced by the deviation angle. A phase shift that isproportional to time is a frequency shift.
The angle-dependent energy shifts are very small. They are,_ visible in the YIG data due to the particular details of the YIG(002)
diffraction condition. When the internal magnetic field is alignednearly parallel to the .incident radiation, some of the hyperfinetransitions are excited only by left-circular light while others areexcited only by right-circular light. The sychrotron beam is linearlypolarized, giving equal amounts of LHC and RHC light. Thus thediffracted time distribution consists of a beat pattern due to LHC
• light lying on top of a beat pattern due to RHC light. The angle-dependent shifts affect ali of the hyperfine levels, in a manner suchthat a shift which causes the LHC beat period to decrease will causethe RHC beat period to increase, and vice versa. A change in the
: deviation angle causes the LHC and RHO beat patterns to shiftrelative to each other. (The quadrupole interaction also shifts theRHC and LHC patterns with respect to each other, but this effect isindependent of deviation angle.) Even though the angle-dependentshifts are very small, it is easy to observe the shift of the RHC beatpattern relative to the LHC beat pattern.
trum of Inelasticakly Scattered Photons in Coincidence with I(-Fluoresconce as a Function
of Scattered Photon Energy at. a Fixed Scattering Angle (90°). Copper target. S('att(_ring
rate is the triple differential scattering cross section (see text.) in units of 10 -'t b/(keV-sr'-').
E,,, is the incident energy.
387
Rate -:
. iJL_r-_ I .0 _z ------- i " "
s- _ T E{,_ /!
]
0
50 40 50 60 70
(k V)
Fig. 11' Inelastic Scattering Spectrum in Cohlcidence with Ii-Fluorescence at Different
hlcident E lergies. Ordinate as iii Fig. 10. 4- 40 % M)sohite scale uncertainty.
388
Adapted from Phys. Rev. A _,, 647 (1989)
Rate
6
/_
I
0 .-_[ i--_-.... +---- -- K! I t T" J" '
i i ' ' ' +5 ' _ 0_ '7.5 8.0 8. 9.0 9.5 I .0Energy (keV)
Fig. 12: Detecting Photon Decay Spectra (Fluorescence)in Coincidence with Inelastic
Scattering (points) and without Coincidence (line).
. 389
Adapted from Phys. Rev. Lett. 59, 1558 (1987)
Rate
il j. T . ! + :, _ ._. _
i >6 (b
5t ,. _ T 'T T i,, ....... :-, I i _. ,i
(c)
+ Tiii_'
t !,13 I t
o-'" ...... • ._'---._-_'_1 T T I
J- 111,,|
_0 +0 50 60 70
E_,, (keV)
Fig 13: 2Ieasured (+ 40 % absohtte scale uncertainty) and Calculated Spectrum of Inelas-
tica_y Scattered Photons in Coincidence with I(-Fluorescence as a Function of Scattering
Angle. Ordinate as in Fig. 10. The scattering angle and corresponding momentum trans-
fer for elastic scattering (q0) times the I(-shell orbital radius (a) are as follows: a) 0 =
118 ° , qoa = 1.11: b) 88 °, 0.90; c) T0°, 0.74; and d) 49 °, 0.53.
390
Adapted from Phys. Rev. Lett. 53, 1606 (1984)
Rate 41 R
,! Co" 2_
. ' '" o /
or-' " .... '" ' ",.-'': ....50 60
qf
; C'
_! Fe! ' "" a
c '.T.'/" \/_\DT.,XE_,, Il! .,.....0 '"' • -. .. .. i
= 4 "56 _
(keV)
Fig. 14: Inelastic Scattering Specu'um in Coincidence with K-Fluorescence measured t)y
Namikawa and Hosoya (Phys. Rev. ietts. 53, 1606 (1984)) for Copper and h'on.
391
Adapted from Phys. Rev. B 4._3.1,1224 (1990)
Rate ,_oo, ' - " 1
:oo_ ,zz_r--li'U_I I_ iz -- , ' I _ __ Iz,_ -zr', i : I _ t , -'
:0 30 48 SO
Zr,
01_ - "r.,.TT_"=" ;" .Z-xz-;":0 30 4O 50
(keV)
Fig. 15' Inelastic Scattering Spectrum in Coincidence with K-Fluorescence _Ieasured
(points) by Manninen, Hamalainen, and Graeffe (Phys. Rev. B41, 1224 (1990)) for
Copper and Zirconium. Incident energy is 59.6 keV.
392
Fig. 16" True (T) and Accideutal (A) Events.
393
Adapted from Rev. Sci. Instrum 59, 407 (1988)
Rate
1000
a)
5OO
50C
Fig. 17: Coincidence Spectra Produced with Both Detectors Sensitive on tile Same CHESS
Pulse (a), Successive CHESS Pulses (b), and the Difference Spectrum (c).
394
Adapted from Rev. Sci. Instrum.5.9.,407 (1988)
Noise / Signal
_,=0
\
\'\
\,
\,\,\
_,=20
0.1 0.2 0.5 1.0 2,0 5,0 10.0
Intensity
Fig. IS' Expected Noise to Signal Ratio as a Function of Beam Intensity versus ), :_--=
Accident,_fl Coincidence Rate / True Coincidence PLate. Curves scaled to agree at, a rcf rcnce
= intensity.
_, 5
Rate
_6ooa,)
6oo- b)
0 _--'_ "_• f ,, I , | ,, , _, , I
0- 20 40 60 80 100
E,_,,,, (keV)
Fi,,;. 19" Sp,,¢:tra Detecte_l by Scattered Phot_n_ Detector without Fluorescence Coin,:i_h:m'e
(Sin_,l,, e.,_ Sp_ctra) with (a) and without (b) T_r;p_t..
396
B,,
_ __\ 11 _L _ -- S
P°
: Fig. 20' Physical Layout of Control Exp(:riment to ._Ieasure Detector Crosstalk. Lines
; with arrows indicate possible path for crosstalk event. B" blocker. T' target, S: shi_!:lcliilg,
SPD' scattered photon detector, and FPD' fluorescence photon detector. See text for
det_dls.
397
Adapted from Rev. Sci. Instrum .__9.,407 (1988)
Rate
IItt I
-60 -
_o ,o _o _o _o _o
E,_.,,,, (keV)t
Fig. 21' Coincidence Spectra from Crosstalk Control Experiment. The scattered photon
detector's view of rh,. target is unblocked for a) and blocke_l _r b).
398
Closing Remarks.
Work_;hop on Atomic Physics at the Advanced Photon Source.
Ivan Sellin, the University of Tennessee, Knoxville, and Physics Division,
Oak Ridge National Laboratory.
Friday, March 30, 1990.
Since it is scarcely possible to cite more than a few, perhaps
unrepresentative examPles of many of the fine results and ideas presentedin the last two days in the I0 minutes I h._ve available, I shall
concentrate instead on extracting elements of basic wisdom we have heard.
Conventional though some of this wisdom may be, we should recall that
wisdom becomes conventional because it is so often right, and therefore
worth heeding.
Brant Johnson recalled that several of the topics we have heard discussed
were already featured in a workshop held on atomic physics at synchrotron
radiation facilities held 1_srly I0 years ago. Photoionization of ions isa leading example, lt is well to remember that the main reason for this is
the still prevailing lack .f availability of facilities for studying such
phenomena, unoerscoring again the persistent, acutely felt needs in our
community for facilities which can assist us in acquiring appropriate
capabilities. There is also an advantage in the delay" it has given
theorists like Steve Manson and G6ran Wendin the ci_ance to study many
detailed examples, to point the way to experimentalists to particularly
important problems that will lead to new insights, and to work out explicit
results which c_n then be compared with new experiments. Thus delay is not
without its utility, so long as it does not outlast the limits of ourinterest.
When new, very large, and therefore nearly unique facilities like the APS,
ESRF, or SPRING come on line, what difficult new conditions for conducting
experiments might w_ face? Speaking as a person whose past experience lies
mainly within the area of accelerator based atomic collisions experiments
pursued at popular heavy ion accelerator facilities, one of the most
difficult tasks is procuri_g enough beam time for experiments. In s_eking
a large enough quantity of beam time per successful applicant, program
advisory committees inevitably ask, "What is ther_ that makes this facilityuniquely useful for your experiment? Why can't this experiment be done at
someone else's facility?"
Uniqueness _guments therefore count for a cry great deal in achieving- good access _o facilities and to beam t_me. lt is thus well to ask, what
is truly unique about a facility like APS?
In a casual conversation I had a year ago with the director _f a large vuv
" ring, I _sked him what he thought a machine like the APS could uniquely do
to advance atomic and molecular physics chat other machines could not
match. Qua iifying his answer by noting that it was likely to be prejudicedby his own long term commitment to probing _alence elec_ron behavior, his
reply came down to this' unless one has to access specifically K shell
electrons of heavy elements to achieve specialized experimental goals, thensince the larger v_,v machines will be able to access the L shells of most
of zhe elemer.cs in the periodic table, there is _ot much to be gained from
higher energy synchrotron radiation facilities for the majority of problemshe would consider "importent".
399
We can of course immmediately agree with Dar____!tof this argument. We heard
from Professor Crasemann about challenges of relativity and qed that are of
course best attacked by studying the most deeply bound levels possible.
From Professors Wendin and Franck, we heard about study of x-ray inelasticand Compton processes for which again hard photons are quintessentiallysuitable.
However, the argument fails to acknowledge a most significant point' the x-
ray intensity is greater at al___lenergies at facilities in the APS class,
not just the hard x-rays for which such rings are optimized. How important
this feature may become is underscored by the many comments speakers have
made concerning how tenuous are 'the gas targets atomic physicists use, andhow near zero are ion densities in ion photoionization experiments. Of
course, not all of this intensity gain will benefit ali experiments, sincethe total flux rather than the brilliance will benefit. But there are
broad classes of important experiments where flux is key, and for those
facilities like APS, ESRF, and SPRING the high flux available will be key
as weil. Some experiments, such as the trapping experiments discussed by
Prof. Church, simultaneously use both soft and hard photons; for such
applications a machine with APS capabilities will be very effective.
Modern progress in atomic and molecular physics has been characterized by
increasingly differential experiments, achieved by use of coincidence
techniques, high en=rgy and angular resolution spectrometric devices, and
position sensitive detection. Several speakers here have emphasized theneed for future coincidence experiments, for example Steve Manson in
pointing out the need for studying the angle and photon en=rgy dependence
of two electron processes above threshold; and Manfred Krause who
additionally commented on the potential value of coincidence techniques in
looking, for example, at various double hole processes. From two other
speakers, Drs. Franck and Levin, we learned about the success already
achieved in adapting coincidence techniques in two quite different
applications.
Such techniques piace an enormous premium on intensity °- the more
dilferential or multiparameter they get, the greater are the intensity
demands. Thus flux that promises to emerge from the APS and like
facilities may make many experiments possible which lower flux facilitiescan never reach.
Fortunately, as x-rays get harder, and inner shell transitions become
increasingly dominated by x-ray decay channels, the intensity demands posed
by multiparameter coincidence experiments are eased by the availability of
efficient, dispersive x-rays detectors such as SiLi and GeLi detectors.While such detectors have the limitations of limited resolution and the
slow pulse rise times which make their use in coincidence experiments
problematic, in many cases the advantages of providing high solid angle a_d
simultaneous energy dispersion are likely to make them valuable tools.
The subject of timing has not been emphasized at this workshop. However,for all of us who contemplate timing experiments, using time of flight
spectrometers, coincidence techniques, or both, it will be important to
have good timing capability. Often this is available ali too rarely, for
most users prefer ali buckets to be filled, not just the single buckets
characteristic of most timing runs at present synchrotron radiation
facilities. I would like to call attention to the pressing need for
development of shutters which can send one burst of light do_ a beam line
400
r
while the ring itself is in standard multibunch operation, shutters wllich
should also provide a synchronous timing signal.
In the time available to me here, I have not been able to summarize the
extensive catalog of future experimental possibilities which various
speakers have presented. Perhaps this effort was not needed, since Dr.
, Kimura's comprehensive account of the highly variegated plans of his
Japnnese colleagues seemed to me to blanket the interests of many of us
ve_ J well. The Japanese study group,s identification of multi-charged ion
structure and collision problems seemed to contain many entries which
perhaps interest many, if not most of us. One such topic mentioned by
Kimura but not covered elsewhere in the workshop is the use of multicharged
ions produced by SR radiation as a source of secondary beams in studyingcollisions of eV energy multicharged ions with atoms and molecules. As
those of you acquainted with ion-atom collisions physics may know, very
promising, similar studies are already underway using MeV beams of highly
charged projectiles as the source of ionizing radiation, in several
laboratories, including our own. It will be very interesting to see howmuch better one may be able to do using SR radiation instead.
The final duty of any workshop summary talk is to express appreciation for
the efforts and achievement of the hard-working organizers in providing astimulating, enjoyable visit here for us all. I would like to close the
workshop by calling for a round of applause in their behall.
- 40 I/_L
PROGRAM
WORKSHOP ON ATOMIC PHYSICS
ATTHE ADVANCED PHOTON SOURCE
March 29-30, 1990
- Argonne National LaboratoryPhysics Building- 203 Auditorium
Argonne, Illinois
403
Thursday, March 29, 1990
8:30 a.m. MOI_ING SESSION I
Chair: Gordon Berry, Physics Division, Argonne National Laboratory,Argonne, Illinois
Welcoming Remarks (10 min)Alan Schriesheim, Director, Argonne National Laboratory,Argonne, Illinoi_
Introduction to the Advanced Photon Source (40 min)David Moncton, Associate- Laboratory Director for theAdvanced Photon Source, Argonne National Laboratory, Argonne,, .
Illinois
Atomic Physics with Hard Synchrotron Radiation: Introduction andOverview (40 rain)
Bernd Crasemann, Chemical Physics Institute, University ofOregon, Eugene, Oregon
X-ray Photoionizstion of ions and Atoms: New Frontiers (40 min)Steve Manson, Department of Physics, Georgia State University,Atlanta, Georgia
10:40 a.m. Coffee Break
11:00 a.m. MORNING SESSION II
Chair' Uwe Becker, Technical Institute of Berlin, West Germany
Photoionization of Excited Atoms and Ions Using Synchrotron Radiation:Present Status and Future Trends (40 min)
Francois J. Wuilleumier, Laboratoire de Spectroscopie Atomique etIonique, et Laboratoire pour l'Utilisation du RayounementElectromagnetique, Universite Paris-Sud, Orsay, France
Atomic Physics at the Advanced Light Source (40 min)Alfred S. Schlachter, Lawrence Berkeley Laboratory, Berkeley,California
12'20 p.m. Lunch in the Argonne Cafeteria, Dining Room C
4o4
Thursday, March 29, 1990
1:20 p.m. AFTERNOON SESSION I
Chair: Yohko Azuma, Physics Division, Argonne National Laboratory, ,/_Argonne, Illinois
The RIKEN-JAERI 8-GEV Synchrotron Radiation Project SPring-8 (40 min)Yohko Azuma, The Institute of Physical and Chemical Research,RIKEN, Japan
Photoionization of Ions andthe General Program in Atomic and MolecularPhysics at Daresbury (40 rain)
John B. West, Daresbury Laboratory, England
Multicharged Ion Research Using the Advanced Photon Source (40 min)David A. Church, Physics Department, Texas A & M University,Texas
d
3:20 p.m. Coffee Break
3:45 p.m. AFTERNOON SESSION H
: Chair: Larry Toburen, Batelle Pacific North-West Laboratories, Richland,Washington
Atomic Physics with Hard X-Rays: Perspectives and Opportunities (40 min)Goran Wendin, Institute of Theoretical Physics, ChalmersUniversity of Technology, Goteborg, Sweden
Thoughts on Future ESSR Studies of Inner Core Levels (40 min)_
Manfred O. Krause, Oak Ridge National Laboratory, Oak Ridge,Tennessee
: Beam Line Considerations for the Experiments with Highly-Charged Ions(40 min)
Brant M. Johnson, Physics Department, Brookhaven NationalLaboratory_ Upton, New York
5:45 p.m. Adjourn
Buses to the Hotel, and then to the banquet (returning to the hotel- about 9 p.m.)
: 6:45 p.m. _ and Banquet_ at Carriage Greens Country Club_
4O5
Friday, March 30, 1990
8:30 a.m. MORNING SESSION i
Chair: Pedro Montana, Advanced Photon Source, Argonne NationalLaboratory, Argonne, Illinois
Applications of High-Brilliance X Rays from Insertion Devices at the APS(40 min)
James P. Viccaro, Advanced Photon Source, Argonne NationalLaboratory, Argonne, Illinois
Can a Powerful Source (APS) Cast Useful Light on Atomic Hole StateProcesses? (40 min)
Paul L. Cowan, National Institute of Standards andTechnology, Gaithersburg, Maryland
Studies of Clusters (30 min)Wolfgang Eberhardt, Exxon Research and Engineering, Annandale,New Jersey
10:20 a.m. Coffee Break
11'00 a.m. MORNING SESSION II
Chair: Indrek Martinson, Lund University, Sweden
Atomic Physics with Hard Synchrotron Radiation: Report from the Japanese"Working Group" (40 min)
Masahiro Kimura, Department of Physics, Osaka University,Osaka, Japan
11:45 a.m. Tour of the Advanced Photon Source model
Buses to building 360, returning to the cafeteria
12:30 a.m. Lunch, Argonne Cafeteria, Dining room C
4o6
i
Friday, March 30, 1990
1'30 a.m. AFI_RNOON SESSION
Chair; Noura Mansour, Physics Division, Argonne National Laboratory,Argonne, Illinois
Argon-Ion Charge Distributions Following Near-Thereshold Photoionization
(30 min) 7_,.Ion C. Levin, Physics Department, University of Tennessee, _Knoxville, and Physics Division, Oak Ridge National Laboratory,Oak Ridge, Tennessee
Resonant Nuclear Scattering with Synchrotron Radiation (40 min)John Arthur, Stanford Synchrotron Radiation Laboratory,Stanford, California
Revealing Inner Shell Dynamics with Inelastic X-RayScattering (30 min)Carl Franck, Department of Physics, Cornell University, Ithaca,New York
3:10 p.m. Closing RemarksIvan Sellin, Physics Department, University of Tennessee, Knoxville,and Physics Division, Oak Ridge National Laboratory, Oak Ridge,Tennessee
=.
3:20 p.m. Adjourn
L
4O7
WORKSHOP PROGRAM AND ORGANIZENG COMMI'ITEE
H. Gordon Berry
Yoshiro Azuma l Argonne Physics DivisionNoura Berrah Mansour
Yohko Awaya, RIKEN, JapanDavid Church, Texas A&M UniversityBernd Crasemann, University of OregonJoseph L. Dehmer, Argonne Biological, Environmental and
Medical Research DiLvision
Keith Jones, Brookhaven National LaboratoryAlfred Schlachter, Lawrence Berkeley LaboratoryIvan A. Sellin, University of TennesseeFrancois Wuilleumier, Universite Paris-Sud
ArgonneNationaJLaboratory TechnicaJUniversityof B_din Optic-ElectronicCorp,._rationBuilding360 Hardenbergstr.36 11545Pagemill9700 South CassAvenue D 1000Bedin12 Dallas,TX 75243
Argonne, IL 60439 WESTGERMANY
IgnacioAivarez MichaelJ. Bedzyk Ronald GeorgeCavetlLaboratodo DeCuemavaca, CHESS Department of Chemistry
InstitutoDe Fisica, Unam CornellHigh Energy SynchrotronSource Universityof AlbertaAl:x:lo,Postal 139-B Cornell University Edmonton,AttaT6G 2G2Cuemavaca, Morelos62191 Wilson Laboratory CANADAMEXICO Ithaca, NY 14853-8001
Argonne NationaJLaboratory Albert-Ludwigs-Universitat/Freiburg Argonne National LaboratoryBuilding 203 Hermann-Herder-Stral_ 3 Building3609700 South CassAvenue D7800 Freiburg 9700 South Cass AvenueArgonne, IL 60439 WESTGERMANY Argonne, IL 60439
RonaJdoS. Barbied MerwvnB. Brodsky DavidA.ChurchChemistry' Department M==terialsSdence Division Physics Department
Incianan University Argonne Nat'JonalLaboratory Texas A&M UniversityBloomington, iN 47405 Building360 College Station, TX 77843
9700 South CassAvenueArgonne, IL 60439
Susan Barr DavidCarnegie PaulCowan
Biotogy Advanced Photon Source Nat1 insL of Sdence & TechnologyArgonne National Laboratory Argonne National Laboratory Gaithersburg, MD 20899
= Building 2C2 Building3609700 South Cass Avenue 9700 So,JthCassAvenue
Argonne, IL 60439 Argonne, _L 60439
4!1
Ben _dCrasemann Patrick O. Egan RuprechtHaenselPhy.,'.icsDepartment L-Division ESRS
Universityof Oregon LawrenceLivermore National Laboratory GrenobleEugene,OR 97403 L-45 FRANCE
P.O.Box 808
Livermore,CA 94550
Joseph L.Dehmer Frank Y. Fradin RobertG. HayesEnvironmental Research Associate LaboratoryDirector Chemistry Department
A,rgonne National Laboratory PhysicaJResear,,;h Universityof Nortre DameBuilding 203--C125 ArgonneNational Laboratory NotreDame, IN 46556_3700South CassAvenue Building221a,rgonne, IL 60439 9700 South CassAvenue
Argonne,IL 60439
_atricia M.Dehmer Cad PeterFranck EdvardHeibergEnvironmental Research Physics Department Physics Department
Argonne National Laboratory Cornell University University of ChicagoBuilding203-B161 ClarkHail 5747 South Ellis Avenue
_-2.700South CassAvenue Ithaca, NY 14853 Chicago, IL 60637Argonne, IL 60439
_im PatrickDinneen Jean W. Gallagher 'RussellH.HuebnerPhysics Standard Reference Data Advanced Photon Source
Argonne National Laboratory National Institute of Standards & Tech. Argonne National LaboratoryBuilding203 Physic" A323 9700 South Cass Avenue9700 South Cass Avenue Gaithersburg, MD 20899 Argonne, IL 60439Argonne, IL 60439
Scott R.Dix DonaldS. Gemmell ErmannoJannitti
Granville-Phi}lips Company Physics Division c.loDip. E]ertronica ed Informa_ca
3800 North Wilke Road Argonne NationaJLaboratory Universita di PadovaArlington, IL 60004 Building203 Via Gradenigo G/A
9700 South Cass Avenue 35131 Padova
Arg,unne, IL 60439 ITALY
Robert Dunford Gordon L Goodman Brant M.Johnson
Physics Division Chem;stry Division Department of Applied Science
Arsonne National Laboratory Argonne National Laboratory Brookhaven National Laborator'/Builcing 293 Building200 Building 8159700 South Cass Avenue 9700 South Cass Avenue Upton,NY 11973Argonne, IL 60439 Argonne, IL 604.39 ,
WoifgangEberhardt JohnGustavsson Keith W. Jones
ExxonResear_--h& Engineering Company Intema_onal Relations Departmentof Applied Science
F,oute 22 East Natural Sciences Research Counse_ Building815AnnandaJe,NJ 08801 P.O Box 6711 Brookhaven National Laboratory
11385 Stockholm Upton, NY 11973SWEDEN
4!2
ElliotKanter Scott D.Kravis DanLegniniPhysics Division Physics Dep_."l_nent Advancad Photon Source
Argonne National Laboratory Texas A&M University Argonne Nal_onalLaborator,!, Building 203 TAMU Building 360
9700 South Cass Avenue CollegeStation, TX 77843 9700 South Cass AvenueArgonne; IL 60439 Argonne, IL 60439
Teng _k Khoo CharlesKurtz Jon C. Le'4n
Physics Division Physics Division University oi Tennessee/ORNLArgonne Nadonal Laboratory Argonne National Laboratory 10016 Cedar Croft CircleBuilding 203-F145 Building203 Knoxville, TN 379329700 South CassAvenue 9700 SouthCass AvenueArgonne, IL 60439 Argonne, IL 60439
• Ali M.Khounsary Mickey D.Kut:zner GuokuiUu
Advanced Photon Source Physics Department Chemistry Division
Argonne National Laboratory Andrews University _rgonne National Laboratory-Building 360 Bemen Spnngs, MI 49104 Building 200, M-1699700 South Cass Avenue 9700 South Cass Avenue•Argonne, IL 60439 Argonne, IL 60439
MasahiroK]mura TuncerM.Kuzay Zhengtian Lu
Department of Physics Advanced Photon Sourc_e Physics Division
_saka University ArgonnJ National Laboratory Argonne National Laboratory1oyonaka, Osaka 560 Building3_0 Building 203
-JAPAN 9700 South Cass Avenue 9700 South Cass AvenueArgonne, IL 60439 Argonne, IL 60439
orn KJippert Victor H.S.Kwcng Steven T.Manson
',dvanced Photon Source Physics Department Physics & Astronomy
.rgonne NatJonatLaboratory University of Nevada. Las Vegas Georgia State University:'ullding 360 4505 Maryland Pa,nkway Atlanta, GA 30303- 700 SouI_ Cass Avenue LasVegas, NV 89154__,rgcnne,IL 60439
ac!av O. Kostroun Jayan_ Labiri ,",louraB.Mansour
_4uc!earSci. and E.qgineeringProg. De#ar'mnentof Physics Physics Division
.,/ard Laboratory Southern College of Technology A,'gonne National La_orator'!omeil Universl_ 2200 South Madetta Parkway -muilding203
_aca, NY 14z353-,'-701 Manet'ta,GA 30060 9700 South Cass AvenueArgonne, IL 604-39
anfred O. Krause _ng LaJ Vincent Jame._,Marchet'ti
'-hemis_'t Department Coatings Department Prog. in Nuc. Science and E_gme,_ring
ak F_id_eNational Laboratory Olmtic-E!ec_'onicCorporation 'Nard Laboratory-.Jil¢ing450_JN 11545Pagemill Cornell UniversityO. Box 2008 Dallas, "IX 75243 Ithaca, NY 14.853_k Fddge,TN 37831--6201
_
413
=__
IndrekMartinson Bengt Johannes Olsson David G. Rognlie
Department of Physics Synchotron Radiation Center/CSRF Blake industries Incorporatied
University of Lund University of Wisconsin-Madison 660 Jerusalem RoadSo!vegatan 14 3731 Schneider Drive, FIoute 4 Scotch Plains, NJ 07076S-22362 Lund Stoughton, Wl 53589--3097
SM/EDEN
Rulon Mayer David John Pegg Alfred S. Schlacnter
Physic'_ Oepartm, ent Department of Physics ALS
U.S. Department of Commerce University of Tennessee Lawrence Berkeley LaboratoryNational Insti,'ute of Standards & Technology Knoxville, TN 37996 MS 46-161
Physics Building, Room A 141 Berkeley, CA 94720Gaithersburg, MD 20899
Dennis Miils Gilbert Jerome Per'low Alan Sc.h,qesheim
Advanced Phuton Source Physics Division Director
Argor:,,e National Laboratory Argonne National Laboratory Office of the Direc*,orBuilding 360 Budding 203 . Argonne National Laboratory9700 South Cass Avenue 9700 South Cass Avenue Building 201
Argonne, IL 60439 Argonne, IL 604.39 9700 South Cass AvenueArgonne, IL 60439
Argonne National Laboratory Baker Maqufacturing Company University of Tennessee,ORNL9700 south Cass Avenue 133 Enterprise Street Building 5.500
Argonne, IL 60439 Evansville, WI 5371 1 P.O. Box 2008Oak Ridge, TN 37830--3377
Pedro Montana Stephen Pra_ Amar']it Sen.Advanced Photon Source Enviror_mental Research Physics and Astronomy Department
A_gonne Nation_ I.._boratory Argonne National Laboratory The University of ToledoBuilding 360 Building 203-C-141 2801 West Bancroft Street9700 South Cas._ Avenue 9700 South Cass Avenue Toledo, OH 43606
Argonne, IL 604.."9 Argonne, IL 604.39
Joseph E. Nordgren Mark Leo Raphaeiian Gopal Shenoy
Departmer_t of Physics Physics Advanced Photon source
Uppsala University Argonne National Lmi::orato ry Argonne National Laccrator'tBox 530 Eulicing 203 Building 360
S--751 21 Uppsala g700 South Cass Avenue 9700 Sou_h Cass Avenue
SWEDEN Argonne, IL 60439 Argonne, IL 8042,9
Shunsu ke Ohtani Bnan Rodricks R_bert SmitherInsatute for Laser ,Science Advanced Photon source Advanced Photon Source
Univ. of E',ec_o-Communications Argonne National Laboratory Argonne National Laboratory
Chofu Tok?o 782 Builcing 360 Budding 360
JAPAN 9700 South Cass Avenue 9700 scutch Cass Avenue
Argonne National Laboratory Lawrence Livermore National Lab. Argonne Nadonal Lat_ratoryBuild!:',g360 L..326 Budding3609700 South Cass Avenue P.O, Box 808 9700 South Cass Avenue
Argonne, IL 60439 Livermore,CA 94.550 Argonne, IL 60439
Donald K.Stevens Goran P.Wendn Bruce J.Zabransky
Office of Basic Energy Sciences Institute of Theoretical Physics Physics Division
,_ Office of Energy Research Chalmers University of Technology Argonne National I_ab_raloryU.S. Department of Energy/DC S-41296 Goteborg 9700 South Cass Avenue
Washington,DC 20545 SWEDEN Arcjonne,IL 60439
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-_ Canadian Synchrotron Radiation Facility Chicago District Office,B 3725 Schneider Drive Cray Research, Inc.
Stougnton, Wl 53589 Suite 6101211 West 22nd StreetOak Brook, IL 60521
Richard N.Thudium DavidW'mn. Analytical Science Physics Department
GoodyearTire & Rubber Company Andrews University142 Goodyear Boulevard Bemen Springs, MI 49104Akron, OH 44305
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