The GlueX Photon Beam Richard Jones, University of Connecticut ueX Photon Beamline-Tagger Review Jan. 23-25, 2005, Newport News presented by GlueX Tagged Beam Working Group University of Glasgow University of Connecticut Catholic University of America
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The GlueX Photon Beam Richard Jones, University of Connecticut GlueX Photon Beamline-Tagger ReviewJan. 23-25, 2005, Newport News presented by GlueX Tagged.
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1. Rates reflect a beam current of 3A which corresponds to 108 /s in the coherent peak, which is the maximum currentthe maximum current foreseen to be used in Hall D. Normal GlueX running is planned to be at a factor of 10 lowera factor of 10 lower intensity, at least during the initial running period.
2. Total hadronic rate is dominated by the nucleon resonance region.
3. For a given electron beam and collimator, background is almostindependent of coherent peak energy, comes mostly from incoherent part.
2,3
1
1
1
15Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
III. Electron Beam Requirements
beam energy and energy spread range of deliverable beam currents beam emittance beam position controls upper limits on beam halo
Specification of what electron beam properties are consistent with this design
16Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Electron Beam Energy
effects of endpoint energy on figure of merit:
rate (8-9 GeV) * p2 @ fixed hadronic rate
The polarization figure of merit for GlueX is very sensitive to the electron beam energy.
Requirement: >12 GeV
Decreasing the upgrade energy by only 500 MeV would have a substantial impact on GlueX.
17Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Electron Beam Energy Resolution
beam energy spread E/E requirement: < 0.01 % r.m.s.0.01 % r.m.s. compares favorably with best estimate: 0.06 %0.06 %
absolute energy scale determination to 0.1% via known meson masses in the GlueX detector: eg. (1020)
p + + - n
1. tied to the energy resolution requirement for the tagger
2. derived from optimizing the missing-mass resolution in the channels with a missing final-state particle.
Typical channel analyzed usingTypical channel analyzed usingthe missing mass technique:the missing mass technique:
18Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
upper bound of 3 3 A A projected for GlueX at high intensity corresponding to 108 /s on the GlueX target.
with safety factor, translates to 5 5 AA for the maximum current to be delivered to the Hall D electron beam dump
during running at a nominal rate of 107 /s : I =I = 300 nA300 nA
lower bound of 100 pA 100 pA is required to permit accurate measurement of the tagging efficiency using a in-beam total absorption countertotal absorption counter during special low-current runs.
similar to low-current operation in Hall B
Range of Required Beam Currents
19Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Electron Beam Emittance
requirement : << 1010-8-8 m m••rr all expressions are r.m.s. values
derivation : virtual spot size: 500 m radiator-collimator: 76 m crystal dimensions: 5 mm
In reality, one dimension (y) is much better than the other (x 2.5)
This is a key issue for achieving the requirements for the GlueX Photon Beam
Optics study: goal is achievable, but close to the limits according to 12 GeV machine models Optics study: goal is achievable, but close to the limits according to 12 GeV machine models
20Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Hall D Optics Conceptual Design Study
energy 12 GeV
r.m.s. energy spread 7 MeV
transverse x emittance 10 mm µr
transverse y emittance 2.5 mm µr
minimum current 100 pA
maximum current 5 µA
x spot size at radiator 1.6 mm
r.m.s.
y spot size at radiator 0.6 mm
r.m.s.
x spot size at collimator 0.5 mm
r.m.s.
y spot size at collimator 0.5 mm
r.m.s.
position stability ±200 µm
Summary of key results:
21Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Must satisfy two criteria:1.1. The virtual electron spot must beThe virtual electron spot must be centered on centered on
the collimator.the collimator.
2.2. A significant fraction of the real electron A significant fraction of the real electron beam must beam must pass through the diamond crystal.pass through the diamond crystal.
criteria for “centering”: x < x < mm
controlled by steering magnets ~100m upstream~100m upstream
Electron Beam Position Controls
1.1. Using upstream BPM’s and a known tune, Using upstream BPM’s and a known tune, operators can “find the collimator”.operators can “find the collimator”.
2.2. Once it is approximately centered ( Once it is approximately centered ( 5 mm ) 5 mm ) an active collimator must provide feedback.an active collimator must provide feedback.
22Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Electron Beam Halo
two important consequences of beam halo:1.1. distortion of the active collimator response matrixdistortion of the active collimator response matrix
2.2. backgrounds in the tagging countersbackgrounds in the tagging counters
Beam halo model: central Gaussian power-law tails
Requirement:
r /
central Gaussianpower-law tailcentral + tail
1 2 3 4 5
Integrated tail current is less than
of the total beam current.1010-5-5
~-4
23Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Photon Beam Position Controls
conventional BPM’s provide coarse centering
position resolution 100100m r.m.s.m r.m.s. a pair separated by 2m : 4mm r.m.s. at the collimator4mm r.m.s. at the collimator matches the collimator aperture: can find the collimator can find the collimator
primary beam collimator is instrumented
provides “active collimation” position sensitivity out to 30mm30mm from beam axis maximum sensitivity of 200200m r.m.s.m r.m.s. within 2mm
24Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Overview of Photon Beam Stabilization
Monitor alignment of both beams BPM’s monitor electron beam position to control the spot on the
radiator and point at the collimator
BPM precision in x is affected by the large beam size along this axis at the radiator
independent monitor of photon spot on the face of the collimator guarantees good alignment
photon monitor also provides a check of the focal properties of the electron beam that are not measured with BPMs.
1.1 mm
3.5 mm
1contour of electron beam at radiator
25Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Active Collimator Design
Tungsten pin-cushion detector
used on SLAC coherent bremsstrahlung beam line since 1970’s
SLAC team developed the technology through several iterations
reference: Miller and Walz, NIM 117 (1974) 33-37
SLAC experiment E-160 (ca. 2002, Bosted et.al.) latest users, built new ones
performance is known
active device
primary collimator (tungsten)
incident photon beam
26Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Active Collimator Simulation
12 cm 5 cm
27Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
12 cmx (mm)
y (m
m)
current asymmetry vs. beam offset
20%
40%
60%
Active Collimator Simulation
28Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Detector response from simulation
inner ring ofpin-cushion plates
outer ring ofpin-cushion plates
beam centered at 0,0
10-4 radiatorIe = 1A
29Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Active Collimator Position Sensitivityusing inner ring only for fine-centering
±200 m of motionof beam centroil onphoton detector
corresponds to
±5% change in theleft/right currentbalance in the innerring
30Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Photon Beam Quality Monitoring
tagger broad-band focal plane counter array necessary for crystal alignment during setup provides a continuous monitor of beam/crystal stability
electron pair spectrometer located downstream of the collimation area sees post-collimated photon beam directly after cleanup 10-3 radiator located upstream of pair spectrometer pairs swept from beamline by spectrometer field and
detected in a coarse-grained hodoscope energy resolution in PS not critical, only left+right timing coincidences with the tagger provide a continuous monitor
of the post-collimator photon beam spectrum.
31Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Other Photon Beam Instrumentation
visual photon beam monitors total absorption counter safety systems
32Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
V. Diamond crystal requirements
how much to say here? should probably be brief
33Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Diamond Crystal Properties
limits on thickness from multiple-scattering rocking curve from X-ray scattering
natural fwhm
34Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006
Diamond crystal: goniometer mount
temperature profile of crystalat full operating intensity
oC
35Richard Jones, GlueX Beamline-Tagger Review, Newport News, Jan 23-25, 2006