Experience with Asymmetric Hadron Collisions at RHIC Todd Satogata (and a cast of thousands) CERN p-A Workshop May 25, 2005 Brief RHIC machine description, program goals Challenges and limiting factors Injection at same rigidity Ramp design and performance Conclusions
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Experience with Asymmetric Hadron Collisions at RHIC Todd Satogata (and a cast of thousands) CERN p-A Workshop May 25, 2005 Brief RHIC machine description,
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Experience with AsymmetricHadron Collisions at RHIC
Experience with AsymmetricHadron Collisions at RHIC
Todd Satogata(and a cast of thousands)
CERN p-A Workshop May 25, 2005
Brief RHIC machine description, program goals Challenges and limiting factors Injection at same rigidity Ramp design and performance Conclusions
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 2/21
The RHIC LayoutThe RHIC Layout
RHIC rings are independent except for DX magnets 4.3T, 180mm aperture “combiner” magnet between two rings Design bend angle is 18.86 mrad Deuteron Z/A=0.5, not far from Au Z/A=0.4 no need to move DX magnets
Blue RingYellow Ring
AGS
MP6
MP7
Tandems
Booster
Linac
RHIC
STAR
PHENIX
PHOBOS BRAHMS
d Au
DX
DXD
0D0
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 3/21
Program Goals and AchievementsProgram Goals and Achievements
16 weeks of setup and operations in FY03 schedule Short time: only one energy, only one ring configuration Decision made with experiments, motivated by early d
setup Deuterons in blue ring only, Gold in yellow ring only
All major program goals met within this running periodPerformance Goal Achieved
Setup/Ramp-up time [days] 14/21 18/20 days
Storage energy [GeV/u] 100 100
Number of bunches 55 110/55
* [m] 2 2/3/4
Diamond length [cm] 20 15
Peak luminosity [x1028 cm-2 s-1] 4.0 6.2
Average luminosity (store) [x1028 cm-2 s-1]
1.6 2.8
Integrated luminosity (week) [nb-1/week]
4.0 4.6
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 4/21
Program Goals, Achievements, ChallengesProgram Goals, Achievements, Challenges
Many challenges for a short run Injector performance and mode switching Ramp design issues
Inject at constant B, then constant frequencyCommon DX magnets, crossing angles, optimal *Separate transition jumps in both rings
110 bunch operations, vacuum and radiation issues Luminosity monitoring (ZDC acceptance) Secondary beams, experiment backgrounds, ion beam IBS Instability monitoring and amelioration
Storage Parameter Au Goal Au Achieved d Goal d Achieved
Intensity/bunch 1.0x109 0.7x109 0.8x1011
1.2x1011
Total intensity (55/110 bunches) 55x109 38/60x109 45x101
1
57/69x1011
Transverse emittance (95%, rad)
10-40 10-30 15 12
Bunch length [ns] 5 5 5 5
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 5/21
Injector ChallengesInjector Challenges
Both Tandems required Foil changes scheduled
routinely No redundancy against failure
Deuteron Z/A=1/2 is very low Longitudinal emittance and
intensity were major challenges Mode switching
All transfer lines (big magnets) Stripping foils moved in/out Kicker PFNs adjusted
(dominated mode switch time) Met 5 minute goal after 4 weeks
Inject d then Au to limit effects of IBS at injection
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 6/21
d beam only about 1/3 rigidity of Au in Booster, extraction septum didn’t regulate so low.
Transferred 2/3 Booster bunches to AGS in 6 cycles; 124 bunch merge in AGS Booster extraction septum AGS injection kicker magnet
pulse length
Increased d KE from Tandem to 8.7 MeV/u, allowing h=2 capture. Proton RF cavities allow merge at 830 kHz to h=1 and eliminated septum pulse length issues. 84 bunch merge in AGS
doubled total intensity
Deuteron Booster bunch merge
RF harmonic h=2 to h=1
Deuteron intensity: 5-6x1010 to 1-1.1x1011
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 7/21
Single-Bunch Run PerformanceSingle-Bunch Run Performance
d merge
Majority of run was single-bunch intensity limited Multiple demands on injectors made optimization difficult Very little lead time for injector preparation before run
startNew species (d) always contain surprises
Au was almost always single-bunch limitedLater resolved to be heavy ion injector septum apertureTandem/source inconsistency apparent late in run
Deuteron bunch merge worked well in last month of run
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 8/21
Total Intensity Run PerformanceTotal Intensity Run Performance
56110
Pushed bunch # since single-bunch intensity was limited Maximum total intensity 60-65x109 Au, near ecloud limit Deuteron max total intensity around 70x1011 d Upgraded injection kickers worked well for 110 bunches Long-range beam-beam present but not disasterous
Locked RF frequencies between rings, no modulation Final performance limited by Au injector, d total intensity
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 9/21
Injection at Same RigidityInjection at Same Rigidity
Blue and Yellow rings independent (except DX) Inject at same rigidity in both rings, different frf
Minimize transfer line changes, maximize flexibility RF frequencies were not initially synchronized between
rings when injecting at same rigidity 28 MHz acceleration system, h = 360 197 MHz storage system, h = 2520 (= 7360)
DX
IP
DX
Beam-beam ON Beam-beam OFFBeam-beam OFF
v=5m·frf
Moving crossing points if frf0
W. Fischer
20 m
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 10/21
Tune Modulation From Moving Crossing PointTune Modulation From Moving Crossing Point
W. Fischer
T revolution time h harmonic number frf radio frequency frf difference between two rings
Example 1: RHIC Au-Au frf = 28 MHz, frf = 5 Hz vCP = 27 m/s modulated interaction
Example 2: RHIC d-Au, same rigidity at injection frf = 28 MHz, frf = 44 kHz vCP = 3 m/turn pseudo-random interaction
Distance between DX magnets is 16 m
Longitudinal velocityof crossing point
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 11/21
Beam Loss from Unequal RF Frequencies at InjectionBeam Loss from Unequal RF Frequencies at Injection
Beam-beam effect during injection, d and Au with same rigidity
frf = 44kHz, vertical separation was 10 mm ( 10) in all IRs
Pseudo-random dipole kicks lead to emittance increase
Very
mod
est
inte
nsit
ies!
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 12/21
DX Magnet Geometries for Ramp DesignDX Magnet Geometries for Ramp Design
DX magnets had unipolar shunts reversed for lower field Injection with equal rigidity 1 mrad crossing angle Injection/store with equal frequency 1 mrad common angle
Zero-degree calorimeter lumi monitors moved by 1 cm
ZDC moved by 1 cm
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 13/21
Acceleration Ramp and OpticsAcceleration Ramp and Optics
Final production acceleration ramp and optics Different B at injection/store, same RF frequency through ramp Modest * due to concerns about DX outer edge aperture
800
0 50 100 150 200 250Time [seconds]
0
2
4
6
8
10
0
200
400
600
* [
m]
B[
T-m
, B
lue a
nd Y
ello
w r
ings]
Tra
nsi
tion
Sto
rage
Inje
ctio
n
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 14/21
120 Bunches and Beam-Beam Background120 Bunches and Beam-Beam Background
Transition losses seed pressure bumps in PHOBOS/BRAHMS Small pressure bumps in STAR/PHENIX, not transition seeded RHIC dAu: removed transverse separation then cogged
SY. Zhang
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 15/21
120 Bunches and PHOBOS Pressure Burst120 Bunches and PHOBOS Pressure Burst
Pressure rise in interaction areas varied quasi-exponentially with total beam current electron cloud pressure rise
No pressure rise seen in solenoidal field detectors PHOBOS background/radiation very sensitive to IR pressure burst
Total Normalized Beam Intensity90 140
Vacu
um
Pre
ssure
[Torr
]1
e-
10
1e-
6
0
Pressure rise [10-9 Torr]1.2
PH
OB
OS B
ack
gro
und [
Hz]
0
450
SY. Zhang
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 16/21
Transverse microwave instabilities while rampingTransverse microwave instabilities while ramping
01:53:43
01:53:44
Wit
h I
nsta
bilit
y
Wit
hou
t In
sta
bilit
y
Single-bunch transverse instability monitor later in run No multibunch instability monitoring/coupled bunch
damping Correlated with emittance growth; retuned chroms to
fix
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 17/21
Typical RHIC dAu StoresTypical RHIC dAu Stores
dAu luminosity lifetime about 1.5h, dominated by Au IBS Higher intensity d beam likely suffered less from beam-beam Au debunching resolved with RF noise fix, additional RF voltage
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 18/21
RHIC dAu Integrated LuminosityRHIC dAu Integrated Luminosity
PHENIX last two weeks:
4.58 nb-1/weekBest 2-3 day periods:7-9 nb-1/week @ PHENIX/STAR
Fixed instabilityPHOBOS to
b*=4m
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 19/21
RHIC dAu Performance LimitationsRHIC dAu Performance Limitations
Vacuum pressure rise Total intensity apparently limited to 100-110 109 Au equivalent Limits deuteron-gold operations to 56 bunches/ring NEG
coatings Transition instabilities
Coherent bunch oscillations drive beam growth/reduce luminosity Corrected with machine tuning Feb 23 in deuteron beam
Longitudinal instabilities Leads to factors 2–3 in diamond size, Landau cavities 200 MHz RF driver noise fixed during run
Au beam intensity/lifetime IBS, Transverse/longitudinal emittance growth Electron cooling
Startup time, finding “best conditions” for operation Balance between stability/development, experiments/operations Flexibly determine, switch to “good” conditions for production 2 days to change ramp from same rigidity to same frequency
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 20/21
RHIC dAu ConclusionsRHIC dAu Conclusions
Nearly all significant program challenges were overcome Injector mode switching between d/Au worked well Tandem redundancy problems were not an issue Deuteron intensities well beyond goal with bunch merging
Injectors contained surprises with low Z/A Constant Bp injection did not work due to modulated
beam-beam interaction issuesRequired development of cross-ring RF frequency
locking, new ramps developed in a few days Ramp design of common dipole orbits can hold surprises
1 mrad common angle, limited * to maintain aperture Transverse instability diagnosis/fix improved luminosity by
factor of two
Already talk of a possible second RHIC dAu run
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 21/21
AcknowledgementsAcknowledgements
Many thanks to…
Thomas Roser, Johannes van Zeijts, Wolfram Fischer
L. Ahrens, M. Bai, M. Blaskiewicz, J.M. Brennan, P. Cameron, A. Drees, H. Huang, H.C. Hseuh, P. Ingrassia, U. Iriso, Y. Luo, Y. Makdisi, G. Marr, W.W.MacKay, R. Michnoff, C. Montag, F. Pilat, V. Ptitsyn, R. Tomas, D. Trbojevic
…and of course all RHIC Operations teams
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 22/21
================================================
Spare slides
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 23/21
RHIC Achieved and Planned ParametersRHIC Achieved and Planned Parameters
[best store or week]
[incl. beam studiesand maintenance]
Mode No ofbunche
s
Ions/bunch
[9]
*[m]
Emittance
[ m]
Lpeak
[cm-2s-1] Lstore ave
[cm-2s-1] Lweek Time
inStore
Au-Au design 56 1 2 15-40 91026 21026 50 b-1 --
p-p design 56 100 2 20 51030 41030 1.2 pb-1 --
Au-Au [Run-2]
55 0.7 1 15-40 61026 11026 15 b-1 26%
d-Au [Run-3]
55 (110)
110d/0.7Au
1 15 121028 31028 4.5 nb-1 31%
Au-Au [Run-4]
45 1.1 1 15-40 151026 51026 160 b-1 53%
p-p [Run-4] *
28 170 1 20 151030 101030 0.9 pb- 1 n/a
Au-Au upgrade
112 1.1 1 15-40 361026 91026 350 b-1 60%
p-p upgrade*
112 200 1 20 801030 651030 25 pb-1 60%* Achieved polarization performance in p-p Run-4 was 40-45% in store* Planned polarization performance by p-p enhanced is 70% in store
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 24/21
Machine Challenges at RHICMachine Challenges at RHIC
More flexibility than at other hadron colliders Variation in particle species, including asymmetric operations
So far Au+Au, d+Au, p+p, p+p, Cu+Cu Variation in energy, energy scans
d+Au at 100 GeV/u Au+Au, Cu+Cu at 10, 31, 65, 100 GeV/u p+p at 100 GeV (250 GeV planned in 2006)
Variation in lattice Low * in most cases (0.8-3 m) Polarity change in experimental magnets ~ every 2 weeks
Short runs (~30 weeks/year), with multiple modes Very short amount of set-up time (2-3 weeks) required
Four experiments (2 large, 1-2 small) Work to avoid single-experiment bottlenecks
Short luminosity lifetime with heavy ions (IBS, ~ few hours) Fast refills essential
May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 25/21