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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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Presentation on theme: "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,"— Presentation transcript:

1 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

2 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience2/21 The RHIC Layout  RHIC rings are independent except for DX magnets  4.3T, 180mm aperture “combiner” magnet between two rings  Design bend angle is mrad  Deuteron Z/A=0.5, not far from Au Z/A=0.4  no need to move DX magnets Blue Ring Yellow Ring AGS MP6MP7 Tandems Booster Linac RHIC STAR PHENIX PHOBOSBRAHMS dAu DX D0

3 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience3/21 Program 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 period PerformanceGoalAchieved Setup/Ramp-up time [days]14/2118/20 days Storage energy [GeV/u]100 Number of bunches55110/55  * [m]22/3/4 Diamond length  [cm]2015 Peak luminosity [x10 28 cm -2 s -1 ] Average luminosity (store) [x10 28 cm -2 s -1 ] Integrated luminosity (week) [nb -1 /week]4.04.6

4 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience4/21 Program Goals, Achievements, Challenges  Many challenges for a short run  Injector performance and mode switching  Ramp design issues  Inject at constant B , then constant frequency  Common 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 ParameterAu GoalAu Achievedd Goald Achieved Intensity/bunch1.0x x x x10 11 Total intensity (55/110 bunches)55x /60x x /69x10 11 Transverse emittance (95%,   rad) Bunch length [ns]55 55

5 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience5/21 Injector 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

6 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience6/21 Deuteron Booster Challenges  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; 12  4 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.  8  4 bunch merge in AGS doubled total intensity Deuteron Booster bunch merge RF harmonic h=2 to h=1 Deuteron intensity: 5-6x10 10 to 1-1.1x10 11

7 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience7/21 Single-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 start  New species (d) always contain surprises  Au was almost always single-bunch limited  Later resolved to be heavy ion injector septum aperture  Tandem/source inconsistency apparent late in run  Deuteron bunch merge worked well in last month of run

8 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience8/21 Total Intensity Run Performance  Pushed bunch # since single-bunch intensity was limited  Maximum total intensity 60-65x10 9 Au, near ecloud limit  Deuteron max total intensity around 70x10 11 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

9 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience9/21 Injection at Same Rigidity  Blue and Yellow rings independent (except DX)  Inject at same rigidity in both rings, different f rf  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 (= 7  360) DX IP DX Beam-beam ONBeam-beam OFF v=5m·  f rf Moving crossing points if  f rf  0 W. Fischer 20 m

10 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience10/21 Tune Modulation From Moving Crossing Point W. Fischer Trevolution time hharmonic number f rf radio frequency  f rf difference between two rings Example 1: RHIC Au-Au f rf = 28 MHz,  f rf = 5 Hz  v CP = 27 m/s  modulated interaction Example 2: RHIC d-Au, same rigidity at injection f rf = 28 MHz,  f rf = 44 kHz  v CP = 3 m/turn  pseudo-random interaction Distance between DX magnets is 16 m Longitudinal velocity of crossing point

11 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience11/21 Beam Loss from Unequal RF Frequencies at Injection  Beam-beam effect during injection, d and Au with same rigidity  f rf = 44kHz, vertical separation was 10 mm (  10  ) in all IRs  Pseudo-random dipole kicks lead to emittance increase Very modest intensities!

12 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience12/21 DX 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

13 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience13/21 Acceleration 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 Time [seconds]  * [m] B  [T-m, Blue and Yellow rings] Transition StorageInjection

14 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience14/ 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

15 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience15/ 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 Intensity Vacuum Pressure [Torr] 1e-10 1e-6 0 Pressure rise [10 -9 Torr] 1.2 PHOBOS Background [Hz] SY. Zhang

16 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience16/21 Transverse microwave instabilities while ramping 01:53:4 3 01:53:44 With Instability Without Instability  Single-bunch transverse instability monitor later in run  No multibunch instability monitoring/coupled bunch damping  Correlated with emittance growth; retuned chroms to fix

17 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience17/21 Typical 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

18 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience18/21 RHIC dAu Integrated Luminosity PHENIX last two weeks: 4.58 nb -1 /week Best 2-3 day periods: 7-9 nb -1 PHENIX/STAR Fixed instability PHOBOS to b*=4m

19 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience19/21 RHIC dAu Performance Limitations  Vacuum pressure rise  Total intensity apparently limited to 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

20 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience20/21 RHIC 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 issues  Required 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

21 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience21/21 Acknowledgements 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

22 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience22/21 ========================  Spare slides

23 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience23/21 RHIC Achieved and Planned Parameters [best store or week] [incl. beam studies and maintenance] ModeNo of bunches Ions/bunch [  9 ]  * [m] Emittance [   m] L peak [cm -2 s -1 ] L store ave [cm -2 s -1 ] L week Time in Store Au-Au design    b p-p design   pb Au-Au [Run-2]    b -1 26% d-Au [Run-3]55 (110)110d/0.7Au11512   nb -1 31% Au-Au [Run-4]    b -1 53% p  -p  [Run-4] *   pb - 1 n/a Au-Au upgrade    b -1 60% p  -p  upgrade*   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

24 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience24/21 Machine 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

25 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience25/21 Booster Injection/Extraction, AGS Injection Parameters C. Gardner

26 May 25, 2005T. Satogata - RHIC Deuteron-Gold Experience26/21 AGS Extraction, RHIC Ramp Parameters C. Gardner


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