RHIC Low-Energy Au Test Run Summary Todd Satogata L. Ahrens, M. Bai, J.M. Brennan, D. Bruno, J. Butler, B. Christie, A. Drees, A. Fedotov, W. Fischer, P. Harvey, T. Hayes, W. Jappe, R.C. Lee, M. Leitch, W. W. MacKay, N. Malitsky, G. Marr, R. Michnoff, B. Oerter, F. Severino, K. Smith, S. Tepikian, N. Tsoupas,... June 11, 2007 Scope and Background Challenges Highlights and Results

June 11, 2007T. Satogata - RHIC Low-Energy Test Run2 ScopeScope  Significant experimental interest in RHIC heavy ion collisions with c.m. energy in the range  s= 5-50 AGeV  Corresponds to Au beam  =2.68 to 26.8  Nominal Au injection is  =10.52, already below design  =12.6  Low-energy luminosity and lumi lifetime difficult to extrapolate  Test run with protons Jun was quite successful  Open machine issues  How does machine field quality degrade at lower energies?  Can we correct optics with current power supply configuration? Main issue presently chromaticity control  Are any power supply regulation/hardware changes required?  How do we test changes necessary for RHIC RF? Main issue is change of RHIC harmonic number  What luminosity can be measured with low-energy collisions? Main deliverable: luminosity measurement at low energy

June 11, 2007T. Satogata - RHIC Low-Energy Test Run3 March 2006 RIKEN Workshop Accelerator Summary  No apparent show-stoppers for RHIC collisions at E cm = 5-50 GeV/n  Only equal energies  Unequal species possible only if minimum rigidity > 200 T-m  Without cooling  long vertex distribution  Small set of specific energies (and species?) should be a workshop deliverable for planning:  2.5,3.2,3.8,4.4… GeV/n total beam energy  Studies that should be done soon:  A ~1 day study period at low total beam energy to identify power supply, lifetime, tuning issues/limitations  Low-current superconducting magnet measurements  Pre-cooling in AGS  10x luminosity ?  Electron cooling would make this a fantastic facility: ~100x luminosity, small vertex distribution, long stores. Expected whole vertex minbias event rate [Hz] T. Roser, T. Satogata RHIC Heavy Ion Collisions Which scaling do we use?

June 11, 2007T. Satogata - RHIC Low-Energy Test Run4 Proton/Gold parameters at same rigidity ProtonsGold (eq)  s [GeV] Beam energy [GeV] Beam kinetic energy [GeV] Relativistic  Relativistic  Momentum [GeV/c] B  [T-m]37.40 Injection current scaling Main dipole current [A]217.7 Main quad current [A]202.6 Revolution frequency [Hz] RF frequency [MHz, h=366]  Use same rigidity as 2006 for 2007 test run  Magnet strengths are same  May adjust tunes to Au tunes  Still need to do RF capture  Gives greatest time to work on three major outstanding issues  RF harmonic number h=366  Luminosity measurement  Chromaticity control  IBS lifetime estimate: 1800s RHIC RF frequency range is MHz

June 11, 2007T. Satogata - RHIC Low-Energy Test Run5 Setup Challenges: RHIC h=366  LLRF (Hayes, Smith, Severino, Harvey)  LLRF code modified, clocks set to h=366  AGS to RHIC synchro set up, inject pattern race condition avoided  RF capture easily achieved using peak detectors  Beam Sync Clocks (Michnoff, Jappe, Oerter)  Required h=366 for experiment crossing clocks  Event generators reconfigured to avoid h=360 automatic revtick  Invalid events apparently generated every turn: Kerner module PLL?  New fake lower priority revtick inserted, driven by RF h=366 signal  V124 clocks to experiments fortunately “wrapped around” at h=360  Fill Pattern  Can only fill up to 120 bucket pattern, or buckets divisible by 3  Cannot easily generate same number of collisions at STAR/PHENIX  PHENIX: 1-1, 4-4,... gives STAR 1-123, 4-126,... crossing patterns

June 11, 2007T. Satogata - RHIC Low-Energy Test Run6  s = GeV/u RHIC RF (  =4.93)  Can barely fit “good” Au longitudinal emittance in RF bucket, h=366  Lower energies will have immediate debunched beam

June 11, 2007T. Satogata - RHIC Low-Energy Test Run7 Run Chronology, June  RF/Timing setup occurred during maintenance day  20:15: RHIC ready for beam with Au76n (yo9-qd9 swap), 500kV RF  20:15-00:30: Abort kicker issues, not reacting to dump events  Resolved in blue with resets, yellow by clearing V125 pet page on each injection  02:30: Circulating unbunched beam in both rings  03:00: BPMs rough-timed in both rings; half strength orbit correction  03:45: Good lifetime for RF setup  05:00: RF phase detectors working, RF capture in both rings  08:00: Work on beam stability/lifetime, first look at collision signals  10:00: AC dipole optics taken for both rings, strong octupoles turned on  12:00: DX BPMs timed in, PHENIX/STAR steered  12:30: Real STAR collision signals observed  13:05: 111 bunch injection attempt fails; back off to 56 bunch  13:00-15:00: Three vernier scans at STAR, PHENIX timing/DAQ problems  15:00-16:00: Tandem downtime, Blue spurious QLI  16:00: End of Low Energy Test Run 2007, total beam time 14.5 hours

June 11, 2007T. Satogata - RHIC Low-Energy Test Run8 Beam Lifetime Intensity [Au e9] minutes  Double exponential fit to beam lifetimes  Fast component lifetime: ~2 minutes  Slow component lifetime: ~20 minutes (consistent with IBS prediction)  Observed debunching in some stores Debunching

June 11, 2007T. Satogata - RHIC Low-Energy Test Run9 Chromaticity and Stability  Unipolar defocusing sextupoles were driven to zero in both rings  Beams still metastable, stabilized with octupole settings  Future runs should consider reversing defocusing sextupole supplies

June 11, 2007T. Satogata - RHIC Low-Energy Test Run10 Bunch Lengths Low Energy InjectionNominal Injection 20 ns  Bunch lengths nearly same!  Injection efficiency 80-90% in both rings  Capture efficiency 100%, beam clearly fit in bucket  Requires further analysis...

June 11, 2007T. Satogata - RHIC Low-Energy Test Run11 STAR Vernier Scans STAR BBC Coinc 0 +/-6mm Vernier Scan /-9mm Vernier Scan Au Beam [e9] 0 35 Few Losses!

June 11, 2007T. Satogata - RHIC Low-Energy Test Run12 Sample STAR data Run : (TPC gain low) BBC-small triggers BBC-Large triggers both bbc s&l - 1 vpd triggers (+ bbc s&l) W. Christie

June 11, 2007T. Satogata - RHIC Low-Energy Test Run13 Challenges and Successes  Challenges  h=366 invalid events stopped PHENIX, nearly stopped STAR, interfered with V125 abort trigger module  3-bucket cogging in h=366 prevented simultaneous expt cogging  Unipolar defocusing sextupoles limited chromaticity to near zero  Minor online model issues prevented full range of tune adjustment  All challenges are addressible either offline or during test run setup  Successes  LLRF worked like a charm, RF capture quick with phase detectors  Instrumentation worked remarkably well with h=366 timing  Orbit correction, coupling corrections worked well  Longitudinal beam distribution shorter than expected (scraping?)  Vernier scans still feasible even with 2-20 minute beam lifetimes  Have data for luminosity measurement deliverable

June 11, 2007T. Satogata - RHIC Low-Energy Test Run14 Other low-energy testing options Gold  s [GeV] Beam energy [GeV] Beam kinetic energy [GeV] Relativistic  Relativistic  Momentum [GeV/c] B  [T-m] Injection current scaling Main dipole current [A] Main quad current [A] Revolution frequency [Hz] RF harmonic number RF frequency [MHz]  Each new energy likely requires ~4-6h setup  Injection, RF, chrom...  RF issues dominate  Does beam fit in RF bucket?  May be able to throw away intensity in AGS  Optics and IBS measurements  Additional luminosity points for projections?

June 11, 2007T. Satogata - RHIC Low-Energy Test Run15 ==============================

June 11, 2007T. Satogata - RHIC Low-Energy Test Run16  s = GeV/u AGS RF  AGS RF can be well-matched to RHIC RF for this energy  30 ns bunch lengths may be an issue for detector acceptance

June 11, 2007T. Satogata - RHIC Low-Energy Test Run17 Low-Energy Proton Test Run Results (June )   s =22.5 GeV, 47% of normal proton main magnet currents  First injection to circulating beam in about 30 minutes (both rings)  Circulating beam to RF capture in under 3 hours.  Injection efficiency was about 70-80%.  Beam lifetimes of 5-10h (not in collision) and 4-5h (in collision) achieved.  Chromaticities and instabilities could barely be controlled with existing power supplies at this energy. New sextupole families should permit better chromaticity control for a 2007 test run.  Proton emittances out of AGS were very good (<10 pi mm mrad normalized) Measured emittances in RHIC were comparable as long as beams did not go unstable.  Optics measurements and correction data were taken in both rings. Analysis shows that optics (beta functions, phases, dispersions) are quite close to the model, so linear field quality is not limiting performance.  Two hours were spent performing vernier scans in PHENIX and STAR with beam-beam counters. Lack of good luminosity monitoring made this inconclusive.

June 11, 2007T. Satogata - RHIC Low-Energy Test Run GeV/u Au collisions  2 days of 9.8 GeV/u collisions  0.4  b -1 integrated luminosity   *=3m by necessity  minute stores  56 Au bunches, 0.6x10 9 /bunch  Hz ZDC rates  IBS and aperture dominated beam and luminosity lifetime  Another run at this energy may improve this by factor of 2-5  x10 9 /bunch  Raise  * to improve lifetime  RHIC is best used as a storage ring collider below beam energies of ~12 GeV/u

June 11, 2007T. Satogata - RHIC Low-Energy Test Run19 Low-Energy Machine Projections ModeBeam Energy [GeV/u] N bunches Ions/bunch [  9 ]  * [m] Emittance [  m] L peak [cm -2 s -1 ] Au-Au  Au-Au  Au-Au  Au-Au  Au-Au   Assumes expected luminosity scaling as  3 below 9.8 GeV/u   */aperture and integrated luminosity tradeoffs must be studied

June 11, 2007T. Satogata - RHIC Low-Energy Test Run20 Low-Energy Magnetic Field Quality  Magnet currents scale with rigidity B  which scale with   Field quality deteriorates rapidly at very low currents  Currently have no magnet measurements at very low currents, few at low energy  Must extrapolate field behavior for simulations Total Energy  BB Dipole Current 9.8 GeV/u A 2.5 GeV/u A