Prospects for RHIC Low-Energy Operations Todd Satogata (W. Fischer, T. Roser, A. Fedotov, N. Tsoupas, M. Brennan, C. Montag, and others) “Can We Discover the QCD Critical Point at RHIC?” Workshop March 9, 2006 Scope and History Initial Machine Projections Operational Challenges Recommendations

March 9, 2006T. Satogata - RHIC Low-Energy Operations2 ScopeScope  The workshop is motivated by a growing body of theoretical and experimental evidence that the critical point on the QCD phase diagram, if it exists, should appear on the QGP transition boundary at baryo-chemical potential ~ MeV, corresponding to heavy ion collisions with c.m. energy in the range  s= GeV/u.  Beam total energy in RHIC of GeV/u RHIC momentum aperture typically 1-3x10 -3  Assume Au as the primary, but not necessarily only, species 2.5 GeV/u total energy scales very badly as Z/A increases  For reference, normal Au injection total energy is 9.8 GeV/u Can likely inject up to ~12GeV/u  Provide projections, identify primary challenges  Below injection energy: field quality, IBS, emittance, cooling  Above injection energy: ramping, transition energy

March 9, 2006T. Satogata - RHIC Low-Energy Operations 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

March 9, 2006T. Satogata - RHIC Low-Energy Operations4 Initial Machine Projections  Scaling laws apply above injection energies  When aperture dominated:  Peak luminosity   2  No clear scaling laws apply below injection energies  Injected beam already fills aperture  Magnetic field quality degrades very quickly  Power supply regulation  Strawman model  Peak luminosity   3-4

March 9, 2006T. Satogata - RHIC Low-Energy Operations5 Initial 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  Projections do not include potential improvements  Electron and stochastic cooling (peak and integrated luminosity)  Lattice modifications to mitigate IBS (integrated luminosity)  Total bunch intensity from vacuum improvements (peak luminosity)  Small set of specific energies (and species?) should be a workshop deliverable for planning

March 9, 2006T. Satogata - RHIC Low-Energy Operations6 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  Low-current magnet measurements are a priority Total Energy  BB Dipole Current 9.8 GeV/u A 2.5 GeV/u A

March 9, 2006T. Satogata - RHIC Low-Energy Operations7 Power Supply Regulation Issues  Several power supply issues  Chromaticity sextupoles  Main power supplies  Sextupoles: A -> A  CMOS regulation, works to 0.01 A  Study option of using only some sextupoles with higher current  Aperture and lifetime concerns  Correction of large main dipole b 2  Main dipoles: 430 A -> 110 A  Requires testing to check regulation  Will test during Run6 maintenance  Pulsed injection/extraction kickers  May have low-voltage limitations

March 9, 2006T. Satogata - RHIC Low-Energy Operations8 Other Issues for Beam Energies GeV/u  Injector issues (also covered by Nick Tsoupas)  Au at 2.5 GeV/u is above AGS injection energy (1.0 GeV/u)  AGS Au transition energy is 8 GeV/u  AGS/ATR extraction aperture dominated by G10 kicker  IBS growth rates (from Alexei Fedotov)  Consistent with 30-minute stores at 5 GeV/u  Lower energies likely require cooling or lattice modifications Beam Energy [GeV/u] IBS growth time [s] (horizontal) 2300 (longitudinal)

March 9, 2006T. Satogata - RHIC Low-Energy Operations9 Beam Studies for Low-Energy Injection  ~1 day of studies required in run before low-energy operations  Initial studies  Trivially scale nominal injection to lower energies  Provides reality check of power supplies, optics  Test injection, establish circulating beam, optimize lifetime  Initial global optics measurements, field quality, tune scan, energy resolution/momentum aperture  IBS growth time study require 3-6 hours extra time All but IBS growth evaluation can be done with Run6 p  Later studies  IBS modification lattice development  Field quality and detailed optics measurement/correction

March 9, 2006T. Satogata - RHIC Low-Energy Operations10 Issues for Beam Energies GeV/u  Raising RHIC injection energy  Limited by injection kicker performance, ~20% increase feasible with 55 bunches  Higher energies than ~12 GeV/u require RHIC ramping  Squeeze  * with acceleration to maintain constant aperture  2-3 days of setup per energy is probably sufficient  Optimize operations for length of stores/ramping time  Nominal RHIC transition energy:    21.3 for Au  Operation at  near   is infeasible  Lattice modifications using   -jump power supplies Successful in Run 6, lowered   by ~1 unit

March 9, 2006T. Satogata - RHIC Low-Energy Operations11 Transition Energy Modification  For Run 6, transition energy was successfully modified  Lowering polarized proton injection energy for spin matching  Nominal    23.5, modified    22.8  Primarily changes horizontal dispersion, momentum aperture  No effort to tune dispersion matching, limit triplet dispersion Modified Nominal

March 9, 2006T. Satogata - RHIC Low-Energy Operations12 Cooling at Low Energies  Stochastic cooling is feasible but requires development  Different mixing regime than high-energy stochastic cooling  Cannot use filter cooling, as Schottky bands overlap  Higher cooling rates at lower energies, but requires different method Cooling rate estimates under development  Palmer cooling  Under active development at C-AD as frontier of cooling Will test cutting chord from pickup to kicker in Run 7  Requires new cold pickup in arc (high dispersion, low beta)  Concerns about 10 Hz coherenct signal rejection  Electron cooling discussed in Alexei’s talk

March 9, 2006T. Satogata - RHIC Low-Energy Operations13 SummarySummary  No apparent show-stoppers for RHIC collisions at  s=5-50 GeV/u  Lattice modifications to suppress IBS should be studied  For beam energies GeV/u, luminosity scaling is uncertain  Field quality at very low currents should be measured/modeled   *=10m likely required for reasonable lifetime/aperture  IBS drives very short store times (<30 min) below 4-5 GeV/u  A ~1 day study period in preceding run will be very beneficial Identify power supply, lifetime, tuning issues/limitations  Above GeV/u, luminosity scales as  2 with constant aperture  Study transition energy changes Required to avoid ~3 GeV transition “hole” around GeV/u  Very similar to normal heavy ion operations, 2-3 days setup/energy  Low-energy cooling  Stochastic Palmer cooling under development, unknown cooling time  Electron cooling is quite promising (see A. Fedotov’s talk)