Prospects for RHIC Low-Energy Prospects for RHIC Low-Energy Operations Operations Todd SatogataTodd Satogata

(W. Fischer, T. Roser, A. Fedotov, N. Tsoupas, M. Brennan, C. Montag, and others)(W. Fischer, T. Roser, A. Fedotov, N. Tsoupas, M. Brennan, C. Montag, and others)

“Can We Discover the QCD Critical Point at RHIC?” “Can We Discover the QCD Critical Point at RHIC?” WorkshopWorkshop

March 9, 2006March 9, 2006

• Scope and History• Initial Machine Projections• Operational Challenges• Recommendations

March 9, 2006 T. Satogata - RHIC Low-Energy Operations 2

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 ~100 - 500 MeV, corresponding to heavy ion collisions with c.m. energy in the range s= 5 - 50 GeV/u. Beam total energy in RHIC of 2.5-25 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, 2006 T. Satogata - RHIC Low-Energy Operations 3

2001 9.8 GeV/u Au collisions2001 9.8 GeV/u Au collisions

2 days of 9.8 GeV/u collisions 0.4 b-1 integrated luminosity *=3m by necessity 60-90 minute stores 56 Au bunches, 0.6x109/bunch 10-30 Hz ZDC rates IBS and aperture dominated

beam and luminosity lifetime

Another run at this energy may improve this by factor of 2-5 1.0+x109/bunch Raise * to improve lifetime

RHIC is best used as a storage ring collider below beam energies of ~12 GeV/u

March 9, 2006 T. Satogata - RHIC Low-Energy Operations 4

Initial Machine ProjectionsInitial 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, 2006 T. Satogata - RHIC Low-Energy Operations 5

Initial Machine ProjectionsInitial Machine Projections

Mode Beam Energy[GeV/u]

Nbunches Ions/bunch [9]

*[m]

Emittance[m]

Lpeak

[cm-2s-1]Au-Au 2001-2 9.8 55 0.6 3 15 8.01024

Au-Au 2003-4 31.2 45 1.0 3 15-30 1.21026

Au-Au 9.8 55 1.2 10 15-40 1.01025

Au-Au 2.5 55 1.0 10 15-30 1.11023

Au-Au 25 55 1.2 3 15-40 2.01026

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, 2006 T. Satogata - RHIC Low-Energy Operations 6

Low-Energy Magnetic Field QualityLow-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

TotalEnergy

B Dipole Curren

t9.8 GeV/u 10.5

281.11 430 A

2.5 GeV/u 2.68 20.69 110 A

March 9, 2006 T. Satogata - RHIC Low-Energy Operations 7

Power Supply Regulation IssuesPower Supply Regulation Issues

Several power supply issues Chromaticity sextupoles Main power supplies

Sextupoles: 0.6-0.7 A -> 0.15-0.2 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 b2

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, 2006 T. Satogata - RHIC Low-Energy Operations 8

Other Issues for Beam Energies 2.5-10 GeV/uOther Issues for Beam Energies 2.5-10 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]

2.5 2505 18009 5000 (horizontal)

2300 (longitudinal)

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

Beam Studies for Low-Energy InjectionBeam 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, 2006 T. Satogata - RHIC Low-Energy Operations 10

Issues for Beam Energies 10-25 GeV/uIssues for Beam Energies 10-25 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, 2006 T. Satogata - RHIC Low-Energy Operations 11

Transition Energy ModificationTransition 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

ModifiedNominal

March 9, 2006 T. Satogata - RHIC Low-Energy Operations 12

Cooling at Low EnergiesCooling 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, 2006 T. Satogata - RHIC Low-Energy Operations 13

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 2.5-10 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 10-12 GeV/u, luminosity scales as 2 with constant aperture Study transition energy changes

• Required to avoid ~3 GeV transition “hole” around 20-23 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)