Machine issues for RHIC II

1. Machine issues for RHIC II Wolfram Fischer PANIC Satellite Meeting – New Frontiers at RHIC30 October 2005

2. Content • Machine status, Enhanced Luminosity (2008) • Electron Beam Ion Source (EBIS) • RHIC II motivation and goals • Luminosity • Setup-time • Energy variation • Species

3. RHIC status

4. RHIC status • Since 2000: • 4 ion combinations • 7 energies • 46% polarization

5. RHIC status Luminosity increased by 2 orders of magnitude in 4 years.

6. RHIC – Enhanced Luminosity goals – 2008 For Au-Au, average per store, 4 IRs L = 81026cm-2s-1 at 100GeV/u For p-p average per store, 2 IRs L = 61031cm-2s-1 at 100GeVL = 1.51032cm-2s-1 at 250GeVwith 70% polarization 4 design2 achieved 16 design 9 achieved 1 design 1.5 achieved

7. Enhanced Luminosity Upgrades For all species: Completion of RHIC vacuum upgrade to suppress e-clouds • Warm: installation of NEG coated beam pipes • Cold : additional pumping before cool-down For polarized protons: Full commissioning of AGS cold snake • Leading to 85% spin transmission • At design bunch intensity 21011p

8. EBIS Electron Beam Ion Source replaces existing 35-year old Tandems (2009) Main advantages: • No Tandem reliability upgrade needed • Simpler operation at reduced costs • Simpler Booster injection (fewer turns at higher energy) • Faster species switching (d-Au in sec instead of 5min) • New species: U, 3He

9. EBIS EBIS Tandem-to-Booster: 840mEBIS-to-Booster : 30m J. Alessi Tandem

10. Intensities Luminosities t 2.5h 0.5h 1.5h RHIC II – Motivation Beam andluminositylifetime for Au – Au dominated by IBS [Factor 10 between Au an p] • Debunching requires continuous abort gap cleaning • Luminosity lifetime requires frequent refills • Ultimately need cooling at full energy

11. RHIC II – electron cooling at store Challenge: electron cooling time  g7/2 (magnetized) or  g2 (un-magnetized) [1st cooling in a collider – high brightness, high power ERL] Need : 54 MeV, 100-200 mA (= 5-10 MW) Existing: 88 MeV, 9 mA (Jefferson Lab ERL for IR FEL) Superconducting gun MW e-beam Possible layout in RHIC(magnetized)

12. RHIC II – luminosity evolution Luminosity leveling through continuously adjusted cooling Store length limited to 4 hours by “burn-off” Four IRs with two at high luminosity with e-cooling without e-cooling Transverse beam profile during store Also may be able to pre-cool polarized protons at injection energy 5 hours 2 mm

13. RHIC II Luminosities with Electron Cooling Gold collisions (100 GeV/n  100 GeV/n): w/o e-cooling with e-cooling Emittance (95%) mm 15  40 15  10 Beta function at IR [m] 1.0 1.0 Number of bunches 112 112 Bunch population [109] 1 1  0.3 Beam-beam parameter per IR 0.0016 0.004 Peak luminosity [1026 cm-2s-1] 32 90 Ave. store luminosity [1026 cm-2s-1] 8 70 Polarized proton collision (250 GeV  250 GeV): Emittance (95%) mm 20 12 Beta function at IR [m] 1.0 0.5 Number of bunches 112 112 Bunch population [1011] 2 2 Beam-beam parameter per IR 0.007 0.012 Ave. store luminosity [1030 cm-2s-1] 150 500

14. Maximum luminosity estimates: p-p, Au-Au, U-U

15. Maximum luminosity estimates: Si-Si, Cu-Cu, d-Au, p-Au

16. Setup times for different modes • Achieved initial ion setup in 2.5 weeks may reach 1-1.5 weeks (excluding major downtime) • Achieved reduction in energy in 2-3 days may reach 1 day (excluding major downtime) • Achieved polarized pp setup in 3 weeks may reach 1-2 weeks (excluding major downtime) • Achieved ramp-up to maximum luminosity in physics in 4-5 weeks some improvement possible

17. Asymmetric collisions • For p-Au collisions need to move DX magnets,not necessary for d-Au collisions • Need to have same revolution frequencies (g)for both beamsinjection/ramp: no modulated beam-beam (problem for LHC, although smaller bunch intensity)store : maintains luminosity and vertex • 250GeV p on 100GeV/n Au: not possibleequal frev not possible, expect luminosity reduction of at least 1000 • Can possibly collide 120GeV p on 100GeV/n Auexpect considerable operational difficulties

18. Luminosity at different energies – ions L  g2 for s  200 GeV/n without cooling [projections document] • g from energy dependent beam size • g from from aperture limited in triplets No operation possible near transition. Light ions at low energies can be cooled. Gain over above scalingdepends on species, energy, and probably running time per mode.

19. 2% for s = 63GeV (b*=3.5m) Luminosity at different energies – polarized protons L  g2 for s  500 GeV [b*=0.5m at s = 500 GeV] • g from energy dependent beam size • g from from aperture limited in triplets

20. Luminosities at different energies – above current maximum • Dipoles have margin of up to 30%(may be only 20%) Operation may be possible up to s = 650 GeV • Most of magnets(quadrupoles, snakes, …)also have margin • DX magnets don’t have margin • 1.3 mrad crossing angle with current strength • 18 mrad crossing angle without DX • Luminosity close to luminosity for s = 500 GeV(gain 30% with g-increase, loose about same amount with small crossing angle) [W.W. MacKay et al., “Feasibility of increasing the energy of RHIC”, PAC 2001]

21. Luminosity at different energies – below current minimum • No hard limit down to 2.3GeV/n  100A in main dipoles – inject now at 472A • Luminosity will deteriorate faster than g2 increased effects of IBS, space charge, persistent current magnetic field errors (not measured), instabilities • 15% below current injection g, no rf matching bunch length will increase stronger than with g-scaling • Cooling potentially very effective (low g) Not yet included in current electron and stochastic cooling plans, needs study • Need to test AGS extraction/RHIC injection at reduced energy

22. RHIC II pp luminosities with electron cooling • pp luminosity limited by beam-beam effect  Cannot exceed certain brightness Nb/eN • Cooling at store not effective (cooling time Z2/A) Pre-cooling at injection to increase brightness • Expect only small improvements in polarization after AGS cold snake fully operational 70%+ average polarization at store

23. Polarized species other then protons (with EBIS options) • Polarized d+ • Would need new RFQ or source (~$0.5m) • Intensity : 11011/bunch • Polarization : needs study, longitudinal difficult • Luminosity scale factor : 0.5Lpp • Polarized 3He2+ • Intensity : up to 21011/bunch • Polarization : ~ 15% < than p • Luminosity scale factor : 1Lpp

24. RHIC II – technically constrained timeline Establish feasibility : early 2006 Start construction : 2009 Begin commissioning : 2012 Based on simulationsand assessment of critical componentparameters (SC gun, SC ERL)

25. Summary RHIC II • Main technology for RHIC II: electron cooling could be commission by 2012 (technically constrained) • Expected luminosity increase (over Enhanced Luminosity) • 10 for Au-Au • 2-3 for polarized protons • Expect small improvements in polarization,and setup time • With EBIS can have beams of U92+, polarized 3He2+ and possibly polarized d+ (difficult) • Collision energy range can be somewhat extended (upwards by ~30%, downwards by ~50%)