1 Machine issues for RHIC II Wolfram Fischer PANIC Satellite Meeting – New Frontiers at RHIC 30 October 2005

Wolfram Fischer 2 Content 1.Machine status, Enhanced Luminosity (2008) 2.Electron Beam Ion Source (EBIS) 3.RHIC II motivation and goals Luminosity Setup-time Energy variation Species

Wolfram Fischer 3 RHIC status

Wolfram Fischer 4 RHIC status Since 2000: 4 ion combinations 7 energies 46% polarization

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

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

Wolfram Fischer 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  p

Wolfram Fischer 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, 3 He 

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

Wolfram Fischer 10 RHIC II – Motivation Debunching requires continuous abort gap cleaning Luminosity lifetime requires frequent refills Ultimately need cooling at full energy Intensities Luminosities   2.5h 0.5h1.5h Beam and luminosity lifetime for Au – Au dominated by IBS [Factor 10 between Au an p]

Wolfram Fischer 11 RHIC II – electron cooling at store Possible layout in RHIC (magnetized) Superconducting gun Challenge: electron cooling time   7/2 (magnetized) or   2 (un-magnetized) [1 st cooling in a collider – high brightness, high power ERL] Need : 54 MeV, mA (= 5-10 MW) Existing: 88 MeV, 9 mA ( Jefferson Lab ERL for IR FEL) MW e-beam

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

Wolfram Fischer 13 Gold collisions (100 GeV/n  100 GeV/n): w/o e-coolingwith e-cooling Emittance (95%)  m15   10 Beta function at IR [m] Number of bunches Bunch population [10 9 ]11  0.3 Beam-beam parameter per IR Peak luminosity [10 26 cm -2 s -1 ]3290 Ave. store luminosity [10 26 cm -2 s -1 ]870 Polarized proton collision (250 GeV  250 GeV): Emittance (95%)  m2012 Beta function at IR [m] Number of bunches Bunch population [10 11 ]22 Beam-beam parameter per IR Ave. store luminosity [10 30 cm -2 s -1 ] RHIC II Luminosities with Electron Cooling

Wolfram Fischer 14 Maximum luminosity estimates: p-p, Au-Au, U-U

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

Wolfram Fischer 16 Setup times for different modes Achieved initial ion setup in 2.5 weeks  may reach 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

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

Wolfram Fischer 18 Luminosity at different energies – ions L   2 for  s  200 GeV/n without cooling [projections document] –  from energy dependent beam size –  from from aperture limited in triplets Light ions at low energies can be cooled. Gain over above scaling depends on species, energy, and probably running time per mode. No operation possible near transition.

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

Wolfram Fischer 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  increase, loose about same amount with small crossing angle) [W.W. MacKay et al., “Feasibility of increasing the energy of RHIC”, PAC 2001]

Wolfram Fischer 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  2  increased effects of IBS, space charge, persistent current magnetic field errors (not measured), instabilities 15% below current injection , no rf matching  bunch length will increase stronger than with  -scaling Cooling potentially very effective (low  )  Not yet included in current electron and stochastic cooling plans, needs study Need to test AGS extraction/RHIC injection at reduced energy

Wolfram Fischer 22 RHIC II pp luminosities with electron cooling pp luminosity limited by beam-beam effect  Cannot exceed certain brightness N b /  N Cooling at store not effective (cooling time  Z 2 /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

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

Wolfram Fischer 24 RHIC II – technically constrained timeline Establish feasibility: early 2006 Start construction: 2009 Begin commissioning: 2012 Based on simulations and assessment of critical component parameters (SC gun, SC ERL)

Wolfram Fischer 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 U 92+, polarized 3 He 2+ and possibly polarized d + (difficult) Collision energy range can be somewhat extended (upwards by ~30%, downwards by ~50%)