RHIC - the high luminosity hadron collider

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1 RHIC - the high luminosity hadron collider RHIC overview Luminosity and polarization evolution Performance limitations Future upgrades RHIC II luminosity upgrade erhic Thomas Roser MIT seminar November 30, 2004

2 NSRL 2 superconducting rings 3.8 km circumference

3 A Mini-Bang: Nuclear matter at extreme temperatures and density Colliding gold at GeV/nucleon (40 TeV total cm energy) Plus: other species (p-p, Cu-Cu (Run-5), ) asymmetric collisions (d-au, p-au (?)) several energies ( , 65+65, 32+32, 10+10) a. Formation phase - parton scattering b. Hot and dense phase - quark-gluon plasma and hadron gas? strongly interacting hot dense material (sqgp) c. Freeze-out emission of hadrons Produce and explore a new state of matter

4 Hard Scattering at RHIC pp data Central Au+Au collisions p+p jet+jet (STAR 200 GeV) Au+Au??? (STAR 200 GeV/nucleon pair)

5 RHIC Spin Physics Spinning Quarks or Gluons Spinning Proton Spinning Proton Quark, Gluon, Photon, Electron or Neutrino from W or Z Decay Spin structure functions of gluon and anti-quarks Parity violation in parton-parton scattering Requires high beam polarization and high luminosity

6 Gold Ion Collisions in RHIC Beam Energy = 100 GeV/u RHIC 9 GeV/u Q = +79 BOOSTER AGS TANDEMS 1 MeV/u Q = +32

7 Mode RHIC design, achieved and enhanced design parameters No of bunches Ions/bunch [10 9 ] β* [m] Beam polarization Design values (1999) L peak [cm -2 s -1 ] Au Au p p Achieved values (2004) Au Au p p % A 1 A 2 L store ave [cm -2 s -1 ] p p Enhance design values (2008) L store ave [cm -2 s -1 ] Au Au p p % L = 3 freve 2M N BN * εβ 2 Other high luminosity hadron colliders: achieved goal scaled to 200 GeV Tevatron (2 TeV) LHC (14 TeV)

8 RHIC luminosity evolution Nucleon-pair luminosity A 1 A 2 L allows comparison of different species. Luminosity increased by 2 orders of magnitude in 4 years.

9 A day of RHIC operations (Feb. 23, 2004) Injector RHIC

10 Performance Limitations Intra-beam scattering (heavy ions) Dynamic pressure rises Instabilities Beam-beam (light ions and protons) Polarization (protons)

11 Luminosity Limit Intra-Beam Scattering (IBS) Intensities Luminosities τ 2.5h 0.5h 1.5h Debunching requires continuous gap cleaning (tune meter) Luminosity lifetime requires frequent refills Ultimately need cooling at full energy

12 Intra-Beam Scattering (IBS) in RHIC Longitudinal and transverse emittance growth agrees well with model Some additional source of transverse emittance growth Deuteron and gold beams are different because of IBS

13 Bunched Beam Stochastic Cooling Microwave stochastic cooling (4-8 GHz) should work for longitudinal cooling and limit beam debunching due to IBS during store Longitudinal bunched-beam Schottky spectra during store (100 GeV): Protons: persistent coherence interferes with cooling Test planned for Run-5. Gold: no persistent coherence (IBS) debunched beam visible

14 Luminosity Limits Dynamic Pressure Rises p + total, p + /bunch, 110 bunches, 108 ns spacing electron density and pressure rise 12 min total beam intensity All operational relevant pressure rises can be explained by electron clouds NEG (non-evaporative getter) coated beam pipes installed in warm areas Ubaldo Iriso

15 Luminosity Limits Fast Instability Near Transition Fast transverse instability (~ GHz) High sensitivity around transition Effect of broadband impedance, electron cloud (?) Cures: beam-beam tune spread, octupoles, cross zero-chromaticity before transition (why?) Tomographic reconstruction of 2D bunch density Before instability After instability with ~ 10 ms growth rate

16 Luminosity Limits Beam-Beam Interaction Beam lifetime with different number of collisions, ξ=0.003/ip (due to abort gaps some bunches see only 2 or 3 collisions per turn)

17 Luminosity Limits Beam-Beam Interaction RHIC 4096 is the turn first spectrahadron collider to see coherent beam-beam effects Experiment: - single p bunch/ring - ξ = Q x,b Q x,y < Observation: - π x -mode shift: expectation: 1.21 ξ = [Yokoya, Meller, Siemann] No operational problem so far.

18 Luminosity Limits Betatron Tune Working Point Tried several working points: [.18,.19] (RHIC design) [.22,.23] (RHIC init. ops.) [.31,.32] (LHC design) [.68,.69] (SppbarS ops.) [.73,.74] (?) [.68,.69] is best. It improves collision lifetime and polarization transmission/lifetime Beam-beam tune spread with 2 collisions Q y Loss rate working point during store working point during ramp R. Tomas, M. Bai Q x snake resonance orbit resonance

19 RHIC polarized proton accelerator complex Absolute Polarimeter (H jet) PHOBOS RHIC pc Polarimeters BRAHMS & PP2PP PHENIX Siberian Snakes STAR Siberian Snakes Spin Rotators (longitudinal polarization) Pol. H - Solenoid Partial Siberian Snake Source LINAC BOOSTER Spin Rotators (longitudinal polarization) Spin flipper Helical Partial Siberian Snake 200 MeV Polarimeter AGS AGS Internal Polarimeter Rf Dipole Strong AGS Snake AGS pc Polarimeters Installed and commissioned during FY04 run Plan to be commissioned during FY05 run Plan to be installed and commissioned during FY05 run

20 Proton polarization at the AGS raw asymmetry = A N P B Full spin flip at all imperfection and strong intrinsic resonances using partial Siberian snake and rf dipole Ramp measurement with new AGS pc CNI polarimeter: Vertical Polarization Experiment data (2000) Simulation (2000) Experiment data (2002) Simulation and measurement at 25 GeV Simulation (2002) Experiment data (2003) Simulation Simulation (2003) (2003) 0+ν y 24 ν y 12+ν y 36 ν y 24+ν y 48 ν y 36+ν y G γ Remaining polarization loss from coupling and weak intrinsic resonances New helical partial snake (RIKEN funded) eliminated coupling resonances To avoid all depolarization in AGS build strong AGS helical Siberian snake!

21 Strong Partial Siberian Snake in AGS Imperfection resonance Polarization partial snake resonance Intrinsic resonance desired vertical betatron tune to avoid depolarization Challenges: 1. SC element in warm machine 2. Lattice disturbances

22 New AGS helical snakes 2.6 m 5 % helical snake build at Tokana Industries funded by RIKEN. Cold strong snake eliminates all depolarizing resonances in AGS. Warm snake avoids polarization mismatch at AGS injection and extraction. 2.6 m 30% s.c. helical snake build at SMD (AIP) Installation: Jan. 2005

23 Siberian Snake in RHIC Tunnel Siberian Snake: 4 superconducting helical dipoles, 4Tesla, 2.4 m long with full 360 twist Funded by RIKEN, Japan Designed and constructed at BNL

24 Acceleration and squeeze ramp 60 Polarization survival in RHIC Spin rotator ramp % Polarization Luminosity cm -2 s -1 Protons x :00 07:00 08:00 09:00 10:00 11:00

25 RHIC II luminosity upgrade Eliminate beam blow-up from intra-beam scattering with electron beam cooling at full energy! What will remain the same: 120 bunch pattern 100 ns collision spacing ( ~ same data acquisition system) Only one beam collision between DX magnets 20 m magnet-free space for detectors No mini-beta quadrupoles Approx. the same bunch intensity No new vacuum or instability issues Background similar as before upgrade What changes: Smaller transverse and longitudinal emittance Smaller vertex region Beta squeeze during store to level luminosity Store length is limited to ~ 5 hours by burn-off due to Au-Au interactions (~ 200 b)

26 Electron cooling and IBS Intra-Beam Scattering: The ions collide with each other, leading to accumulation of random energy (heat) derived from the guide fields and the beam s energy. Electron cooling: The high-current high-brightness electron beam from an ERL will cool the RHIC ions in a highprecision, 26 m long superconducting solenoid.

27 RHIC electron cooling Au ions in RHIC are 100 times more energetic than in a typical cooler ring. Relativistic factors slow the cooling by a factor of γ 2. Cooling power needs to be a factor of γ 2 higher than typical. Bunched electron beam requirements for 100 GeV/u gold beams: E = 54 MeV, <I> ~ 100 ma, electron beam power: ~ 5 MW! Requires high brightness, high power, energy recovering superconducting linac, as demonstrated by JLab for IR FEL. (50 MeV, 5 ma) First linac based, bunched electron beam cooling system used at a collider

28 Future RHIC upgrades electron cooling R&D Superconducting ERL Buncher Cavity Debuncher Cavity Cooling Solenoids (2 x 13m, 2-5 T) Gold beam Benchmarking of IBS and cooling simulation codes Demonstrate high precision (<10 ppm) solenoid (2-5 T) Demonstrate 20 nc, ma MHz CW SCRF electron gun Develop MHz CW superconducting cavity for high intensity beams Build R&D Energy Recovering Linac (ERL)

29 RHIC Future Luminosity RHIC upgrades with and electron without cooling Cooling 100 Luminosity leveling through continuously adjusted cooling Luminosity, cm -2 s With e-cooling Without e-cooling Store length limited to 4 hours by burn-off Four IRs with two at high luminosity Time, hours Transverse beam profile during store Also may be able to pre-cool polarized protons at injection energy 2 mm 5 hours

30 RHIC II Luminosities with Electron Cooling Gold collisions (100 GeV/n x 100 GeV/n): w/o e-cooling with e-cooling Emittance (95%) πµm Beta function at IR [m] Number of bunches Bunch population [10 9 ] Beam-beam parameter per IR Ave. store luminosity [10 26 cm -2 s -1 ] 8 70 Pol. Proton Collision (250 GeV x 250 GeV): Emittance (95%) πµm Beta function at IR [m] Number of bunches Bunch population [10 11 ] 2 2 Beam-beam parameter per IR ? Ave. store luminosity [10 32 cm -2 s -1 ]

31 CW Photo-cathode and Superconducting rf Gun R&D Emission enhancement (x 30-80) using a diamond window Initial design for a superconducting gun with diamond amplified photo-cathode. Ilan Ben-Zvi et al. Cavity Tuner Cathode insert on choke joint Liquid helium

32 703.8 MHz CW Superconducting Cavity for High Intensity Beams 4 RF shielded gate valve HOM ferrite dampers Tuner location 2K main line Space frame support structure Large bore cavity Vacuum vessel 2K fill line Outer magnetic shield Thermal shield Inner magnetic shield He vessel Fundamental Power Coupler assembly Cold model tested successfully

33 Solenoid R&D: <10 ppm Directional Uniformity BEAM SPLITTER MAGNETIC NEEDLE OPTICAL FILTER LASER MIRROR POSITION SENSITIVE DETECTOR Dipole Corrector 5 T design started Copper Solenoid 18 mt; 1.83 m long

34 Electron-Ion Collider at RHIC: erhic 10 GeV, 0.5 A e-ring with ¼ of RHIC circumference (similar to PEP II HER) 10 GeV electron beam s 1/2 for e-a : 63 GeV/u; s 1/2 for e -p : 100 GeV Existing RHIC interaction region allows for typical asymmetric detector Luminosity: up to cm 2 s 1 per nucleon BNL, MIT Bates collaboration

35 Alternative Design: Linac - Ring (V. Litvinenko, I. Ben-Zvi, et al) Electron ring replaced by energy-recovering linac, electrons in RHIC arcs + no hadron beam effect on electrons (single pass), simpler IR design, multiple IRs possible, 20 GeV upgrade - no positrons possible, cost

36 Summary Since 2000 RHIC has collided, for the first time, Heavy ions Light on heavy ions Polarized protons (45% beam polarization) Heavy ion luminosity increased by factor 100 For next 4 years planned: Factor 2 increase in heavy ion luminosity Factor 2 increase in proton beam polarization Factor 40 increase in proton luminosity Future upgrades: RHIC luminosity upgrade using electron cooling at store Electron-ion collider erhic