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RHIC Operations and Plans

Electron Cooling at RHIC Enhancement of Average Luminosity for Heavy Ion Collisions at RHIC R&D Plans and Simulation Studies 8 th ICFA Seminar Kyungpook Natioanl University Daegu, Korea, September 29, 2005 Satoshi Ozaki for the RHIC e-Cool Team Brookhaven National Laboratory.

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RHIC Operations and Plans

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  1. Electron Cooling at RHICEnhancement of Average Luminosity for Heavy Ion Collisions at RHICR&D Plans and Simulation Studies8th ICFA SeminarKyungpook Natioanl UniversityDaegu, Korea, September 29, 2005Satoshi Ozaki for the RHIC e-Cool TeamBrookhaven National Laboratory

  2. RHIC Operations and Plans • Run 1: FY 2000 28 wks Au-Au (130 GeV/A) • Run 2: FY 2001-02 40 wks Au-Au (200 GeV/A) p↑-p↑ (200 GeV) • Run 3: FY 2003 29 wks d-Au (200 GeV/A) p↑-p↑ (200 GeV) ~30% Pol. • Run 4: FY 2004 27 wks Au-Au (200, 62 GeV/A) p↑-p↑ (200 GeV) • Run 5: FY 2005 32 wks Cu-Cu (200, 62 GeV/A) p↑-p↑ (200 GeV) ~50% Pol Near term improvements in progress • Superconducting helical snakes in the AGS for higher polarization for FY 2006 Runs • Development of EBIS ion source for flexibility of ion operation

  3. The luminosity performance of RHIC for Au-Au & Cu-Cu collisions exceeded the design values. We observed creation of a new state of matter in Au-Au collisions at 200 GeV/A collision energy: hot, dense and strongly coupled, behaving like perfect fluid. Next stage of the program: Study properties of the new state of matter Study of rare processes  Requires much higher average/integrated luminosity First Five Years of RHIC Experiments

  4. Typical Au-Au Operation on Feb. 23, 2004 Au Beam Intensity vs. Time Au-Au Luminosity vs. Time

  5. The Au-Au luminosity life-time is only a few hours Strong intra-beam scatterings cause emittance growth: Longitudinal: loss of ions from colliding buckets Transverse: larger crossing beam spot size Cooling of ion beams: the key to a longer luminosity life-time: i.e., a higher average luminosity Cooling: Stochastic cooling: more effective for hot beam Difficult for bunched Proton beams but it appears that it can work for heavy ion beams in RHIC Longitudinal cooling test in preparation Electron cooling: more effective for cool beam It has been successful at lower energies but has not been demonstrated at high energy like RHIC Control of Emittance Growth: Cooling

  6. The Objectives of RHIC e-Cooling and Challenges • Cooling rate slows in proportion to 7/2. • Energy of electrons needed (54 MeV) is well above DC accelerators. • Requires bunched e beam. • Need exceptionally high electron bunch charge and low emittance. • Need ERL to provide low emittance e-beam while maintaining a reasonable power demand. • ~10 times Increase of RHIC average luminosity for Au-Au at 100 GeV/A • Reduce background due to beam loss • Keep short collision diamond by maintaining short bunch length to match detector’s acceptance

  7. R&D: Theory Issues • We must understand cooling physics in a new regime: • understanding IBS, recombination, disintegration • binary collision simulations for benchmarking • experimental benchmarking of the magnetized cooling efficiency issues • Cooling dynamics simulations with precision • A good estimate of the luminosity gain is essential. • Simulations show that: 10X increase in the average luminosity can be achieved (from 7x1026 to ~7x1027 cm-2s-1)

  8. Parameters for of RHIC Magnetized e-cooling • Cooling solenoids: • 2 x 40m long • B = 5T, B/B < 10-5 • Collider operation: • Collisions at 3 IPs, • *=0.5m, • 112 bunches Key e-beam parameters: • Bunch charge: q = 20nC • E-Beam Energy = 54MeV • E/E < 3x10-4 • Emittance: 50m-rad • Magnetization: 380mm.mr Energy Recovery Linac • fSRF:703.5 MHz • Repetition rate: 9.4 MHz

  9. Simulation for Au-Au at 100 GeV/A Ne/bunch=3*1011 w/ cooling. *=0.5m w/o cooling, *=1m Luminosities per IP in cm-2sec-1 vs. time in seconds X, Y, Z Distribution () The luminosity gain may be limited either by the collision beam burn out or the beam-beam parameter

  10. R&D: ERL and Cooling Hardware Issues • Development of a high current low emittance RF Gun: • photocathode, laser, etc. • Design of a high current & very low emittance ERL • Development of beam diagnostics • Beam dynamics studies • Further refinements of simulation codes • Development of high field solenoid with B/B<105

  11. Laser Photocathode S/C RF Gun: Key to performance 1 ½ cell gun designed for cooler ½ cell gun prototype: Under construction

  12. Diamond Amplified Photocathode • Electron Amplifying Diamond Window • Less demanding on laser power • Longer cathode life • Protect SC cavities from contamination

  13. Gun Z-bend merger ERL ←Compressor Stretcher→ Cooling solenoids in RHIC ring Schematics for Magnetized Beam ERL Lattice Beam Dump

  14. The Possibility of Non-magnetized Electron Cooling • Handling of magnetized beams is not easy, and the system is complex and expensive. • At high , achievable solenoid error limits the cooling speed of the magnetized cooling. Another way is the non-magnetized e-cooling: • A study showed that sufficient cooling rates can be achieved with non-magnetized cooling. • Recombination beam loss is a concern but can be managed to be small enough to assure a long luminosity life-time • By reduced bunch charge • By larger beam size • Helical undulator can further reduce recombination* *Suggested by Derbenev, and independently by Litvinenko

  15. Non-magnetized Cooling: Parameters Beam Parameters: • Rms momentum spread of electrons =10-3 • Rms normalized emittance: 2.5 µmrad • Rms radius of electron beam in cooling section: 2.5 mm • Rms bunch length: 5 cm • Charge per bunch: 5nC (cf. 20nC for magnetized case) • Cooling sections: 2x30 m • Large ion beam in the cooling section: β* = 200 m All ERL technology developments for mag-cool applies here but • without complex magnetized electron beam gun, • without bunch stretcher and compressor, and • without complex beam optics to preserve magnetization

  16. Au-Au at 100 GeV/A Non-magnetized Cooling: Simulation Non-magnetized Cooling: Luminosity Magnetized Cooling Non-magnetized Cooling: Emittance Non-magnetized Cooling: Bunch Length

  17. Beam Intensity Time (sec) Beam Loss Comparison: Simulation Recombination: ON Undulators: OFF Recombination: Off Undulators: Off Undulator parameters: 50 Gauss, 5 cm period, Radius of rotation 1.7 m Recombination: ON Undulators: ON

  18. R&D ERL Under Construction To study the issues of high-brightness, high-current electron beams as needed for RHIC II and eRHIC.

  19. SRF Cavity for High Current (Ampere Class) ERL 703.5 MHz 5 Cell Cavity with Beam Tune HOM Damping: Built by Advanced Energy Systems Inc. of Long Island

  20. 2005 Dec: Electron cooling simulation completed 2006 Jan: Decision on the cooling method 2006 Feb: High power rf system for the gun in place 2006 Apr: 5-cell superconducting cavity delivered 2006: Beam dynamics simulation 2006: Cost and Schedule of e-cooling system for CD0 2007 Mar: Begin testing S/C gun, hopefully with the diamond cathode 2008: Hope to begin testing of ERL hardware The Milestones subject to the future funding level Collaborators: BINP, JINR, Celsius, GSI. US Jefferson Lab, Fermilab, Indiana Univ., and industry (AES and Tech-X) Supported by: the U.S. DOE, Division of Nuclear Physics, and partially by the U.S. DOD HE Laser Joint Tech Office and ONR RHIC e-Cooling Project Milestones & Collaborations

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