1. BROOKHAVEN SCIENCE ASSOCIATES 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

2. BROOKHAVEN SCIENCE ASSOCIATES RHIC Operations and Plans Run 1: FY 200028 wks Au-Au (130 GeV/A) Run 2:FY 2001-0240 wks Au-Au (200 GeV/A) p↑-p↑ (200 GeV) Run 3:FY 200329 wks d-Au (200 GeV/A) p↑-p↑ (200 GeV) ~30% Pol. Run 4:FY 200427 wks Au-Au (200, 62 GeV/A)p↑-p↑ (200 GeV) Run 5:FY 200532 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. BROOKHAVEN SCIENCE ASSOCIATES First Five Years of RHIC Experiments 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

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

5. BROOKHAVEN SCIENCE ASSOCIATES Control of Emittance Growth: Cooling 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

6. BROOKHAVEN SCIENCE ASSOCIATES The Objectives of RHIC e-Cooling and Challenges ~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 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.

7. BROOKHAVEN SCIENCE ASSOCIATES 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 7x10 26 to ~7x10 27 cm -2 s -1 )

8. BROOKHAVEN SCIENCE ASSOCIATES Parameters for of RHIC Magnetized e-cooling 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 –f SRF : 703.5 MHz –Repetition rate: 9.4 MHz Cooling solenoids: 2 x 40m long B = 5T,  B/B < 10 -5 Collider operation: Collisions at 3 IPs,  *=0.5m, 112 bunches

9. BROOKHAVEN SCIENCE ASSOCIATES N e /bunch=3*10 11 w/ cooling.  *=0.5m w/o cooling,  *=1m Simulation for Au-Au at 100 GeV/A Luminosities per IP in cm -2 sec -1 vs. time in seconds The luminosity gain may be limited either by the collision beam burn out or the beam-beam parameter X, Y, Z Distribution (  )

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

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

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

14. BROOKHAVEN SCIENCE ASSOCIATES 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. BROOKHAVEN SCIENCE ASSOCIATES 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. BROOKHAVEN SCIENCE ASSOCIATES Non-magnetized Cooling: Simulation Au-Au at 100 GeV/A Magnetized Cooling Non-magnetized Cooling: Luminosity Non-magnetized Cooling: Emittance Non-magnetized Cooling: Bunch Length

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

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

19. BROOKHAVEN SCIENCE ASSOCIATES 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. BROOKHAVEN SCIENCE ASSOCIATES RHIC e-Cooling Project Milestones & Collaborations 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