1. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 BNL R&D ERL and Coherent Electron Cooling test at RHIC Outline Goals of R&D ERL at BNL ERL general layout and main components Coherent electron cooling test at RHIC Plans & Conclusions

2. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 PHENIX STAR e-cooling (RHIC II) Four e-beam passes e + storage ring 5 GeV - 1/4 RHIC circumference Main ERL (3.9 GeV per pass) Introduction R&D ERL will serve as a test-bed for future RHIC projects: ERL-based electron cooling (conventional or coherent), 10-to-20 GeV ERL for lepton-ion collider eRHIC. It will also address general issues expanding capabilities of ERLs: novel SRF injector, high current and high brightness beam ERL operation, flexible lattice to enable covering a vast operational parameter space.

3. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 Goals for ERL R&D at BNL Test the key components of the High Current Energy Recovery Linac based solely on SRF technology –703.75 MHz SRF gun test with 500 mA –high current 5-cell SRF linac test with HOM absorbers Single turn - 500 mA –test the beam current stability criteria for CW beam currents –Demonstrate beam quality close to that required for high energy electron cooling Test the attainable ranges of electron beam parameters in SRF ERL

4. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 50 kW 703.75 MHz system Control room Cryo-module SRF cavity 1 MW 703.75 MHz Klystron e - 2.5MeV Laser SC RF Gun e - 2.5 MeV Beam dump Cryo-module e - 15-20 MeV Schematic Layout of the ERL Merger system Return loop

5. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 Half cell SRF Gun A. M. M. Todd et al., “State-of-the-Art Electron Guns and Injector Designs for Energy Recovery Linacs”,PAC2005 SC RF Gun: shape and axial electric field profile (SUPERFISH result) f RF = 703.75 MHz Energy=2.5-3 MeV Average Current: 0.5 A Two fundamental power couplers: 0.5 MW each Electron beam energy gain at the exit of the gun versus initial phase SC RF Gun: axial electric field profile for different cathode insertion depth (SUPERFISH result)

6. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 BNL R&D ERL SRF Injector layout SRF Gun SRF Linac Z-merger Dipoles Solenoids ERL Loop Dipole

7. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 Evolution of normalized beam emittances in the BNL R&D ERL injector 15º -15º -30º 99.5 cm 70 cm 30º SC RF Gun 5 cell SC RF cavity Blue 5 nC Red 1.4 nCGreen 0.7 nC 4.8/5.3 um 2.2/2.3 um1.4/1.4um HorizontalVertical BNL ERL Injector: beam dynamics simulation results

8. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 ERL: loop layout 2-3 MeV 20 MeV 2-3 MeV SC RF Gun SC 5 Cell cavity Beam dump Modes of operationCritical parameters High energy acceptanceLow dispersion, large aperture Beam break up instability studyAdjustable transverse phase advance Longitudinal motion studyAdjustable longitudinal dispersion Two pass acceleration Changeable path length

9. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 ERL loop lattice is very flexible Lattice  and D functions of the ERL for the different cases longitudinal dispersions (Ds=M56): Positive longitudinal dispersion Negative longitudinal dispersion Zero longitudinal dispersion No dispersion Dispersion, m , m Transverse normalized emittances from cathode to dump Q=0.7 nC (PARMELA simulation)

10. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 BNL 5 Cell SRF Cavity Design F = 703.75 MHz,  E = 20 MeV Q 0 ~ 10 10, Q HOM ~ 10 3 The 5-cell cavity was specifically designed for high current, high bunch charge applications such as eRHIC and high energy electron cooling. The loss factor of the cavity was minimized. The number of cells was limited to 5 to avoid HOM trapping. Additionally, HOM power is effectively evacuated from the cavity via an enlarged beam pipe piece 24 cm diameter. Build: AES Processed: JLAB Arrived at BNL

11. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 Cavity VTA tests low temp. bake The cavity was processed at JLab. After BCP, Rinsing, and low temp. bake (120 C) (120 C) cavity reached 19 MeV/m at Q 0 =10 10. 19 MeV/m E beam,max  20 MeV

12. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 HOM measurements The damping of the Q-values is 2 orders of magnitude. Results well agree with simulations. Several dipole modes at frequencies below 1 GHz were measured and could be identified by comparison with simulation results The simulated BBU threshold is of the order of 20 A for the nominal designed ERL lattice and simulated HOM parameters. GBBU and TDBBU codes were used.

13. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 R&D ERL beam parameters High Current High charge Charge per bunch, nC0.71.45 Numbers of passes111 Energy maximum/injection, MeV20/2.5 20/3.0 Bunch rep-rate, MHz7003509.383 Average current, mA500 50 Injected/ejected beam power, MW1.0 0.15 R.m.s. Normalized emittances ex/ey, mm*mrad1.4/1.42.2/2.34.8/5.3 R.m.s. Energy spread,  E/E 3.5x10 -3 5x10 -3 1x10 -2 R.m.s. Bunch length, ps182131 Operation regime Parameter

14. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 2-3 MeV 20 MeV 2-3 MeV SC RF Gun SC 5 Cell cavity Beam dump BPM DCCT 1MW Klystron SRF Linac 50 kW Transmitter ready to operate Arc assembly QuadrupoleDipole Tested in BLD912 Arrived, test this summer Measured, ready to be installed ERL Enclosure (Vault) was constructed 5-cell Cavity is being processed and tested at JLAB, arrived in March, 2008 The dumping of HOM Q-values measured 2 orders of magnitude 1 MW Gun klystron and 50 kW 5-cell cavity transmitter are installed Recirculation loop magnets and vacuum system components have arrived Injection dipoles are under magnetic measurements Gun drive laser is been procured Gun is under construction at AES BNL R&D ERL: Status

15. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 R&D ERL Commissioning Milestones and beyond Coherent Electron Cooling Proof of Principal Test around 2012

16. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 Modifications from R&D ERL to P-o-P CEC Move SRF Gun, 5cell cavity, loop arcs and injection line from 912 to IR2 Stretch straight line in order to accommodate cooling section (modulator- undulator-kicker ) ~15 m Build and install 7 m undulator Bldg 912 IR2

17. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 SC 5 Cell cavitySC 5 Cell cavity IR-2 for proof-of-principle for CEC 19.6 m RHIC Beam RHIC lattice functions IR2 7 m 4 m electron and ion beams

18. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 Electron beam lattice functions for CEC PoP test at RHIC UNDULATOR Modulator region Kicker region

19. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 Q=1.4 nC, 100% : dE/E=4.8x10 -3, ex/ey=5.6/6.7 um 80% : dE/E=1.3x10 -3, ex/ey=5.4/5.6 um BNL R&D ERL electron beam longitudinal profile The electron bunch is +/-15 degrees of RF For CEC: emittance requirements are relax The energy spread is important Some injection line modification may be applied

20. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 CEC proof of principal at RHIC setup Au bunch intensity1E09 Z/A79/197 Energy40 GeV/n RMS normalized emittances 2.5 mm-mrad RMS energy Spread4E-04 RMS bunch length66 cm Beta*10 m Electron bunch charge5 nC (4x1.4nC) Energy21.7 MeV RMS normalized emittances 5 mm-mrad RMS Energy Spread0.15 % Beta*5 m  pe, CMF 5.0 E09 Hz Modulator length L1,m4 m Number of plasma oscillations 0.256 Ion bunch parametersElectron bunch parameters

21. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 CEC proof of principal at RHIC setup (cont.) ww 5 cm Undulator length7 m B1.2 kGauss Beta_und1 m awaw 0.555  FEL 18  m Amplitude gain G =150, L w 7 m IBS rate9 min Cooling time, beam,2.6 minutes FEL parameters Cooling parameters Electron bunches are usually much shorter that the hadron bunches and cooling time for the entire bunch is proportional to the bunch-lengths ratios The formula gives very encouraged result More simulations and accurate studies are under way Ion bunch: 2.5E-09 sec Electron bunch: 50E-12 sec Kicker length, L23 m Cooling time, local, minimum0.05 minutes

22. 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23 Plans & Conclusions Design of major ERL components is completed. Hardware components are being manufactured and/or procured. We plan to start commissioning of the R&D ERL in 2009 First, we develop the straight pass (gun -- 5 cell cavity -- beam stop) test for the SRF Gun performance studies. Next, a novel concept of emittance preservation in a beam merger at the lower energy will be tested After recirculation loop completed, demonstrate energy recovery of high charge and high current beam The prototype will serve as a test bed for studying issues relevant for very high current ERLs (since 2010) Proof of principle coherent electron cooling ions in RHIC at ~ 40 GeV/n is feasible with existing R&D ERL parameter and should be demonstrate around 2012