1. Chris Tennant Jefferson Laboratory March 15, 2013 “Workshop to Explore Physics Opportunities with Intense, Polarized Electron Beams up to 300 MeV”

2. Outline  Review of the Jefferson Lab FEL Driver  Upgrade scenarios Flexible machine, many options available  Present capabilities DarkLight experiment  Preliminary S2E for low charge understanding low-charge operation  Experimental hall transport line Fixed-target experimental program  Capabilities of RF drive  Incorporating a polarized injector Maintain high-charge gun capabilities  Key Components  Summary

3. Jefferson Lab FEL Driver: 2 ERLs DC Gun SRF Linac UV FEL Transport Line Dump IR Wiggler Bunching Chicane THz Line  350 keV DC photocathode gun, 9 MeV booster, Penner bend merge  3-cryomodule linac  Bates-bend arcs  longitudinal matching/bunch compression in chicane for IR arc/bypass for UV (“chicaneless”)  energy compression during recovery  nonlinear compaction management IR FEL: 14+ kW at 1.6 microns, several kW at multiple wavelengths UV FEL: High power (100+ W) at 70 and 400 nm, coherent harmonics into VUV (10 eV) THz Beamline: 10s of W at (0.2-1.5) THz

4. Upgrade Scenarios DL Upgrade 100 MV Cryomodule Two 100 MV Cryomodules Polarized e - Injector RF Drive (300 kW) Experimental Hall Transport Line Energy (MeV) 1-pass 2-pass Repetition Freq. (MHz) Linac RF Power (kW) Polarization 75 120 No 260 750 300 130 180 360 Yes 300 600

5. DarkLight Experiment  450 kW (4.5 mA CW at 100 MeV) through 2 mm aperture for 8 hours  Clean transmission, low beam loss (6 ppm)  Achieved small beam size (50 μm rms)  (Note: performed at 60 pC/bunch) 1 mm  x = 50  m  y = 52  m (courtesy P. Evtushenko)

6. DarkLight with 20 pC  20 pC injector solution, optimized for beam brightness (courtesy Fay Hannon)  Transverse emittance preserved (< 1 mm-mrad)

7. DarkLight with 20 pC  x,y = 11.5 um  Physical phase space at the location of the DarkLight cube

8. Longitudinal Match 30 ps 1.9 MeV AB C D B B C C D D A B C D

9. Beam Quality Issues at Low Charge  Coherent Synchrotron Radiation should not be an issue; reduced charge, no bunch compression  Space charge charge density may be comparable  Halo Due to flexibility of machine, have some level of control  Low-charge operation Beam can become very bright, care must be taken with longitudinal phase space which can become “spindly/thready”

10. Transport Line to Experimental Hall  Avoid interferences with lab infrastructure for new (fixed- target) experimental hall  Need a spectrometer to phase linac for 1-pass operation  Preserve beam quality (courtesy D. Douglas)

11. Capabilities: 120 kW RF Drive 20 pC at 75 MHz 2 pC at 750 MHz 2.7 pC at 75 MHz 0.27 pC at 750 MHz

12. Capabilities: 300 kW RF Drive 50 pC at 75 MHz 5 pC at 750 MHz 6.7 pC at 75 MHz 0.67 pC at 750 MHz

13. Polarized Electron Injector  Want to retain functionality of current gun – which is optimized for high charge install gun within FEL “ring” and use 180° arc to merge to linac 200 kV 350 kV (under construction)

14. Polarized Injector: Merger  4-quad matching section + 4-period FODO arc

15. Polarized Injector: Merger  Push 100K particles through with PARMELA Suffers no significant transverse emittance degradation The arc has M 56 = 0.25 m; with initial chirp on bunch from booster, beam gets compressed  a good thing

16. Longitudinal Match A B C D 10 ps B C D 0.4 MeV A B B C C D D

17. Energy Spread at Linac Exit  E full = 1.8 x 10 -3  E full = 1.5 x 10 -2 Current merger Arc merger (polarized source)

18. Key Components to Upgrade(s) Polarized Gun: new generation gun design (350 kV) DC Power Supply: Drive Laser: Buncher: reuse from FEL injector (soon to be replaced) Booster: reuse from FEL injector (soon to be replaced) Merger Design: FODO arc to allow placement of gun within FEL ring Injector Merger  Currently, the machine can provide unpolarized beam for internal target experiments (e.g. DarkLight)  To support a fixed-target program with polarized beam requires:

19. Key Components to Upgrade(s) Cryomodules: 100 MV module by end of 2013; increase energy further by adding two more refurbished cryomodules RF Power: installing 12 GeV klystrons would increase our capacity from 120 kW (8 kW klystrons) to 300 kW (12 kW klystrons) Recirculator: though specified for 80-210 MeV operation, with modification to the temperature of the cooling water, the hardware is capable of operating at 300 MeV Experimental Hall: civil construction Transport Line: new dipole magnet design required, vacuum chamber RF Recirculator End Station

20. Summary CurrentFall 2013Full Capability ERLExternal*ERLExternal*ERLExternal* E (MeV) 80-13580-26080-16580-32080-31080-610 P max (kW) 135012016501203100300 I (mA) 101.25-0.38101.25-0.31103.75-0.5 f bunch (MHz) 7575/750 Q bunch (pC) 13516.7-5135/13.516.7-4/1.67-0.4135-13.550-6.7/5-0.67  transverse (mm-mrad) 10~310/~3~3/~110/~3~5/~2  longitudinal (keV-psec) 50~1550/~15~15/~550/~15~25/~10 75 MHz drive laser; RF drive and gradient limited 750 MHz drive laser; single 100 MV module 12 GeV RF drive; three 100 MV modules (courtesy D. Douglas) *assumes transport line and experimental hall in place