Polarized Electron Source for the ILC

1. Polarized Electron Source for the ILC Axel Brachmann - SLAC - XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

2. Overview • ILC and Electron Source Layout • ILC e- Source Parameters • Reference Design Report • Engineering Design Report • R&D • Source Laser System • Electron Gun • Polarized Photocathodes • Summary XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

3. Current ILC Schematic XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

4. Overall e- Source Layout Schematic XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

5. Tunnel Maze (Source, RTML, Main Linac, Damping Ring, Service, Shafts) XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

6. ILC Source Parameters XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

7. Design Process, History and Future ? 2005 2007 2010 NLC, JLC, TESLA ILC Construction ~ 7 years RDR EDR Funding Decision XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

8. Institutions & International Context • Area Systems Groups • SLAC • JLAB • KEK • Others TBD • Technical Systems Groups and R&D Projects • SLAC, FNAL, JLAB, BNL • University of Wisconsin • KEK, University of Hiroshima • CERN, DESY • Others TBD XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

9. Area Systems (e.g. e- source) Reference Design Reporthttp://www.linearcollider.org/cms/ • Area Systems: • Accelerator physics • technical specifications • Technical Systems: • Magnet System • Vacuum System • Cryogenics • RF system • Dumps & Collimators • Global Systems: • Conventional Facilities • Installation • Instrumentation • Controls Cost Reduction Global Systems Technical Systems XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

10. RDR Cost of Electron Source Overall Total of e- source : ~ 165 M$ ILC total: ~ 6.7 B$ XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

11. Source Integration example:Damping Ring / Source RF System Compatibility DR fundamental RF : 650 MHz DR fill patterns provides clearing gaps for electron and ion clod 1. Pulse 2. Pulse 3. Pulse First Revolution t Bunch spacing is 2 RF buckets Second Revolution mini-train gap (e.g. total of 44 bunches in mini-train, 82 mini-trains) t must be an integer multiple of SHB periods, most critical for SHB I Example: t = 177 DR RF buckets = 272.31 ns  SHB frequency of 216.67 MHz XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

12. Engineering Design Report (FY08-FY10) • Next step after RDR • Conceptual design  Engineered design • Goal is to have a ‘construction ready’ design and submit a construction proposal to funding agencies • Detailed cost analysis • In addition to design and engineering: • Conduct required R&D • Prototype of critical components XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

13. R&D Focus to support the EDR • Source Drive Laser System • Photocathodes • DC Gun • Accelerator Physics • Alternatives beyond the baseline design: (not currently funded by ILC) • Polarized RF gun • e.g. SC polarized RF gun research at BNL (see J. Kewisch’s talk ‘The polarized SCR gun experiment’; this afternoon) Demonstrate ILC beam XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

14. Source Laser Requirements • Central wavelength : ~ 790 nm • Laser pulse energy is determined by cathode QE • ~ 5 μJ mirco pulse energy • Tunability of  20 nm • Pulse shaping requires bandwidth • Availability of high power cw pump source to facilitate amplification at 3 MHz • To tap industrial resources  common lasing medium is required • Choice of Ti:Sapphire laser system pumped by solid state Nd:YAG (or similar) XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

15. Source Laser Schematic XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

16. Gun Development Program • SLC DC gun is baseline design • Optimizion for ILC conditions will improve operation of the source • Emittance • Energy spread • Beam loading • Electrode materials and geometry • HV power supply • HV 140 – 200 kV • Pulsed power supply may be necessary to mitigate beam loading • R&D program starts in FY08 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

17. Comparison of DC Gun Parameters worldwide (compilation courtesy of M. Poelker, JLab) Under construction Proposed operating Historical or diminished scope XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

18. Accelerator Physics Beam envelope along the NC injector • 95% of electrons produce by the DC gun are captured within 6-D damping ring acceptance: (Ax+Ay)0.09m and E x z  (25 MeV) x (3.46 cm) XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

19. Photocathode Status • Baseline design: strained layer supperlattice GaAs/GaAsP • Polarization ~ 85 - 90 % ,QE 1% maximum, 0.3-0.5% routinely High gradient p-doping increases QE and reduces surface charge limit: 5 x 1019 cm-3 5 x 1017 cm-3 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

20. Photocathode R&D program • R&D continues on cleaning and surface preparation techniques (e.g. Atomic Hydrogen Cleaning) • Determine optimum doping level for ILC conditions • Investigate depolarization mechanisms using time resolved Faraday rotation • Alternatives are InAlGaAs/GaAs strained supperlatice photocathodes • 91% polarization has been reported, see talk by Y. Mamaev: ‘Record values of polarization and quantum efficiency for semi-conductor photocathodes’ Friday, 10:10-10:40, Plenary Session XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

21. Summary • Reference Design  Conceptual Design  • Engineering Design  Construction Proposal in progress • R&D topics: • Source Laser System • Electron Gun • Photocathodes • International collaboration • broad range of expertise can be tapped • Logistics of collaboration are challenging • Funding in different regions determine pace of progress XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)

22. Contributors J. Clendenin, T. Maruyama, F. Zhou, J. Sheppard, K. Ioakeimidi, R. Prepost, M. Poelker, M. Kuriki, Many more, see RDR author list. XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL)