September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 1 Polarized Electron Source for the ILC Axel Brachmann - SLAC -

September 10-14, 2007 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

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 3 Current ILC Schematic

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 4 Overall e- Source Layout Schematic

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 5 Tunnel Maze (Source, RTML, Main Linac, Damping Ring, Service, Shafts)

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 6 ILC Source Parameters ParameterSymbolValueUnit Electrons per bunch (at gun exit)nene 3 x Number Electrons per bunch (at DR injection)nene 2 x Number Number of bunchesNeNe ~ 3000Number Bunch repetition rateFμbFμb 3MHz Bunch train repetition rateF mb 5Hz Bunch length at source tt ~ 1ns Current in bunch at sourceI avg 3.2A Energy stabilityS< 5% rms PolarizationPePe 80 (min)% Photocathode quantum efficiencyQE0.5% Drive laser wavelength 790  20 nm Single bunch laser energyE5μJμJ

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 7 Design Process, History and Future NLC, JLC, TESLA RDR EDR Funding Decision Construction ~ 7 years ILC ?

September 10-14, 2007 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

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 9 Global Systems: Conventional Facilities Installation Instrumentation Controls Reference Design Report Area Systems (e.g. e- source) Technical Systems Global Systems Technical Systems: Magnet System Vacuum System Cryogenics RF system Dumps & Collimators Cost Reduction Area Systems: Accelerator physics technical specifications

September 10-14, 2007 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$

September 10-14, 2007 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 mini-traingap (e.g. total of 44 bunches in mini-train, 82 mini-trains) 3. Pulse1. Pulse2. Pulse tt  t must be an integer multiple of SHB periods, most critical for SHB I Example:  t = 177 DR RF buckets = ns  SHB frequency of MHz Bunch spacing is 2 RF buckets First Revolution Second Revolution

September 10-14, 2007 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

September 10-14, 2007 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

September 10-14, 2007 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)

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 15 Source Laser Schematic

September 10-14, 2007 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

September 10-14, 2007 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) FacilityBeam StructureHV [kV]Avg. CurrentBunch ChargePolarization Bonn – ELSA50 Hz505 μA100 nC / 1 μs+ CEBAFcw: 1497 MHz μA0.13 pC+ Mainz Microtroncw: 2450 MHz10050 μA0.02 pC+ MIT Bates600 Hz, DF=1.5%60120 μA250 nC (25 μs)+ (bulk GaAs) Nagoya/JLC200+ NIKHEV2μs 1 Hz μA SLAC–fixed Target0.3μs 120 Hz120+ SLAC – SLC2ns 120 Hz1202 μA16 nC+ Heidelberg TSRDC<11 mAN/A- JLAB FELcw: 75 MHz35010 mA135 pC- Daresbury ERLPcw: 75 MHz350- Cornellcw: 1300 MHz mA77 pC- JAEA25050 mA- JLab 100kW FELcw: 750 MHz mA135 pC- ILC1ms 3 MHz (1ns) 5Hz ~100 μA5 nC+ EIC – ELIC>1001 mA+ EIC - eRHICcw>10025 mA+ Historical or diminished scope Under constructionProposedoperating

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 18 Accelerator Physics  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) Beam envelope along the NC injector

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 19 Photocathode Status Baseline design: strained layer supperlattice GaAs/GaAsP Polarization ~ %,QE 1% maximum, % routinely High gradient p-doping increases QE and reduces surface charge limit: 5 x cm -3  5 x cm -3

September 10-14, 2007 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

September 10-14, 2007 XIIth International Workshop on Polarized Sources, Targets & Polarimetry, Brookhaven National Laboratory (BNL) 21 Summary Reference Design  Conceptual Design  Engineering Design  Construction Proposalin 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

September 10-14, 2007 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.