1. Spin Tracking at the ILC Positron Source with PPS-Sim POSIPOL’11 V.Kovalenko POSIPOL’11 V. Kovalenko 1, G. Moortgat-Pick 1, S. Riemann 2, A. Ushakov 1 1 University of Hamburg/DESY 2 DESY, Zeuthen

2. Components of Positron Source Primary Beam Undulator photons Target Solid wheel (Ti-alloy) Optical Matching Device and Accelerating Cavity Quarter-wave transformer 1.3 GHz cavity embedded into solenoid Acceptance of Damping ring 1% energy spread, ε x +ε y = 0.09 rad m Photon Collimator (optionally) V.Kovalenko POSIPOL’11 RF Cavity Target Photons

3. Undulator: k=0.92, λ u =11.5 mm Length of undulator: 231 m Target to middle of undulator: 500 m Target: 0.4X 0, Ti6Al4V Target thickness: 14 mm Drive beam energy: 100 GeV to 250 GeV (end of linac) Maximal magnetic field on the axis of QWT: 1T to 2T QUARTER-WAVE CAPTURING V.Kovalenko POSIPOL’11 Low field, 1.0 Tesla on axis, tapers down to 1/2 T. Initial strong solenoid magnet with bucking to cancel B field on target The target will be rotating in a B field of about 0.2T

4. Max Field Drive beam energy, GeV 1.0 T100150200250 Captured yield 0.21821.15262.50943.7475 Polarization0.34060.32120.27760.2433 1.5 T 100150200250 Captured yield 0.17251.13242.70754.3452 Polarization0.35010.32480.29280.2673 2.0 T 100150200250 Captured yield 0.20571.21873.08054.9702 Polarization0.35810.33700.30540.2568 DRIVE BEAM ENERGY DEPENDENTS (no collimation) Yield is calculated as Ne+ captured/Ne- in drive beam V.Kovalenko POSIPOL’11

5. Collimator radius, mm Captured YieldPolarization 1.0 T1.5 T2.0 T1.0 T1.5 T2.0 T 0.50.630.720.710.650.720.69 0.751.271.461.570.610.660.64 11.902.212.500.550.580.57 1.252.452.893.340.480.510.50 1.52.863.363.920.410.440.42 1.753.173.814.380.350.37 23.354.024.640.310.340.31 2.253.504.184.810.280.300.29 2.53.654.274.900.250.280.27 2.753.644.294.940.240.27 33.684.314.920.240.270.26 43.684.345.010.230.270.25 53.704.325.040.230.270.25 V.Kovalenko POSIPOL’11 Polarization depends on collimator radius for 250 GeV drive beam energy

6. Drive beam energy ~ 250GeV K=0.92 λ=11.5 mm No collimation Distance between undulator center and QWT ~ 500 m Undulator length ~ 231 m Phase of RF field is optimized for yield Length of QWT ~ 130 mm Maximal magnetic field ~ 1 T Distance to target ~ 150 mm Possible polarization ~ 28% Yield ~ 3 e + /e - Polarization and yield vs distance from QWT to target V.Kovalenko POSIPOL’11

7. After applying collimator with 2 mm radius: Polarization enhancement of ~ 6 – 7% Yield still fulfils requirement 1.5 e + /e - Polarization and yield vs distance from QWT to target 2 mm collimator radius V.Kovalenko POSIPOL’11

8. Polarization and yield vs length of QWT (no collimation) Longer QWT gives a higher value of polarization "Captured" Yield(e + /e - ) V.Kovalenko POSIPOL’11

9. phase change of RF field makes it possible to increase positron polarization up to ; the higher polarization is the lower yield is. phase change of RF field makes it possible to increase positron polarization up to ~ 31%; the higher polarization is the lower yield is. ~ 140° RF field ~ 31% e + polarization ~ 1.5 e + /e - V.Kovalenko POSIPOL’11 250 GeV drive beam vs phase of RF field

10. For 250 GeV energy beam and without collimation polarization lies in a range of 24-26%. This value of polarization is too small to achieve full physics potential of polarized beams. Increasing distance between target and QWT gives an enhancement of polarization. Collimator with 2 mm aperture radius increases the polarization up to 35% and yield still fulfils requirement 1.5 e + /e - for the source at 250 GeV Longer QWT gives a higher value of polarization. Summary V.Kovalenko POSIPOL’11

11. Data file with realistic positron distribution in the 6-D phase space taken from PPS-Sim will be used as input file for BMAD. Spin tracking up to DR in PPS-Sim + Bmad is required. Plans V.Kovalenko POSIPOL’11