Undulator Based ILC Positron Source Studies

1. Undulator Based ILC Positron Source Studies Wei Gai Argonne National Laboratory CCAST ILC Accelerator Workshop Beijing, Nov 5 – 7, 2007

2. Acknowledgement: The reported works are produced by the ILC positron collaborations: SLAC, LLNL, ANL, ORNL, BNL, KEK, RAL, Daresbury/Cockcroft, DESY and others. Most Recent Summaries can be found at: www.hep.anl.gov/ILC-positron/

3. Nominal Source Parameters

4. Positron Source Layout (undulator based scheme)

5. Undulator winding (RAL/UK) Winding undulator on a custom built winding machine Courtesy Jim Clarke of CCRL/Daresbury

6. New tapering tested: conical transition from Iron to brass helix yoke New original technology of wire return tested New iron spacing technology New winding machine Alexander Mikhailichenko/Cornell 1 in Fabricated undulator with 6.35 mm Inner diameter (1/4”) available for the beam; 13.5 mm period  K=1.48 measured Right now the cold mass has diameter 1.5 inch. Designed cold mass with1 inch diameter 6

7. Target • Target • 100 m/s rim speed • 1-m diameter wheel • 1.4 cm • Ti-96%Al-4%V • 8% heat deposition • Stress from motion , stress from heating • Vacuum seals that allow water flow and rotation • Magnetic fields & moving metal

8. Cockroft institute prototype experiment simulation Technical drawing provided by I.Bailey z0 Simulation, Induced field, z-component, 2000RPM D – 1m, rim width – 30mm, rim thickness – 14mm, distance between magnet poles is 5cm, field – 1.5Tesla

9. Photon Number Spectrum Number of photons per e- per 1m undulator: Old BCD: 2.578 UK1: 1.946; UK2: 1.556; UK3: 1.107 Cornell1: 0.521; Cornell2: 1.2; Cornell3: 0.386

10. Initial Polarization of Positron beam at Target exit(K=0.92 lu=1.15)

11. Initial Pol. Vs Energy of Captured Positron Beam

12. Yield contribution from different harmonics – new baseline undulator, without collimator High order harmonics are important

13. Comparison of positron yield from different undulators Target: 1.42cm thick Titanium

14. Immersed target works well in simulation, but can we use it? • Difficulties: Conventional magnets, ~ MW power supply. • Rotating in the magnetic field, people use this scheme for breaks. What else we can do? • Build pulsed magnet; • Lithium Lens(?) • Use ¼ wave transformer scheme.

15. SLC OMD was a pulsed flux concentrator • It is a large extrapolation from SLC to ILC • 1ms -> 1ms pulse width • Previous magnet for hyperon experiment was the closest thing we could find. • Cryogenic nitrogen cooling of the concentrator plates. • ANL and LLNL did initial rough electromagnetic simulations. Not impossible but an engineering challenge. • No real engineering done so far.

16. ¼ wave solenoid seems more feasible ANL ¼ wave solenoid simulations • Capture efficiency is only 25% less than flux concentrator • Low field at the target reduces eddy currents • This is probably easier to engineer than flux concentrator • SC, NC or pulsed NC? W. Liu

17. Alexander Mihkailchenko, Cornell Univ. Lithium lens • Lithium Lens • Will lithium cavitate under pulsed heating? • window erosion • Will lithium flow adequately cool the windows? • Lens is defocusing for electrons • Increased heating and radiation load in the capture section A. Mikhailichenko P.G. Hurh & Z. Tang

18. Capture Efficiency: FZ, YN SLAC; WL ANL Sheppard, SLAC

19. Summary • Systematic studies of the ILC positron source performed. Various issues addressed. • Basic-Basic (1/4 wave) scheme may work, but require 300 m long undulator and 3 GeV Linac to compensate the energy loss. • Challenges and further works: • Target design: Mechanical and materials. (Ti, W, Eddy current and radiation damages). • Capturing Magnets (Lens): Small R&D investments may yield huge savings. • Target Hall: Remote handling target and other beamline components. • Undulator: electron beam jitter tracking through the undulator, polarizations, and other errors like undulator and alignments. • Electron beam properties after traversing the undulator, anything changes except energy?