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

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 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:

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Nominal Source Parameters ParameterSymbolValueUnits Bunch PopulationNbNb 2x10 10 # Bunches per pulsenbnb 2625# Bunch spacingtbtb 369ns Pulse repetition ratef rep 5Hz Injection Energy (DR)E0E0 5GeV Beam Power (x1.5)PoPo 300kW Polarization e-(e+)P80(30)%

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Positron Source Layout (undulator based scheme)

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Winding undulator on a custom built winding machine Undulator winding (RAL/UK) Courtesy Jim Clarke of CCRL/Daresbury

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 Right now the cold mass has diameter 1.5 inch. Designed cold mass with1 inch diameter 6 Fabricated undulator with 6.35 mm Inner diameter (1/4”) available for the beam; 13.5 mm period  K=1.48 measured 1 in Alexander Mikhailichenko/Cornell

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 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

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Cockroft institute prototype experiment simulation Technical drawing provided by I.Bailey Simulation, Induced field, z-component, 2000RPM z0z0 D – 1m, rim width – 30mm, rim thickness – 14mm, distance between magnet poles is 5cm, field – 1.5Tesla

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Photon Number Spectrum Number of photons per e- per 1m undulator: Old BCD: UK1: 1.946; UK2: 1.556; UK3: Cornell1: 0.521; Cornell2: 1.2; Cornell3: 0.386

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Initial Polarization of Positron beam at Target exit(K=0.92 u=1.15)

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Initial Pol. Vs Energy of Captured Positron Beam

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Yield contribution from different harmonics – new baseline undulator, without collimator High order harmonics are important

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Comparison of positron yield from different undulators High K DevicesLow K Devices BCDUK IUK IIUK IIICornell ICornell IICornell III Period (mm) K Field on Axis (T) Beam aperture (mm)Not Defined First Harmonic Energy (MeV) Yield(Low Pol, 10m drift)~2.4~1.37~1.12~0.86~0.39~0.75~0.54 Yield(Low Pol, 500m drift) ~2.13~1.28~1.08~0.83~0.39~0.7~0.54 Yield(Pol)~1.1~0.7~0.66~0.53~0.32~0.49~0.44 Target: 1.42cm thick Titanium

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 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.

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 SLC OMD was a pulsed flux concentrator It is a large extrapolation from SLC to ILC –1  s -> 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.

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 ¼ wave solenoid seems more feasible 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? ANL ¼ wave solenoid simulations W. Liu

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 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 P.G. Hurh & Z. Tang A. Mikhailichenko Alexander Mihkailchenko, Cornell Univ.

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 Capture Efficiency: FZ, YN SLAC; WL ANL Sheppard, SLAC

CCAST ILC Meeting, IHEP, Beijing, Nov 5-7, 2007 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?