• J. Gronberg, B. Stuart
  LLNL, Livermore, California
• A. Seryi
  SLAC, Menlo Park, California

The realization of a photon collider option at a future TeV scale electron linear collider requires the generation of high average power picosecond laser pulses. Recirculating cavities have been proposed to reduce the amount of laser power that needs to be generated, however, these cavities impose stringent limits on the wavefront quality and stability of the laser architecture. We report on a design study of a high average power laser amplifier architecture which can produce the required laser time structure and stability to drive these recirculating cavities.

• I.R. Bailey, J.A. Clarke, D.J. Scott
  Cockcroft Institute, Warrington, Cheshire
• I.R. Bailey
  Lancaster University, Lancaster
• C.G. Brown, J. Gronberg, L.B. Hagler, W.T. Piggott
  LLNL, Livermore, California
• L.J. Jenner
  Imperial College of Science and Technology, Department of Physics, London
• L. Zang
  The University of Liverpool, Liverpool

The efficiency of future positron sources for the next generation of high-energy particle colliders (e.g. ILC, CLIC, LHeC) can be improved if the positron-production target is immersed in the magnetic field of adjacent capture optics. If the target is also rotating due to heat deposition considerations then eddy currents may be induced and lead to additional heating and stresses. In this paper we present data from a rotating target wheel prototype for the baseline ILC positron source. The wheel has been operated at revolution rates up to 1800rpm in fields of the order of 1 Tesla. Comparisons are made between torque data obtained from a transducer on the target drive shaft and the results of finite-element simulations. Rotordynamics issues are presented and future experiments on other aspects of the positron source target station are considered.

• J. Gronberg, A. Abbott, C.G. Brown, J.B. Javedani, W.T. Piggott
  LLNL, Livermore, California
• J.A. Clarke
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire

The positron source at a future TeV scale electron linear collider will need to generate positrons at a rate two orders of magnitude larger than have been previously achieved. We report on a design of a 3.5 Tesla pulsed flux concentrator magnet which uses liquid nitrogen cooling of the flux concentrator plates to reduce the electrical resistance leading to reduced energy deposition and the ability to generate the required 1 ms pulse duration. This magnet can double the collection efficiency of positrons emitted from the target.