• F. Zimmermann, Y. Papaphilippou, L. Rinolfi, A. Vivoli
  CERN, Geneva
• F. Antoniou
  National Technical University of Athens, Zografou
• R. Chehab
  IN2P3 IPNL, Villeurbanne
• M. Kuriki
  HU/AdSM, Higashi-Hiroshima
• T. Omori, J. Urakawa
  KEK, Ibaraki
• A. Variola
  LAL, Orsay
• V. Yakimenko
  BNL, Upton, Long Island, New York

The Compton positron source of a future linear collider must obtain the target bunch population by accumulating a large number of positron packets, arriving either in a number of bursts from a “Compton ring”, with intermediate damping of the scattering electron beam, or quasi-continually from a “Compton energy recovery linac”. We present simulation results for the longitudinal stacking of Compton positrons in the ILC damping ring and the CLIC pre-damping ring, reporting parameter optimization, stacking efficiency, possible further improvements, and outstanding questions.

• A. Variola, C. Bruni, I. Chaikovska, O. Dadoun
  LAL, Orsay
• R. Chehab
  IN2P3 IPNL, Villeurbanne
• M. Kuriki
  HU/AdSM, Higashi-Hiroshima
• T. Omori, J. Urakawa
  KEK, Ibaraki
• L. Rinolfi, A. Vivoli, F. Zimmermann
  CERN, Geneva

One of the main challenges for the future linear colliders projects (ILC and CLIC) is to design an efficient positron source taking into account the constraints imposed by the target heating. At present, different schemes have been analysed to produce high energy gammas and to convert them in an amorphous target. One of them considers the possibility to boost the energy of the backscattered photons of a laser pulse by Compton effect. This method is very attractive since the source is independent from the main Linac and since the photon helicity is conserved in Compton scattering and subsequently transferred to the produced pairs. This allows the physics experiments disposing of both positron and electron polarised sources. Different schemes have been proposed to provide the electron beam for the Compton collisions. taking into account the constraint imposed by the low value of the Thomson cross section. One of the explored possibilities is to design an ERL with relatively low repetition frequency, high charge per pulse and then to stack the produced positrons in an accumulation ring. Different considerations on this scheme will be illustrated and the main constraints discussed.

• L. Rinolfi, F. Antoniou, H.-H. Braun, Y. Papaphilippou, D. Schulte, A. Vivoli, F. Zimmermann
  CERN, Geneva
• E.V. Bulyak, P. Gladkikh
  NSC/KIPT, Kharkov
• R. Chehab
  IN2P3 IPNL, Villeurbanne
• J.A. Clarke
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• O. Dadoun, P. Lepercq, R. Roux, A. Variola, Z.F. Zomer
  LAL, Orsay
• W. Gai, W. Liu
  ANL, Argonne
• T. Kamitani, T. Omori, J. Urakawa
  KEK, Ibaraki
• M. Kuriki
  HU/AdSM, Higashi-Hiroshima
• I. Pogorelsky, V. Yakimenko
  BNL, Upton, Long Island, New York
• T. Takahashi
  Hiroshima University, Graduate School of Science, Higashi-Hiroshima

The CLIC polarized positron source is based on a positron production scheme in which polarized photons are produced by Compton process. Compton backscattering happens in a so-called "Compton ring" where an electron beam of 1.06 GeV interacts with a powerful laser beam amplified in an optical resonator. The circularly-polarized gamma rays are sent on to a target, producing pairs of longitudinally polarized electrons and positrons. An Adiabatic Matching Device maximizes the capture of the positrons. A normal-conducting 2 GHz Linac accelerates the beam up to 2.424 GeV before injection into the Pre-Damping Ring (PDR). The nominal CLIC bunch population is 4.4x10⁹ particles per bunch. Since the photon flux coming out from a "Compton ring" is not sufficient to obtain the requested charge, a stacking process is required in the PDR. Another option is to use a "Compton Energy Recovery Linac" where a quasi-continual stacking in the PDR could be achieved. A third option is to use a "Compton Linac" which would not require stacking. We describe the overall scheme as well as advantages and constraints of the three different options.