• 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.