• A. Lehrach
  FZJ, Jülich
• K. Aulenbacher, A. Jankowiak
  IKP, Mainz
• W. Hillert
  ELSA, Bonn
• C. Montag
  BNL, Upton, Long Island, New York
• T. Weis
  DELTA, Dortmund

The feasibility of a polarized Electron-Nucleon Collider (ENC) with a center-of-mass energy up to 13.5 GeV for luminosities above 2·10³² cm^-2 s^-1 is presently under consideration. The proposed concept integrates the planned 14 GeV High-Energy Storage Ring (HESR) for protons/deuterons and an additional 3 GeV electron ring. Calculations of cooled beam equilibria including intra-beam scattering and beam-beam interaction have been performed utilizing the BetaCool code. A special design of the interaction region is required to realize back-to-back operation of the HESR storage ring together with the elaborated collider mode. For polarized proton/deuteron beams additional equipment has to be implemented in several machines of the acceleration chain and the HESR to preserve the beam’s polarization. A scheme for polarized electrons is still under investigation. In this presentation the required modifications and extensions of the HESR accelerator facility at the future International Facility for Antiproton and Ion Research (FAIR) are discussed and the proposed concept is presented.

• S.A. Martin, R. Gebel, A. Lehrach, B. Lorentz, M. Nekipelov, D. Prasuhn, F. Rathmann, H.-J. Stein, H. Stockhorst, D.M. Welsch
  FZJ, Jülich
• A. Garishvili, A.N. Nass, E. Steffens
  University of Erlangen-Nürnberg, Physikalisches Institut II, Erlangen
• P. Lenisa, M. Statera
  INFN-Ferrara, Ferrara

The PAX Collaboration is planning experiments using polarized Antiprotons. The only experimentally proven method so far which could lead to the production of polarized antiprotons is the spin-filtering. In particular, spin-filtering has been used to generate polarized protons in an experiment at the Heidelberg TSR*. In order to optimize spin-filtering for the production of polarized antiprotons dedicated experiments are planned at COSY with protons and AD (CERN) with antiprotons. The experimentation at COSY has already started in 2007. A decisive experiment has been performed to settle a long controversy about the role of electrons in the polarization buildup by spin-filtering. Instead of studying the polarization buildup in an initially unpolarized beam, the inverse situation was investigated by observation of depolarization of an initially polarized beam. For the first time the electrons of the electron cooler have been used as a target to study their depolarizing effects on the stored beam. At the same time a series of machine experiments have been performed to study the beam lifetime at different energies.

*F. Rathmann et al., Phys. Rev. Lett. 71, 1993, p.1379