• G. Stancari, A.I. Drozhdin, G.F. Kuznetsov, V.D. Shiltsev, D.A. Still, A. Valishev, L.G. Vorobiev
  Fermilab, Batavia
• R.W. Assmann
  CERN, Geneva
• A.A. Kabantsev
  UCSD, La Jolla, California
• G. Stancari
  INFN-Ferrara, Ferrara

Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and built. Its performance and stability were measured at the Fermilab test stand. The gun will be installed in one of the existing Tevatron electron lenses for preliminary tests of the hollow-beam collimator concept, addressing critical issues such as alignment and instabilities of the overlapping proton and electron beams.

• A. Valishev, G.F. Kuznetsov, V.D. Shiltsev, G. Stancari, X. Zhang
  Fermilab, Batavia
• A.L. Romanov
  BINP SB RAS, Novosibirsk

Tevatron electron lenses have been successfully used to mitigate bunch-to-bunch differences caused by long-range beam-beam interactions. For this purpose the electron beam with uniform transverse density distribution was used. Another planned application of the electron lens is the suppression of tune spread due to head-on beam-beam collisions. For this purpose, the transverse distribution of e-beam must be matched to that of the antiproton beam. In 2009, the gaussian profile electron gun was installed in one of the Tevatron electron lenses. We report on the first experiments with non-linear beam-beam compensation. Discussed topics include measurement and control of the betatron tune spread, importance of the beam alignment and stability, and effect of the electron lens on the proton and antiproton beam lifetime.