  A novel concept of controlled halo removal for intense high-energy beams in
storage rings and colliders is presented. It is based on the interaction of the
circulating beam with a 5-keV, magnetically confined, pulsed hollow electron
beam in a 2-m-long section of the ring. The electrons enclose the circulating
beam, kicking halo particles transversely and leaving the beam core
unperturbed. By acting as a tunable diffusion enhancer and not as a hard
aperture limitation, the hollow electron beam collimator extends conventional
collimation systems beyond the intensity limits imposed by tolerable losses.
The concept was tested experimentally at the Fermilab Tevatron
proton-antiproton collider. The first results on the collimation of 980-GeV
antiprotons are presented.
