  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.
