Collimation with hollow electron beams is a technique for halo control in
high-power hadron beams. It is based on an electron beam (possibly pulsed or
modulated in intensity) guided by strong axial magnetic fields which overlaps
with the circulating beam in a short section of the ring. The concept was
tested experimentally at the Fermilab Tevatron collider using a hollow electron
gun installed in one of the Tevatron electron lenses. Within the US LHC
Accelerator Research Program (LARP) and the European FP7 HiLumi LHC Design
Study, we are proposing a conceptual design for applying this technique to the
Large Hadron Collider at CERN. A prototype hollow electron gun for the LHC was
built and tested. The expected performance of the hollow electron beam
collimator was based on Tevatron experiments and on numerical tracking
simulations. Halo removal rates and enhancements of halo diffusivity were
estimated as a function of beam and lattice parameters. Proton beam core
lifetimes and emittance growth rates were checked to ensure that undesired
effects were suppressed. Hardware specifications were based on the Tevatron
devices and on preliminary engineering integration studies in the LHC machine.
Required resources and a possible timeline were also outlined, together with a
brief discussion of alternative halo-removal schemes and of other possible uses
of electron lenses to improve the performance of the LHC.Comment: 24 pages, 1 table, 10 figure