Halos of intense proton beams

Beam halo is an important issue for accelerator driven transmutation technologies and other applications of CW proton accelerators. These projects include, for example, the accelerator transmutation of waste, accelerator-based conversion of plutonium, accelerator production of tritium, and the development of a next-generation spallation neutron source. To keep radioactivation within acceptable limits these accelerators must operate with a very low beam loss (less than a nanoampere per meter). Beam loss is associated with the presence of a low density halo far from the beam core. Understanding the physics of halo production and determining methods to control beam halo are important to these projects. In recent years significant advances have been made, both analytically and computationally. In the following we describe recent developments in beam halo theory and simulation, including results from multi-million particle simulations.