Current losses and equilibrium in RF linear accelerators

In the conventional design of RF linear accelerators the charged particle bunches are not in thermal equilibrium. With high currents, space charge couples the transverse and longitudinal self forces, leading to emittance growth and halo formation as the beam relaxes toward an equipartitioned state. Particle losses to the walls can occur as a result of halo formation and also through the natural tail on the equilibrium distribution. Particle losses due to either a halo or a tail can cause radioactivity in the conducting channel, inhibiting routine maintenance. The properties of the beam are described in a new design for RF linacs in which the beam is kept in thermal equilibrium, and the current loss rate is found for the tail on the thermal equilibrium distribution.