Application of rf superconductors to linacs for high-brightness proton beams

A series of superconducting structures for the acceleration of high-current ion beams is being developed, and two prototype Nb cavities are under construction. These cavities operate in a frequency-velocity range which, for superconducting structures, has been little explored: frequencies of 0.4 GHz to more than 1 GHz, and velocities of 0.1c to 0.5c. Issues discussed include: need for strong beam loading (∝104), need for strong focusing elements located close to the cavities, minimization of beam impingement and beam instabilities. (orig.)