RF Breakdown in Magnetic Fields: Previous Work, Recent Theory, and Future Plans

Recent experiments on the breakdown of rf cavities revealed severe surface damage and a reduction of the maximum accelerating gradient after operation in an external magnetic field. This finding implies the possibility of serious problems for cooling lattices wherein rf cavities and external magnetic fields coexist, such as those of the proposed neutrino factory and muon collider. An experimental program that could study those problems and their possible solutions is discussed. Emphasis is given to a magnetically insulated cavity design in which the walls are parallel to the magnetic field lines and consequently damage from field emission is expected to be suppressed.