Breakdown in RF Cavities

We present a simple model of breakdown in rf cavities. For most events this involves tensile stress and tensile strength, however other effects can also contribute. We discuss the effects of different materials, fatigue, high pressure gas, primary and secondary emission sites, local field enhancements, dark currents, secondary emission, work functions, magnetic fields, macro and microscopic fracture mechanisms high current densities, surface and subsurface defects, and astronomical power densities. While primarily devoted to normal conductors, this work also has consequences for superconducting rf surfaces.