RF power loss, local electric and magnetic field enhancement due to surface roughness

Surface roughness plays an important role in a cavity or slow wave structure. It may cause enhanced RF power absorption. It may lead to excessive local electric field enhancement that triggers RF breakdown. In a superconducting cavity, surface roughness may also cause local magnetic field enhancement that leads to abrupt quenching, i.e., rapid loss of superconductivity. In this work, we analytically compute the power absorption due to a hemispherical protrusion on a resonant cavity´s surface. The local field enhancement factors of both electric field and magnetic field on the protrusion are also calculated analytically. This protrusion may represent a foreign object since its permittivity ??, permeability ?? and conductivity ?? may take on arbitrary values. Scaling laws are derived.