Determination of plasma electron-density distribution from the resonant frequencies of a parallel-plate cavity

A microwave resonant cavity method of plasma diagnostics is demonstrated for a parallel-plate cavity containing a cold, collisionless, and isotropic plasma. The method is extended to more general cavities and plasmas in the Appendix. The approach presented here differs from perturbational formulations in that assumptions about the perturbed fields are not made. The analysis gives an exact relation between the electron-density distribution and the resonant frequencies. Laboratory measurements of resonant frequencies then allow a spatially detailed computation of the electron-density distribution. Results are found to agree well with Langmuir probe measurements.