Plasma Electron Density Distribution from Cavity Frequency Shift Data

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Abstract
The square of the plasma frequency of electrons in a plasma contained in a cylindrical cavity resonator can under some circumstances be adequately represented by the two-parameter function Π2=Π02(1+ρ)(1−r2/a2)ρ.To determine the nonuniformity parameter ρ and the average plasma frequency Π0 it is necessary to measure the frequency shifts of two modes. The TMLMO modes have suitable properties for this purpose, and in addition they are unaffected by axial magnetization of the plasma. Calculations, based on a variational approximation, are presented in the form of a mapping of the parameter space of ρ and Π02 onto the frequency space of the TM010 and TM110 resonant shifts. With a trivial modification the results apply equally to the TM010 and TE011 modes. The range of parameters is 0–6 for ρ and 0−76 for (aΠ0/cj01)2. The results show the feasibility of inferring gross characteristics of the distribution from two frequency measurements having an accuracy of 1 part in 103.