Feasibility of Microwave Transmissivity Measurement to Obtain Density Profile of Sheet Plasmas

Abstract

Measurement of microwave transmissivity is a very simple diagnostic method to obtain maximum density and profile information of sheet plasmas. In this method, transmissivity of the incident microwave is measured as a function of probing frequency. When a cutoff exists in the plasma, the main part of the incident wave is reflected, but a part can penetrate the plasma due to the tunnel effect. Transmissivity represents the degree of this effect, and its frequency dependence yields information on the density profile. The feasibility of this method is studied analytically using the Wentzel-Kramers-Brillouin (WKB) method, and the results are compared with those from the numerical solutions of the one-dimensional wave equation. It is shown that the method is useful when the sheet plasma is not too thick. In addition, slight homogeneity along the sheet is required to avoid the effect of refraction.