Microwave Plasma Density Measurements

Abstract

To make plasma density measurements on a cylindrical column with a microwave cavity requires a precise curve of cavity frequency versus density. In practice, one uses the measured cavity frequency (without a plasma) and the initial slope of this curve. An analysis is made for the TM₀₁₀ mode to determine the effects of nonuniformity (a parabolic density) and of the holes in the cavity where the plasma column is admitted. It is shown that both effects result in a smaller slope so that one underestimates the density if they are not taken into account.