rf-probe method for measurements of electron densities in plasmas at high neutral densities

A radio frequency (rf) method has been developed for measurements of the electron density in weakly ionized gases at high (approx.atmospheric) neutral density. The technique relies on passing an rf current ( f = 15 MHz) between two concentric cylindrical electrodes and relating the measured electrical conductivity to the electron density. The physical principles of the technique and quantitative theory are presented in detail. Test measurements in photoionized helium gas mixtures indicate that the method performs well in the electron density range from about 105 to 1010 cm-3 and that it may also be applicable for measurements of ion densities in plasmas composed predominantly of positive and negative ions