Measurement of Spatial Distribution of Electron Density in a Plasma by Microwave Free Space Method

A measurement of the spatial distribution of the electron density in a plasma was carried out. The method used here for the measurement was analogous to Wharton's method on the use of interferometer, but the difference existed in the measurement of electron density of the plasma axis. In the present experiment, the latter was determined by the microwave radiation from the plasma. This procedure was applicable for the plasma column whose diameter was comparable with a wavelength. The plasma studied here was a positive column, whose diameter was about 8 cm long, in helium at pressure of 0.7 mmHg. Microwave interferometer was used in K-band and the receiver for microwave radiation in X-band. Experimental results obtained by microwave method were compared with those by Langmuir probe method, and a satisfactory agreement between two results was obtained.