Improved Microwave Reflection Measurement of Plasmas Produced by Shock Waves.

Abstract

A microwave reflection probe is applied to the measurement of very high electron densities and collision frequencies in plasmas produced by shock waves. The electron density and collision frequency are calculated from a complex reflection coefficient at the sharp boundary of the plasma which exists at the end of the electromagnetically-driven shock tube.Electron densities from 1×1016 to 6×1011cm-3. and electron collision frequencies of the order of 1010 sec-1. which are unsuccessful to be determined in the previous report are here measured by an X-band (9000MC) microwave reflection probe for a decaying plasma which follows that produced by a shock wave reflected at the tube end. The Mach number of the shock Wave is-15 in Argon at an initial pressure of 0.3mm Hg.In addition, the electron temperature is estiluated from the measured electron density and collision frequency, using the electron temperature dependence on the electron-ion collision frequency.It is found that the temperature of electrons in the afterglow plasma which continues after a shock wave is sustained for a relatively long. time. This is a seine tendency of a slow temperature decrease, which is estimated from the temperature dependence on the recombination coefficient as described in the previous report.