Microwave Diagnostics in Diffusive and Constricted Medium-Pressure Discharges

The high-frequency (HF) electron current induced in a dc discharge plasma bysuperimposing a HF electric field presents a useful tool for the diagnosticsof the time-dependent electron behavior of the plasma. This response to theHF field has been recently studied in diffusive discharge plasmas at lowergas pressures and discharge currents. These studies are extended tomedium-pressure plasmas operating in the diffusive as well as in theconstricted mode. In particular, the impact of the electron–electroninteraction on the phase delay between the HF field and electron current inconstricted column plasmas has been experimentally and theoreticallyanalyzed. Furthermore, the problem has been studied if, under the conditionsof pronounced electron–electron interaction, the determination of theelectron density will further on be possible by using the phase delay. Themeasurements of the delay have been performed by means of the microwaveresonator method in a medium-pressure krypton glow discharge operating inthe diffusive as well as the strongly constricted mode. In addition, thedelay has been theoretically determined by treating the appropriatetime-dependent electron kinetic equation at high frequencies of thesuperimposed microwave field.