ELECTRON-DENSITY AND COLLISION FREQUENCY OF MICROWAVE-RESONANT-CAVITY-PRODUCED DISCHARGES

A review of perturbation diagnostics applied to microwave resonant cav ity discharges is presented. The classical microwave perturbation tech nique examines the shift in the resonant frequency and cavity quality factor of the resonant cavity caused by low-electron density discharge s. However, the modifications presented allow the analysis to be appli ed to discharges with electron densities beyond the limit predicted by perturbation theory. An ''exact'' perturbation analysis is presented which models the discharge as a separate dielectric, thereby removing the restrictions on electron density imposed by the classical techniqu e. The ''exact'' method also uses measurements of the shifts in the re sonant conditions of the cavity. Third, an electromagnetic analysis is presented which uses a characteristic equation, based upon Maxwell's laws, and predicts the discharge conductivity based upon measurements of a complex axial wave number. By allowing the axial wave number of t he electromagnetic fields to be complex, the fields are experimentally and theoretically shown to be spatially attenuated. The diagnostics a re applied to continuous-wave microwave (2.45 GHz) discharges produced in an Asmussen resonant cavity. Double Langmuir probes, placed direct ly in the discharge at the point where the radial electric field is ze ro, act as a comparison with the analytic diagnostics. Microwave power s ranging from 30 to 100 W produce helium and nitrogen discharges with pressures ranging from 0.5 to 6 Torr. Analysis of the data predicts e lectron temperatures from 5 to 20 eV, electron densities from 10(11) t o 3 X 10(12) cm-3, and collision frequencies from 10(9) to 10(11) s-1.