The stabilization and spectroscopic study of microwave generated resonant cavity plasmas

Efficiency measurements of a free-floating resonant cavity plasma system are presented. Temperature measurements 200 mm downstream of the plasma indicate that both the thermal and total efficiencies increase linearly with mass flow rate. Thermal efficiencies of 36.6% and total efficiencies of 25.2% have been measured at the maximum mass flow rate of the experimental system. Bluff-body and swirling flows have been investigated as a means of locating the plasma in a stable, axial position during operation at higher powers, where a positional instability has been observed. Preliminary results indicate that bluff-body stabilization is a promising scheme for microwave plasmas. A high spectral resolution spectroscopic system is presented, which will allow measurement of both plasma temperature and gas exhaust velocity without the assumption of local thermodynamic equilibrium or the need for intensity or wavelength calibration.