AN EXPERIMENTAL INVESTIGATION OF SURFACE IONIZED ALKALI AND ALKALINE EARTH PLASMAS CONFINED BY AN INCANDESCENT X-BAND MICROWAVE CAVITY

A homogeneous and near thermal equilibrium plasma device with optical and microwave diagnostics has been designed and constructed. The surface ionized plasma is confined by an incandescent x-band microwave cavity. The cylindrical cavity is supported by two refractory metal waveguides, and is heated by radiation from two larger ohmically heated W cylinders concentric with the cylindrical cavity. The microwave resonant frequencies of the cavity are shifted by the plasma. These shifts have been measured and are used for a very accurate plasma density measurement. The feasibility of using laser induced fluorescene for a direct and localized plasma ion density measurement have been demonstrated using a cw dye laser beam and a Ba('+) plasma. Using K and Cs plasmas, the microwaves have been used at low power ((TURN)1 mW) to detect low frequency oscillations(< 100 kHz) in the cavity. The nature of these oscillations is not certain, but some possibilities are discussed. At high microwave power, low frequency ion accoustic oscillations have been observed in the cavity. There is evidence that these result from the parametric decay of the microwaves. The microwave resonant frequencies of the plasma filled cavity shift as the microwave power is increased due to the ponderomotive force rearranging the plasma. These shifts have been measured as a function of microwave power, and compared to a calculation in which the modified electric field in the cavity is calculated in a self-consistent manner.