Experimental studies of plasma heating due to the parametric decay of alarge-amplitude pump into lower-hybrid waves

Plasma heating of a high-density low-temperature linear plasma by the parametric decay instability of lower-hybrid waves excited in a parallel-plate geometry is studied experimentally for ww/sub lh/ = 3 and 10. The electric-field distribution is modeled considering the higher-order modes produced in this geometry. A method of measuring bulk electron temperature in the presence of an oscillating potential is developed and validated. Electron-heating results show that the parametric decay instability in this geometry is strongly driven and strongly convectively damped, resulting in very rapid electron heating that saturates in a time of 20-30w-1. Bulk electron heating consistent with a recent theory of parametric decay of a large-amplitude driver near the lower-hybrid frequency is also observed. Control of the instability by use of a finite-bandwidth driver is also studied, and results show that the threshold of the parametric decay instability in this geometry can be increased by a factor of 3 by a noise-modulated driver with Δww - .7. These results are contrasted with earlier studies