Ion cyclotron resonance heating in the Wisconsin levitated octupole

Abstract

Ion cyclotron resonance heating has been investigated, both experimentally and theoretically, on the Wisconsin Levitated Octupole. Heating of both ions and electrons has been observed. Typically, a two component ion energy distribution is produced (300 and 50 eV) with 500 kW of r.f. power coupled into a 5*1012 cm-3 plasma. Power is coupled to the plasma with an antenna that also serves as the inductor of an oscillator tank circuit. The oscillator is tunable from 1 to 3 MHz and can be applied for periods up to 10 ms. The experiments were performed with hydrogen, gun-injected plasmas. Most of the theoretical work presented deals with a calculation that predicts the plasma loading. A slab model is used, and the questions of accessibility, polarization and damping of the evanescent radio frequency electromagnetic fields are addressed. It is found that cold plasma theory cannot account for the heating, and therefore hot plasma theory is invoked to explain the results. The loading measurements and theoretical predictions are found to be in reasonable agreement.