Direct Observation of Electron-Bernstein Wave Heating byO−X−B-Mode Conversion at Low Magnetic Field in the WEGA Stellarator

Abstract

The ordinary-extraordinary-Bernstein-mode conversion process for overdense plasma heating with electron-Bernstein waves is demonstrated in the WEGA stellarator at low magnetic field ($\sim 50\mathrm{mT}$) at 2.45 GHz. For the first time the conversion from an $O$ wave to an $X$ wave is clearly demonstrated by probe measurements of amplitude and phase of the wave field in the conversion region and supported by two-dimensional full-wave calculations. The propagation and resonant absorption of the Bernstein wave is measured in fast power modulation experiments.