Direct observation of electron-Bernstein wave heating by O-X-B-mode conversion at low magnetic field in the WEGA stellarator.

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 (approximately 50 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.