Electron cyclotron resonance heating and confinement in the W VII-A stellarator

Plasma generation and heating of OH-current free plasmas by strong ECR-wave irradiation were studied on the Garching W VII-A stellarator for three kinds of wave launching: direct irradiation of the gyrotron modes (mainly TE02 mode corresponding to a 50% O-mode and 50% X-mode mixture) from the low field side, and advanced wave launching (linearly polarized TE11 and HE11 mode) in O-mode orientation (E//Bo, Bo, k perpendicular to Bo). The nonabsorbed fraction was reflected into the plasma in the X-mode (E perpendicular to Bo) by a focusing polarization twist reflector mounted to the inner torus wall. The experiments were performed at 28 GHz (1 Tesla resonance B-field) with 200 kW RF power and a pulse duration of