Resistive flux saving and current profile control during lower hybrid waves assisted current rise in TORE SUPRA

TORE SUPRA has been designed to study long pulse operation for times longer than the time required to reach equilibrium conditions in the plasma-wall interaction. The available flux swing is limited to 15 Wb then the plateau duration is about 12 s in typical 1.3 MA ohmic discharges. This time has been extended to 35 seconds by applying Lower Hybrid (LH) waves during the flat top and the current rise. Taking into account the minimum flux consumed to rise the current, about half of the plasma surface flux is consumed in compensating the resistive losses during the current ramp. So far as the current ramp is performed at low density in the presence of an electric field, LH current drive is an attractive method to reduce the flux consumption during the current rise phase. The flux saving and current profile control experiments described in this paper have been carried out with the assistance of the ohmic primary circuit at a line averaged electron density varying typically from ne=1x1019 m-3 to ne=2x1019 m-3 at various current ramp-up rates, various LH power levels and various parallel wavenumbers. Two large multijunction launchers allow to couple up to 6 MW at a frequency of 3.7 GHz. (author) 3 refs., 8 figs