Improvement of RF current drive density limit in the JFT-2M tokamak

Experiments combining lower hybrid current drive (LHCD) with the injection of a solid pellet have been carried out to study the potential of this approach for optimizing LHCD. The injected pellet is observed to penetrate deeply into the plasma, producing a peaked electron density profile. An improvement of the density limit of LHCD is obtained although this effect seems to be short lived. In addition, good particle confinement and suppression of MHD activity are also observed during relatively high density LHCD. New results of 200 MHz fast wave experiments for electron densities well above the LH resonance density, using a phased four-loop antenna array, are also reported. It is observed that in discharges with electron cyclotron heating (ECH) of 180 kW the injection of 300 kW of fast wave power produces an appreciable drop in the loop voltage and a noticeable enhancement of electron cyclotron emission (ECE) from non-thermal electrons near the plasma centre. The drop in loop voltage and the enhancement of ECE are also observed to depend on the phase difference between adjacent loop antennas, a result consistent with theory. These results suggest fast wave current drive. (author). 3 refs, 2 figs