Sawtooth Activity during Lower Hybrid Current Drive Experiment in HT-7 Superconducting Tokamak

It has been found that lower hybrid waves excite various sawtooth oscillations duringthe HT-7 tokamak discharges. In this paper we present the results of lower hybrid current drive(LHCD) on sawtooth activity in a series of experiments with 2.45 GHz, l MW LH system onHT-7 superconducting tokamak. In these experiments, usually LH power is between 200~ 400kW, and rf pulse in 5oO ms. Sometimes, the sawtooth oscillationis accompanied by a wide range of magnetohydrodynamic activity in the plasma central region,normally with a m = 1/n =1 mode. A LHCD partial suppression of sawtooth, a lengthebogsawtooth and a saturation of sawtooth oscillations are also observed during our experiments.