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 during the 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, 1 MW LH system on HT-7 superconducting tokamak. In these experiments, usually LH power is between 200 similar 400 kW, 2 ⩽ N_// ^p ⩽ 3 (ΔN_// = 0.8), and rf pulse in 500 ms. Sometimes, the sawtooth oscillation is 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 lengthening sawtooth and a saturation of sawtooth oscillations are also observed during our experiments.