Lower hybrid current drive and sustainment in WT-2 tokamak

The lower hybrid current drive experiments have been carried out in the WT-2 tokamak. The rf power is injected near the end of tokamak discharge by the four waveguides array. The plasma can be sustained by the rf driven current only during the rf injection period. The scaling of the rf driven current and the density limit are studied. The density limit exists and it depends on the energy distribution of electrons in the ohmically heated initial plasmas. The maximum value obtained in the present experiments is 1.4 x 1013 cm-3. The high frequency instability associated with the rf driven current has been studied and found it can be stabilized by the electron cyclotron heating. (AUth.)