Dependence of EC-Driven Current on the EC-Wave Beam Direction in LHD

抄録

Electron cyclotron current drive (ECCD) experiments were conducted in the Large Helical Device to investigate the characteristics of EC-driven current and its profile and the possibility of controlling current and rotational transform profiles by ECCD. Successful ECCD helps prevent magnetohydrodynamic instabilities in plasmas. Scanning the EC-wave beam direction with a long pulse width of 8 s revealed a systematic change in the plasma current. The current's direction was reversed by a reversal of the beam direction. The direction agrees with the prediction of Fisch-Boozer theory regarding EC-wave beam injection from low-field side. The maximum driven current is 9 kA with an EC-wave power of 100 kW. The optimum beam direction that maximizes the driven current is investigated with the help of ray-tracing code. This direction depends on the magnetic field, efficiency of power absorption, and fraction of the power absorbed by trapped electrons.