Current Sustainment by Lower Hybrid Waves in the WT-2 Tokamak

Abstract

When RF power P_LHH near the lower hybrid frequency is injected into the ohmically heated plasma in the WT-2 tokamak, the RF-driven current is generated (I_rf\simeq12 kA) and the plasma (n_e\simeq3×10¹² cm⁻³) is sustained by this current without ohmic current during the injection of P_LHH. The efficiency of RF current drive is obtained as I_rf=0.06P_LHH⁄n_e·R (kA, kW, 10¹³ cm⁻³, m), where R is the major radius. The current I_rf is carried by suprathermal electrons which interact resonantly with lower hybrid waves. A high frequency instability and associated relaxation oscillation are observed, which can be suppressed by a simultaneous injection of the electron cyclotron heating power.