CURRENT DRIVE WITH FAST WAVES, ELECTRON-CYCLOTRON WAVES, AND NEUTRAL INJECTION IN THE DIII-D TOKAMAK

Current drive experiments have been performed on the DIII-D tokamak us ing fast waves, electron cyclotron waves, and neutral injection. Fast wave experiments were performed using a 4-strap antenna with 1 MW of p ower at 60 MHz. These experiments showed effective heating of electron s, with a global heating efficiency equivalent to that of neutral inje ction even when the single pass damping was calculated to be as small as 5%. The damping was probably due to the effect of multiple passes o f the wave through the plasma. Fast wave current drive experiments wer e performed with a toroidally directional phasing of the antenna strap s. Currents driven by fast wave current drive (FWCD) in the direction of the main plasma current of up to 100 kA were found, not including a calculated 40 kA of bootstrap current. Experiments with FWCD in the c ounter current direction showed little current drive. In both cases, c hanges in the sawtooth behavior and the internal inductance qualitativ ely support the measurement of FWCD. Experiments on electron cyclotron current drive have shown that 100 kA of current can be driven by 1 MW of power at 60 GHz. Calculations with a Fokker-Planck code show that electron cyclotron current drive (ECCD) can be well predicted when the effects of electron trapping and of the residual electric field axe i ncluded. Experiments on driving current with neutral injection showed that effective current drive could be obtained and discharges with ful l current drive were demonstrated. Interestingly, all of these methods of current drive had about the same efficiency, 0.015 x 10(20) MA/MW/ m2.