Fast Wave Current Drive on Diii - D

The physics of electron heating and current drive with the fast magnetosonic wave has been demonstrated on DIU-D , in reasonable agreement with theoretical modeling. A recently completed upgrade to the fast wave capability should allow f id noninductive current drive in steady state advanced confinement discharges and provide some current density profile control for the Advanced Tokamak Program. DIII-D now has three four-strap fast wave antennas and three transmitters, each with nominally 2 MW of generator power. Extensive experiments have been conducted with the fist system, at 60 M H Z , while the two newer systems have come into operation within the past year. The newer systems are configured for 60 to 120 MHz. The measured FWCD efficiency is found to increase linearly with electron temperature as y = 0.4 x lo1* 5 " ' (keV) [A/m2W], measured up to central electron temperature over 5 keV. A newly developed technique for determining the internal noninductive current density profile gives ef€iciencies in agreement with this scaling and profiles consistent with theoretical predictions. Eu1 noninductive current drive at 170 kA was achieved in a discharge prepared by rampdown of the Ohmic current. Modulation of microwave reflectometry signals at the fast wave frequency is being used to investigate fast wave propagation and damping. Additionally, rfpick-up probes on the internal boundary of the vessel provide a comparison with ray tracing codes, with clear evidence for a toroidally directed wave with antenna phasing set for current drive. GENERAL ATOMICS REPORT GA-A22039 1 FAST WAVE CURRENT DRTVE ON DIII-D deGrclcrcrie et al. There is some experimental evidence for fast wave absorption by energetic beam ions at high cyclotron harmonic resonances.