Review of tokamak experiments on direct electron heating and current drive with fast waves

Abstract

Results from tokamak experiments on direct electron interaction with the compression Alfven wave (‘fast wave’) are reviewed. Experiments aimed at electron heating as well as those in which fast wave electron drive was investigated are discussed. A distinction is drawn between experiments employing the lower hybrid range of frequencies, where both the lower hybrid wave (‘slow wave’) and the fast wave can propagate in much of the plasma, and those experiments using the fast wave in the range of moderate to high ion cyclotron harmonics, where only the fast wave can penetrate to the plasma core. Most of the early tokamak experiments were in the lower hybrid frequency regime, and the observed electron interaction appeared to be very similar to that obtained with the slow wave at the same frequency. In particular, electron interaction with the fast wave was observed only below a density limit nearly the same as the well known slow wave density limit. In the more recent lower fequency fast wave experiments, electron interaction (heating and current drive) is observed at the center of the discharge, where slow waves are not present.