The influence of resonance particle escape on the lower-hybrid current drive

The dependence of current-drive efficiency on the shape of lower-hybrid wave spectra is investigated theoretically. The interaction of plasma electrons with lower-hybrid waves is described by a set of quasilinear equations. Its solution is used for estimating the driven current. The optimum wave spectrum for an efficient current drive is found. As shown, at non-optimum spectra current-drive efficiency is substantially reduced by a significant loss of fast particles. The current-drive efficiencies are calculated for various plasma and incident wave parameters used in several actual experiments. The mechanism described in the paper might explain the existing disagreement between the theoretical predictions and the results of most present experiments. (J.U.)