DYNAMICS OF RF PRODUCTION OF STELLARATOR PLASMAS IN THE ION-CYCLOTRONRANGE OF FREQUENCY

The present study investigated numerically the process of r.f. product ion of plasma in the URAGAN-3M torsatron in the frequency range below the ion cyclotron frequency (omega < omega(ci)). The dynamics of r.f. plasma build-up at the stages of neutral gas burnout and plasma heatin g were studied using a zero-dimensional transport code, in which the p lasma confinement law was determined by large helical device scaling. Two models for input r.f. power were used. In the first case, the r.f. power absorbed by the electrons was computed by a one-dimensional r.f . code solving Maxwell's boundary problem equations. The mechanisms of electron heating through direct excitation of the slow wave (SW) by a ntennae as well as the conversion of fast wave (FW) into SW in the vic inity of Alfven resonance (scenario of Alfven heating) were taken into account in the computations. In the second case, an 'ideal' model of r.f. power deposition onto the electrons as a linear function of plasm a density was employed. A noticeable difference in plasma production d ynamics computed for these two cases was found. Better agreement with experimental data obtained from the URACAN-3M torsatron was found for the first case resulting from combination of the one-dimensional r.f. and zero-dimensional transport codes.