Transport of intense LH pulses into a tokamak plasma

Abstract

Application of lower-hybrid (LH) power in short, intense pulses in the 5–10 GW range should overcome the limiting effects of Landau damping, and thereby permit the penetration of LH power into the interior of large-scale plasmas. We show that, under such very intense LH pulses, wave coupling may deteriorate because of nonlinear density changes due to the ponderomotive force effects in front of the grill. Ponderomotive forces are also likely to induce strong plasma bias and consequent poloidal and toroidal plasma rotation. Although backward electric currents, created in the plasma by intense LH pulses, dissipate a large portion of the radio frequency power absorbed, the current drive efficiency is acceptable. We use a numerical simulation of wave–particle interactions to analyse the applicability of standard quasilinear theory to the case of large energy flux densities. The initial results indicate the existence of important restrictions on the use of the quasilinear approximation. The results of the present paper also indicate that some of the effects considerably alter some ideas of Cohen et al.