Current drive by the combined effects of electron-cyclotron and Landau wave damping in tokamak plasmas

Abstract

The theory of current drive by the combined effects of lower-hybrid and electron-cyclotron wave absorption is investigated. The case of a spatially homogeneous lower-hybrid diffusion coefficient and the electron ordinary mode propagating nearly normal to the magnetic field is considered. The effect of selective electron-cyclotron wave absorption for optimizing lower-hybrid current drive is discussed for two situations, namely, the wave frequency close to or much less than the electron-cyclotron gyrofrequency, which corresponds to particle heating for moderate velocities and mildly relativistic energies, respectively. In the former case, by using the numerical solution of the Fokker–Planck equation it is shown that electron heating is suited for controlling the density of the current-carrying tail. The latter case is investigated for moderate wave powers and is shown to be most appropriate for optimizing the ratio J/P.