MODELING OF RF CURRENT DRIVE IN THE PRESENCE OF RADIAL DIFFUSION

The kinetic theory of radiofrequency current drive in tokamak plasmas is investigated. The problem of the impact of anomalous transport on t he driven current profile and efficiency is considered in detail. Amon g the possible candidates for explaining anomalous transport in tokama ks, magnetic turbulence is known to have a strong influence on the dyn amics of superthermal electrons and is assumed here to be the basic me chanism responsible for radial diffusion of the rf-driven current. The 3-dimensional kinetic equation in the presence of rf heating and magn etic turbulence is studied. Its properties are first investigated by a non-local response function technique. Both the adjoint formalism and the Langevin equations method are extended to the case of radially di ffusing electrons. The full kinetic equation is numerically solved by means of a 3-D Fokker-Planck code. Applications to lower-hybrid curren t drive are presented and several kinetic effects are discussed.