MODELING OF LOWER-HYBRID CURRENT DRIVE IN THE PRESENCE OF SPATIAL RADIAL DIFFUSION

A code to solve the full three dimensional Fokker-Planck kinetic equat ion in the presence of lower hybrid current drive (LHCD) is applied to study numerically the problem of modelling LHCD, including the combin ed effects of spatial radial diffusion and an electric field The code uses the Beliaev-Budker relativistic collision operator, and applies a method of fractional steps to the numerical solution of the time evol ution equation for the three dimensional Fokker-Planck equation. The i mportance of the numerical approach associated with an exact relativis tic treatment for the solution is emphasized in order to study accurat ely all the physics associated with this problem, especially the shape of the distribution function and the physics associated with its hot tail as, for instance, the fast electron transport and lower hybrid ab sorbed power profiles. The aim of the simulation is to match hard X ra y imaging profiles and current density profiles. An accurate relativis tic treatment of the hot tail helps make the study of these problems l ess phenomenological and more physical. Some preliminary results from the Tokamak de Varennes (TdeV) are analysed in order to illustrate the power of the method.