High power lower hybrid coupling and investigation of fast electron dynamics in Tore Supra

Lower hybrid current drive experiments carried out on Tore Supra in various plasma configurations are presented. First, the problem of wave-plasma coupling and interaction with the plasma edge is discussed. It is found that high power coupling as well as power transmission capabilities are particularly sensitive to the plasma size and the safety factor q. Different behaviours were also observed for limiter/ergodic divertor configurations or ohmic/ICRH preheated discharges. At the same time an anomalous heat flux was observed on the guard limiter of the grills. In the second part of the paper, lower hybrid power modulation experiments aimed at the investigation of fast electron dynamics are described. This study combines several diagnostics specific to superthermal electrons (hard X ray emission, electron cyclotron emission and transmission) with advanced modelling tools. Three relevant time constants of the fast electron distribution driven by the lower hybrid waves have been measured and identified with radial diffusion, collisional slowing down and pitch angle scattering, respectively. 3-D Fokker-Planck simulations are found to be in excellent agreement with the experimental results. (author). 3 refs, 4 figs