PLASMA-SURFACE INTERACTIONS WITH ICRF ANTENNAS AND LOWER-HYBRID GRILLS IN TORE-SUPRA

The edge plasma interactions of the actively cooled radio-frequency he ating launchers in Tore Supra ion-cyclotron range of frequencies (ICRF ) antennas and lower-hybrid (LH) grills are studied using infrared vid eo imaging. On the two-strap ICRF antennas, operated in fast-wave elec tron heating or current drive mode, hot spots with temperatures of 500 -900 degrees C are observed by the end of 2 s power pulses of 2 MW per antenna. The steady-state temperature distribution is determined prin cipally by the relative phase of the two antenna straps: dipole (heati ng) phasing results in significantly less antenna heating than does 90 degrees (current drive) phasing. Transient heat fluxes of 1-20 MW/m(2 ) are measured on the lateral protection bumpers at ICRF turn-on; thes e fluxes are primarily a function of plasma and radio frequency (rf) c ontrol. The remarkable feature of the lower hybrid edge interaction is the production of beams of heat flux in front of the grills; these be ams propagate along the helical magnetic field lines and can deliver f luxes of 5-10 MW/m(2) over areas of several cm(2) to plasma-facing com ponents. Both the ICRF and LH phenomena appear to result from the acce leration of particles by the near fields of the launchers. Modeling of the heat flux deposition on components and its relation to sputtering processes is presented.