ENHANCED HEAT-FLUX IN THE SCRAPE-OFF LAYER DUE TO ELECTRONS ACCELERATED IN THE NEAR-FIELD OF LOWER-HYBRID GRILLS

As a result of experimental observations of localized heat flux on com ponents magnetically connected to radiating waveguides in Tore Supra a nd in TdeV, the acceleration of electrons near lower hybrid (LH) anten nas has been investigated. A simple analytical model has been develope d to compute the dynamics of the particles in the near field approxima tion. Landau damping of the very high N-parallel to (20 < N-parallel t o < 100) component of the launched spectrum on the thermal electrons o f the scrape-off layer (SOL) is found to occur. Simulation of a typica l LH pulse in Tore Supra indicates that the electrons can be accelerat ed up to 2-3 keV. Modelling of the interaction of this fast electron p opulation with the edge plasma allows a calculation of the heat flux o n plasma facing components that are magnetically connected to the ante nna. Model results and the results of experiments in Tore Supra and Td eV are compared. The calculated heat fluxes are found to be fairly con sistent when the variation of convective heat flux at the grill apertu re is taken into account. From this analysis, it is concluded that, fo r an LH power density of 25 MW/m(2), the resulting heat flux along the field lines (3.5 MW/m(2)) is manageable for the components connected to the antenna, provided that good coupling can be maintained at a low density in front of the grill.