RF-sheath physics assessment of Tore Supra ICRF antenna designs

In 1998 the operation of Tore Supra ICRF antennas was perturbed by hot spots on a Faraday Screen and metallic impurity production [1]. The process responsible for the antenna-plasma interaction is suspected to be linked with RF-sheaths [2]. Modifications of the antenna front face were implemented to ease these problems, and were tested on plasma in 1999. These changes in the launcher structure, as well as the parametric variations of the heat loads onto the antenna front faces, are assessed numerically with respect to RF-sheath effects. The simulation tool used combines, in realistic geometry, 3-D RF near-field computation, field line tracing and particle transport calculation to evaluate mappings of sheath-induced heat fluxes [3]. Simulated heat loads show similar parametric dependencies as surface temperatures measured in 1998/99, and the results stress the need to compute the density patterns together with RF potential maps.