Abstract
A systematic study of the thermal behaviour of ion cyclotron range of frequencies (ICRF) antenna front faces was undertaken on the Tore Supra tokamak over two years of plasma operation, by means of infrared (IR) and visible light cameras. Among the variety of edge-antenna interaction phenomena observed experimentally, the present paper focuses on the most deleterious effect for ICRH operation, a non-resonant radio-frequency (RF) process causing hot spots on the Faraday screen and bursts of metallic impurities. The hot spots phenomenology (time history, location) is presented. Their magnitude is characterized by semi-quantitative indicators, defined from the IR and visible light films. This makes possible a parametric study of the antenna–plasma interaction, over a wide range of experimental configurations. The roles of the local RF electric field and of the edge density regimes in the spurious process are outlined. The observed hot spot behaviour is compatible with the build-up of RF sheaths. Some ways of reducing the problems are suggested.