ICRF heating in TFR and the problem of impurity release

The efficiency of ICRH in TFR was limited by an important influx of metallic impurities in the plasma core. Using carbon limiters and different materials for the antennas Faraday shield leads to a significant decrease of the metallic impurity content: in contrast with the previous results, the increase of temperature associated with the RF pulse remains now constant for more than 0.1 s. However, the power radiated by the metallic ions at the end of the RF pulse still reaches an appreciable fraction of the total RF power, particularly when using an antenna generating the RF wave from the low magnetic field side of the plasma. This effect is attributed to an interaction of the RF wave with the low density plasma located in the scrape off layer. (author)