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Extensive investigations of ICRF-induced effects on the edge plasma and on plasma-wall interaction were conducted on TEXTOR under different wall, limiter, plasma and heating conditions. Several strong effects of ICRF on the edge parameters were observed on TEXTOR such as density rise, instantaneous electron heating, modification of SOL profiles, influx of light and/or heavy impurities, increased heat flux to the limiters, and production of energetic ions in the SOL. The fast response time of some of the changes and the observation of a maximum in the SOL profile of electron temperature, heat flux and metal sputtering clearly demonstrated that RF power is directly absorbed in the SOL. Estimates of this power amount to several percent of the total RF power launched into the plasma. Plasma-wall interaction during ICRF was substantially reduced by an appropriate choice of the wall conditioning procedures. As a result, long pulse, high power, low impurity operation was possible. Further improvement was obtained by ICRF antenna phasing. Experimental and theoretical studies were performed to elucidate the mechanisms responsible for the ICRF-induced effects, including the propagation of plasma waves in the edge plasma and nonlinear phenomena such as parametric decay, important changes in the DC current between the antenna structure and the liner due to the sheath effect at the antennas, and the generation of waves at harmonics of the RF generator frequency. Radial profiles of the DC radial and poloidal electric fields as well as a localised RF electric field structure were measured in the SOL using a fast scanning probe.

Additional information

Authors: VAN OOST G ET AL., Ecole Royale Militaire, Bruxelles (BE);WEYNANTS R R, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE);DIPPEL K H ET AL., University of California, Los Angeles (US);CONN R W ET AL.,
Bibliographic Reference: Article: Fusion Engineering and Design, Vol. 12 (1990) pp. 149-170
Record Number: 199011666 / Last updated on: 1994-12-02
Original language: en
Available languages: en