INFLUENCE OF THE ALFVEN WAVE SPECTRUM ON THE SCRAPE-OFF LAYER OF THE TCA TOKAMAK
The study of the Scrape-Off Layer (SOL) during Alfv'en wave heating may lead to a better understanding of the antenna-plasma interaction and therefore also of the impurity production. The SOL of the TCA tokamak has been widely investigated by means of Langmuir probes. In previous experiments we demonstrated that the SOL reacts sensitively to different antenna designs. The aim of the present work is to present in detail the influence of the Alfv'en wave spectrum on the SOL. The experiments have shown that the plasma boundary layer is strongly affected by the RF. In particular, it was found that the excited wave spectrum strongly influences the ion density, the electron temperature and the floating potential. Even minor fine structures of the wave spectrum are reproduced in these raw data. In TCA, as the spectrum evolves due to a density rise during the RF phase, the passage of the Alfv'en continua and their associated eigenmodes (discrete modes) is observed. In general, a strong depletion in the edge density of up to 70% is observed in the continuum part of the wave spectrum. During the crossing of an eigenmode a density increase is observed. The floating potential becomes negative during the continua and even more negative crossing the eigenmode. This behaviour is a function of the power transmitted to the plasma through the antennae. We also found a change in the behaviour of the scrape-off layer parameters at a power of around 100 kW. The profiles of the basic parameters are also modified, depending on the wave spectrum. MHD mode activity which can occur during the RF phase considerably alters the behaviour mentioned above. Furthermore, the similar behaviour of some of the core plasma parameters suggests a strong dependence between the boundary and the core plasma. Finally, the modulation of the RF power allows us to characterize the difference in coupling, for the continua and the eigenmodes, between the Alfv'en wave field and the scrape-off layer.
Bibliographic Reference: 15TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA HEATING, DUBROVNIK (YUGOSLAVIA), MAY, 16-20, 1988, AVAILABILITY: CEC-LUXEMBOURG, DG-XIII-C-3, POB 1907, MENTIONING PAPER EN 34070 ORA
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Record Number: 1989126118700 / Last updated on: 1989-06-01
Available languages: en