Heat flux to the material surfaces in the scrape-off layer of a tokamak plasma is investigated experimentally. The time response of heat flux measurement has been improved to 0.2 ms by the recently developed thin-film thermometer. The result shows that the heat flux is calculated from a simple sheath model including secondary electron emission effects even if epithermal electrons are present.
Synchronous quenching of drift-wave instability is investigated experimentally. The measurements show resonance phenomena similar to that of ion-sound instability. The result is quantitatively compared with a phenomenological theory which includes a linear growth and a nonlinear saturation source term.
Experimental studies on the origin of metal impurities in DIVA are described. Three processes of metal impurity release, i.e. ion sputtering, evaporation and arcing, have been identified. Among these processes, ion sputtering is the dominant process in the quiet phase of the discharge, which is characterized by the lack of spikes in the loop voltage as well as by the fact that no heat flux concentration towards a specific part of the first wall takes place. Moreover, it is demonstrated that a honeycomb structure can decrease the metal impurity release.
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