Broadband fluctuations and particle transport in the edge plasma during ECRH in DITE

Abstract

Measurements of edge broadband magnetic field, density and electric field fluctuations up to 300 kHz have been performed in DITE Ohmic and electron cyclotron resonance heated (ECRH) plasmas. Detailed characterization of the structure of the magnetic fluctuations has been obtained using measurements in different poloidal and toroidal locations and radial profiles in the scrape-off layer. The cross-field particle flux driven by electric field and density fluctuations has been measured and found to be comparable to the total particle outflow measured by Langmuir probes embedded in the limiters. In particular, the increase of particle transport during ECRH is completely accounted for by the increase of electric field and density fluctuations. Magnetic fluctuations also increase during ECRH but do not contribute significantly to particle transport and are probably simply a consequence of the perpendicular and parallel currents driven by pressure fluctuations. In the conditions of the experiment, the edge response is not due to direct interaction of the radiofrequency with the boundary plasma, but rather to the effects of the thermal wave propagating from the absorption zone.