On the interaction of MHD waves with a plasma surrounded by a cold gas-mantle

Abstract

In cold gas-mantle systems a partially ionized boundary layer is formed which becomes highly resistive to the magnetoacoustic waves. Especially below the ion gyro frequency ωci the effective resistivity due to ion-neutral collisions can attain values being an order of magnitude higher than the Spitzer resistivity. Thus , a substantial part of the r.f. power available at the antenna can be damped in such a layer. The application of the r.f. power in the Alfven wave frequency range of the internal ring device FLASK IVA (FIVA) results in a relatively powerful plasma heating. The plasma-neutral gas balance is strongly modified by this power input, as well as the plasma equilibrium which becomes a sensitive function of the neutral gas content of the plasma. An r.f. power of the order of 0.5 MW is absorbed in the plasma. The parameters and the perpendicular dimension of the discharge are in the range which is typical for the layers which will form in the immediate vicinity of the wall in a fully developed mantle of a fusion device. Thus the presented data indicate that a strong interaction between the MHD waves and such cold layers should be expected.