Absorption of magnetoacoustic waves in high beta plasmas

The oscillations of a radially inhomogeneous high-β plasma column are investigated experimentally and theoretically. The high-β plasma is produced by a theta pinch discharge. The waves are launched during the post implosion phase in the frequency range of about 1 MHz. The spatial distribution of the wave fields is determined and a high absorption is observed. The absorption of magnetoacoustic waves is an efficient mechanism to heat a plasma. It was investigated under various conditions in the past. In this paper we present theoretical and experimental investigations in the transition region from the collision dominated to the collisionless regime. In the theoretical treatment the linearised MHD-equations are used where viscous and resistive effects are included. (orig./HT)