Interferometric studies of plasma density fluctuations propagating along the major radius in ZT-40M, using time-delayed correlation techniques

Plasma density fluctuations in the ZT-40M reversed-field pinch have been observed (at frequencies <500 kHz) with a multichord interferometer whose chords are vertical and separated in major radius. Time-delayed correlations between density fluctuations on the different paths determine a major-radial velocity in the range several *10 6 cm s -1 . At the highest observed frequencies a global m=1 perturbation affects this speed. At lower frequencies the observed propagation is consistent with ion-acoustic waves or drift-modes (or a mixture of both) localized in the outer region of the discharge.