Nonlinear drift wave induced plasma transport

The foremost obstacle to be overcome in achieving a successful fusion power reactor is the insulation of the intense thermonuclear plasma from its cold surroundings for a time sufficient to satisfy the Lawson Criteria. Now that gross plasma stability has been achieved in a variety of confinement systems attention is being redirected towards the variety of microinstabilities capable of exciting anomalous thermal and particle transport. Perhaps the most important of these instability modes are those which are driven by the radial gradients of plasma density and temperature. Although the waves excited in most experiments are measured under conditions where the nonlinear limit has been reached detailed comparisons with theory have usually been possibly only for certain linear properties. Experiments conducted in realistic confinement geometries, and including the effects of such accessories as plasma limiters, have been unable to relate the mode spectra to the transport observed. Indeed, the saturation mechanisms for the instabilities are not yet agreed upon. In the present experiment we are studying collisional drift waves excited in a particularly simple geometry, and under conditions which can be diagnosed in a straightforward fashion using conventional probes. It is hoped that in this way, a contribution might be made toward the understanding of the nonlinear development of plasma transport processes which may be found in future reactor regimes