Abstract
During ohmic heating of plasma confined in a Stellarator it is observed that the plasma moves across the magnetic confining field at a much higher average velocity than is predicted by classical considerations. An attempt has been made to compare the observed velocity with the calculated drifts that should result from the measured randomly varying electric fields and density gradients present in the plasma. It is found that the random quantities, as measured by double probes, are of sufficient intensity to give order-of-magnitude agreement between observed and calculated velocities. A new hypothesis is put forward to explain the origin of these high-amplitude fluctuations, a hypothesis which might be applicable to gas discharges generally. It is assumed that the non-Maxwellian electron distribution resulting from the applied electric field excites large amplitude, coherent plasma oscillations near the plasma frequency. These large amplitude oscillations act as the `pump' in the non-linear process known as parametric amplification. Thermal fluctuations, normally present with small amplitudes in quiescent plasmas, are amplified over a wide band of frequencies, both above and below the pump frequency, by the resulting parametric amplifier action of the plasma. This results in high-amplitude noise which might produce enhanced diffusion and rapid thermalization effects.