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Abstract
The relationship between relaxation and particle diffusion in the Proto S-1/C spheromak has been studied. The plasma was formed in a magnetic configuration which was not the minimum energy Taylor state, and went through a period of relaxation before its magnetic configuration was that of the Taylor state. Early in the relaxation phase, the internal and external magnetic fluctuations were corre- lated and it was found that at the time of peak amplitude they had a radial structure of a tearing mode. After the reconnection of these modes, the plasma continued to evolve towards the Taylor state with only small magnetic fluctuations at the center of the plasma.
The local particle diffusion coefficient was measured in these Proto S-1/C discharges. The technique used was to inject a delta function source of impurities into the plasma and observe the motion of the impurities relative to the flux surface. It was found that, during the decay phase of the spheromak discharge, when the plasma was in a Taylor state, the carbon diffusion coefficient was explained classically. While the plasma was relaxing towards the Taylor state, the diffusion coefficient was 2 (TURN) 4 times larger than classical. At this time, the plasma was not yet force-free. This non-classical diffusion appears to have been caused by (upsilon)(,(,Ex)(,B)) velocities due to correlations between the fluctuating electric field and density. Because the (upsilon)(,(,Ex)(,B)) velocity acts on all of the plasma species similarly, the anomalous hydrogen particle diffusion coefficient should have been as large as that of carbon.
