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Torsatron and stellarator plasma confinement devices rely on magnetic surface mapping to determine the critical vacuum magnetic field structure. A recently developed method employing an emissive filament offers some advantages over the traditional technique of mapping with a directed electron beam. On the Auburn torsatron a comparative study between the emissive filament and directed electron beam techniques has been conducted. The parameters varied in the comparative study are filament geometry, emission current, bias voltage, background gas pressure, and magnetic field strength. This comparative study indicates that the emissive filament technique is reliable over a broad and easily accessible range of parameters. We have also measured the spatial distribution of electrons on a given magnetic surface. As an application of the emissive filament technique, the optimization of the magnetic surfaces on the Auburn torsatron is shown.
Gandy et al. (1987) studied this question.