Operation of a reversed field pinch without a conducting shell

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Abstract
The Reversatron reversed field pinch (R/a=50 cm/8 cm) [IEEE Trans. Plasma Sci. PS-14, 267 (1986)] has been operated with and without an aluminum shell surrounding the resistive toroidal vacuum chamber. Discharges without the shell have the same density, fluctuation level, and dynamo activity as seen in discharges with the shell; however, the plasma current and discharge duration are reduced. With zero reversal of the toroidal field the reversed field pinch (RFP) becomes a spheromak of high aspect ratio. Discharges without the shell in this mode are also of lower current and shorter duration. The early terminations may be caused by the tilt instability. In all cases discharges in helium were of longer duration than those in hydrogen.