Plasma experiments in the Scyllac toroidal theta pinch

Experiments on plasma equilibrium and stability in the Scyllac full torus, and in earlier 5-m and 8-m toroidal sectors, are reported. In all these experiments, the outward toroidal drift was compensated by a combination of l = a helical and l = 0 bumpy fields generated by shaping the inner surface of the compression coil or by driven l = 1 windings. Time-resolved measurements of the gross plasma column motion, plasma radius, excluded flux, external magnetic field, plasma density, electron and ion temperatures, and plasma beta have been made. Preliminary results show that the plasma behavior in the 8-m sector and the full torus (both with major radius R = 4 m) is qualitatively the same, with a well-defined, theta-pinch-type plasma column being formed in both cases. No plasma shredding or evidence of microinstabilities is seen, and no m greater than or equal to 2 modes have been observed. The plasma confinement lasts typically 6 to 10 $mu$s, and is terminated by a long-wavelength, m = 1-type motion which carries the plasma column to the wall with an effective growth rate of 0.5 to 1.0 x 10$sup 6$ s$sup -1$. Photographs from a 360$sup 0$ framing camera mounted on themore » torus axis show this motion to consist of at least n = 0, 1, and 2, where m and n describe motions of the form exp i(mTHETA-nz/R). A net toroidal current of 1 to 1.5 kA flowing opposite to B$sub 0$ has been measured; this current appears to be too small to account for the experimental growth rate in terms of the current-driven Kruskal--Shafranov mode. (auth)« less