Influence of a Toroidal Field on Plasma Confined in a Toroidal Octupole
D. E. Lencioni, J. W. Poukey, J. A. Schmidt, J.
C. Sprott, and C. W. Erickson
University of Wisconsin, Madison,
(Received 24 July 1967; final manuscript received 10 January 1968)
A toroidal magnetic field B-theta of up to 360 G was added to the Wisconsin
toroidal octupole producing a stellarator-like field with a large rotational
transform and large shear. The influence of this B-theta on plasma injection,
transport, density distribution, lifetime, and electric-field fluctuations
was studied. Injection and transport were not inhibited by B-theta and
proceeded in much the same way as for B-theta = 0. The density distribution
after filling was unchanged and remained peaked slightly off the separatrix
toward the hoops. The lifetime was smaller with B-theta, but was still
consistent with expected losses to the hoop supports. In the originally
V'' unstable region outside the last stable field line, the amplitude of
the electric field fluctuations decreased when B-theta was added, but in
the interior of the plasma, the fluctuations increased monotonically with
B-theta. In the plasma interior the maximum diffusion coefficient derived
from the fluctuations increased from 10^-4 D-Bohm to 10^-2 D-Bohm as B-theta
was increased from zero to 140 G, but the observed lifetime, limited by
hoop supports, was always ~ 10 tau-Bohm. Large potential deviations which
were affected by magnetic field perturbations occurred in the region of
zero average shear. Large external-field perturbations were added with
no effect on the lifetime. Fluctuations associated with stable inverted
density gradients were reduced or eliminated by B-theta.
Ref: D. E. Lencioni, J. W. Poukey, J. A. Schmidt, J.
C. Sprott, and C. W. Erickson, Phys. Fluids 11, 1115-1125, (1968)
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