Effects of Added Hexapole Magnetic Fields and Preionization in Theta Pinch Experiments

Abstract

A hexapole magnetic field has been superimposed on the fast magnetic mirror compression field of the Scylla III θ pinch in an attempt to stabilize an observed plasma instability. The instability is of the flute type with a superimposed rotation. The effect of the hexapole field on the plasma stability was studied with streak camera photography and through observation of the neutron emissions. Under certain conditions the hexapole ``stabilizing'' field has an observable effect on the instability. Its main effect is to symmetrize the rotation about the axis of the compression coil and to produce a delay in the onset of the instability. There is at most a small effect tending to symmetrize the time distribution of neutron emission and to increase the neutron yield. An ionized deuterium plasma is produced by a fast, low energy capacitor bank coupled directly to the single‐turn compression coil of the Scylla III device. The ``afterglow'' of this preionization discharge, uniformly permeated by a magnetic bias field B₀, forms the initial condition for the application of the main magnetic compression field. The effect of the main compression field on the preionized plasma depends strongly on the B₀ which exists in the plasma.