Plasma Behavior in a Cusp-Mirror Magnetic Field

Abstract

A plasma containment device has been constructed in which an attempt has been made to combine the basic stability advantages of a four-pole line cusp with the low loss rate of a mirror field. The magnetic field was produced by the addition of the mirror field orthogonally to the cusp field. Using pulse techniques an ionized gas was created within a biconical chamber and a magnetic field produced transiently with the mirror field along the axis of the chamber (Z axis) and the cusp field in the X-Y plane. Measurements with magnetic probes and light pipes show that a disturbance in the magnetic field accompanied by an increase in light intensity started at the periphery of the plasma chamber and was propagated inward at two velocities to the central axis. Detailed measurements made on the magnetic-field configuration indicate that, at the time of arrival of the second wave at the axis, the mirror field had been to a large extent separated from the cusp field so that mostly mirror field existed throughout the central region, while mostly cusp field existed in the outer region. The intensity of the field at this time in the central region indicates that the cusp field was compressing the plasma and mirror field so that the intensities of the mirror field in this region were even larger than the maximum intensity of the applied mirror field.