Spectroscopic study and energy balance of pulsed toroidal discharges

Abstract

Investigations of plasma produced by a pulsed current of 40 kA peak and 20 mu s decay time in a quartz torus of major radius 32 cm and minor radius 4 cm in 30 mtorr of hydrogen are described. The electron temperature rose in 1 mu s to approximately 4*104K and relaxed by 4 mu s to a value of approximately 2*104K for most of the 50 mu s duration of the current pulse. Corresponding electron densities were 3*1015 cm-3, falling to a nearly steady value of 1.5*1015 cm-3. At later times the afterglow is followed to 8*1013 cm-3 at 180 mu s. Dissipation of the toroidal current provides 15 to 20 times the energy required for full ionisation, and temperature equilibrium results from atom thermal conduction loss to the wall. Although these losses can be intrinsic, the observed asymmetries in luminosity and magnetic field show that MHD instability is present which enhances the wall contact.