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Electron Heating in Strongly Beaded High-Z Pinch Discharges at High Densities.

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Technical rept.,

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The late-time, fully-developed stage of sausage-like beading of z-pinch discharges can give rise to enhanced electron heating and thus enhanced radiative losses, caused by Ohmic anomalous heating in the constricted regions. In this report, this transfer of energy from condensations of magnetic field energy to radiation is examined quantitatively, based on a simplified dynamical model for the nonlinear instability driving terms. Constricted portions of the discharge, with low density and cross-section, and mostly or entirely anomalous current, alternate with the higher density beads, which carry current classically. The extreme limit of this phenomenon is that of multiple diodes in series, with the nearly-evacuated low density regions considered as bipolar-flow diodes, with pinched electron flow. In all probability, the low-density regions cannot evacuate to the extent required for such vacuum-diode behavior. The overall resistive heating rate is of course VI, with the total current I given by appropriate circuit equations, but the local heating rates for electrons in the low density regions are balanced by increased radiative loss when these hotter electrons collide with the denser blobs of plasma. The blobs cannot respond hydrodynamically to the increased heating before radiation loses the deposited energy.

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  • Plasma Physics and Magnetohydrodynamics

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