Processes terminating radiative collapse in a hydrogen fiber Z pinch

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Abstract
The processes terminating radiative collapse, of relevance to the present generation of hydrogenic fiber Z pinch experiments, are identified and discussed. Computational analogs for these processes are developed and used to modify a basic model consisting of a one-dimensional (1-D) Lagrangian resistive magnetohydrodynamic (MHD) code, coupled to a model of a realistic external circuit. A radiation transport package, tailored to the problem, is used to simulate radiation energy transfer within the pinch. Other effects accounted for include modification of the electron transport coefficients for high electron magnetization as well as the effect of free-electron degeneracy upon electron transport coefficients, the equation of state, and the opacity. Results suggest that termination is dominated by rapid changes in the radial profiles of both degenerate electron pressure and the radiation energy loss per unit volume (the gradient of the latter profile changing sign as the high-density pinch core becomes optically thick to lower frequencies). The termination process is shown to be a hybrid of radiation transport and free-electron degeneracy effects for all line densities considered, with electron degeneracy becoming increasingly important at lower line densities.