The numerical computation of the preionization phase of a toroidal pinch discharge

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Abstract
Using the two-dimensional MHD computer code ANIMAL. The authors have computed the plasma dynamics of the preionization phase of a toroidal pinch. The physical model includes electron and ion thermal conduction, electron-ion resistivity, electron-neutral resistivity, ionization, dissociation, and line radiation all based on local thermodynamic equilibrium. The code uses ADI finite difference equations with improved boundary conditions which enable the code to follow the oscillatory motion of the plasma. A coupled electrical circuit calculation is performed. The physical model requires the specification of a minimum ionization fraction fmin to set an upper bound on the resistivity. By suitably choosing fmin, they reproduce many of the features of the preionization discharge. Our calculations have suggested a new electrical diagnostic, the measurement of intervals between zero-crossings of current and flux, which is used to help normalize the computations.