We de-cribe here a numerical model of a free boundary axisymmetric tokaraak plasma and its associated control systems.The plasma is modeled v>ith a hybrid method using two-dimensional velocity and flux functions with surface-averaged MHO equations describing the evolution of the adiabatic invariants. Equations are solved for the external circuits and for the effects of eddy currents in nearby conductors. The method is verified by application to several test problems and used to simulate the formation of a bean-shaped plasma in the PBX experiment.

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The free-boundary, axisymmetric tokamak simulation code TSC is used to model the transport time-scale evolution and positional stability of the Princeton Beta Experiment (PBX). A disruptive thermal quench will cause the plasma column to move inwards in major radius. It is shown that the plasma can then lose axisymmetric stability, causing it to displace exponentially off the midplane, terminating the discharge. The accuracy of the code is verified by modelling several controlled experimental shots in PBX.