Numerical Studies of the Plasma Focus

Abstract

The dynamical formation and structure of the plasma focus has been studied with a two-dimensional numerical fluid model. The extremely high kinetic energy densities obtained in the numerical fluid experiment as the result of adiabatic compression and viscous heating agree well with experiment. Three features in the plasma focus are isolated: an anode cold source, a hot pinch region, and an axial shock. The anomalously long lifetime of the plasma focus is shown to be the result of axial flow, with stabilization of magnetohydrodynamic modes through the ion stress tensor in the intermediate collisionless, collision-dominated regime. Estimates of the neutron yield based on the numerical fluid experiment concur with experimental yields, and are the result of thermally reacting deuterons in the hot pinch region. The plasma parameters of interest determined from the hot pinch region suggest that the ion distribution function will not have a simple Maxwellian form and this in particular may account for the discrepancy with experiment on the anisotropy in space of the neutron yield.