Simulations of a Dense Plasma Focus on a High-Impedance Generator

Naval Research Laboratory is starting to study the connection between plasma instabilities and fast ion acceleration for neutron production on a dense plasma focus (DPF). The experiments will be performed on the HAWK generator (665 kA) that has a fast rise time, 1.2 μs, and a high inductance, 720 nH. There is a conjecture that the neutron yield on a DPF may be enhanced on a high-impedance generator, since the assembly on the axis will not significantly reduce the current drive. Furthermore, to prevent the upstream breakdown during the implosion, there are plans to inject the gas load as plasma far from the insulator stack. As an introductory study, we performed MHD simulations using the Athena code. Athena is a Eulerian 3-D, unsplit finite volume MHD code that includes shock capturing with Riemann solvers and resistive diffusion for the magnetic field components. The simulations are coupled to an equivalent circuit model for HAWK. We report the dynamics and implosion time as a function of the initial injected plasma distribution and study the implications of nonideal effects. We also calculated a stochastic particle acceleration resulting from the motional electric field.