Kinetic Simulations of Gas Breakdown on MJ-scale Dense Plasma Focus Device*

Dense plasma focus (DPF) Z-pinches are compact pulse power driven devices with coaxial electrodes.  The discharge of DPF consists of three distinct phases: first generation of a plasma sheath, plasma rail gun phase where the sheath travels down the electrodes and finally an implosion phase where the plasma stagnates into a z-pinch geometry.  The plasma on axis rapidly goes unstable and can produce a short, intense pulses of fast ions and neutrons when deuterium is used as the working gas. The magnitude of the neutron yields produced scales strongly with the current delivered to the pinch.  Preventing parasitic current pathways, which can be generated at each stage of the DPF discharge, is critical to getting high neutron yield.  The most straightforward source of parasitic current pathways is incomplete breakdown or poor liftoff of the plasma sheath during the early stage of the discharge.  This work is focused on understanding the dynamics of the initial plasma sheath using fully-kinetic simulations with the particle-in-cell (PIC) code LSP for a MJ-scale DPF in an axisymmetric geometry with deuterium. Effects of varying the electrode geometry, initial gas fill and driving voltage will be presented.