Global Eigenmode Analysis of The Filamentation Instability in a Dense Plasma Focus

A dense plasma focus (DPF) is an open-ended coaxial plasma gun that terminates in a short-lived Z-pinch configuration on axis. DPFs operating with a deuterium fill produce a pulse of neutrons as the Z-pinch goes unstable. The neutron yield scales strongly with the pinch current. A poor breakdown/lift-off of the plasma along the insulator can lead to current restrikes, diverting current away from the pinch and decreasing the yield. The breakup of the plasma into filaments, which is a result of an electrothermal instability, has been observed in many experiments during the lift-off stage and is one possible source of poor lift-off. In this work, the filamentation instability during the lift-off stage of a DPF is studied using a global eigenmode description based on the extended-magnetohydrodynamic (EMHD) equations. This model incorporates the anode and insulator geometry into the analysis, which in some scenarios is found to have a large influence on the mode number and growth rate of the fastest growing modes. Results from 1D fully kinetic simulations of the lift-off are used as background conditions for the global eigenmode analysis.