Fully kinetic simulations of effects beyond resisitive magnetohydrodynamics at the edge of a dense z-pinch

Low-density plasmas have an important role in pulsed-power experiments. They can divert power flow and change macroscopic plasma dynamics in lab astro experiments. However, the resistive magnetohydrodynamic (MHD) codes traditionally used to model these experiments cannot capture low-density effects, such as the Hall term or anomalous resistivity. Thus, it is not well understood which of these additional effects are relevant to current experiments and need to be included in models. In this work, we use fully kinetic particle-in-cell (PIC) simulations of the low-density edge region of a z-pinch to study beyond-MHD physics. By calculating electric field components, we show that the Hall and electron pressure terms are the dominant contributions to Ohm's law in this regime. We demonstrate that PIC can recreate both the microscopic behaviour of the Hall term as charge separation and macroscopic fluid-like behaviour. We compare PIC and Hall MHD simulations of a z-pinch m=0 mode, showing an axial shear in the direction of current flow due to the Hall effect. We conclude by discussing why PIC is a challenging tool for steep density gradients and highlight the ideal features for codes modelling this problem.