Simulating Hotspot Formation in Wire X-pinches

X-pinches are pulsed-power driven devices where a current is passed through two or more wires that cross in an “X” configuration. The neck forms a micro Z-pinch structure due to an enhanced Lorentz force, resulting in brightly emitting regions. These intense ‘hotspots’ have small spatial extents (~1-10 μm) and short temporal durations (~10 ps), making X-pinches commonly used for point-projection radiography [1]. Several experimental studies have been conducted to characterise X-pinch performance in terms of wire number, material, etc., however the hotspot conditions are still not fully understood. Spectral analysis has previously inferred temperatures up to a few keV and near solid densities [2], however these are challenging measurements due to resolution limitations and extreme environments.

Numerical studies of X-pinches are similarly resolution-limited, and therefore typically employ assumptions of symmetry, either in the azimuthal or axial direction. However, this neglects 3D behaviours due to the finite radii wires. This work presents high resolution 3D simulations of X-pinch experiments using Chimera, a radiation-MHD code with static mesh refinement, in order to study 3D effects on crossing point dynamics. The sensitivity of model parameters such as radiation treatment is first discussed using reduced 2D simulations. The morphology of X-pinch features such as the characteristic axial jet is then compared against experiment using synthetic diagnostics. Finally, the plasma parameters in highly compressed hotspots are compared in simulations of experiments on lower (200 kA) and higher current (800 kA) generators.

[1] Pikuz, S. A., Shelkovenko, T. A., & Hammer, D. A. (2015). X-pinch. Part II. Plasma Physics Reports, 41(6), 445–491.

[2] Shelkovenko, T. A., Sinars, D. B., Pikuz, S. A., & Hammer, D. A. (2001). Radiographic and spectroscopic studies of X-pinch plasma implosion dynamics and x-ray burst emission characteristics. Physics of Plasmas, 8(4), 1305–1318.