Multi-fluid modeling of an SFS Z-pinch accelerator

The Zap Energy sheared-flow-stabilized (SFS) Z-pinch concept relies on a coaxial plasma accelerator to ionize, heat, and accelerate plasma that forms the pinch in the assembly region. Constructing a complete numerical model of an accelerator discharge requires neutral gas physics, breakdown processes, ionization, radiation, material electron emission models, neutral recycling, magnetized sheaths, and the Hall effect. In order to capture many of these non-ideal processes self-consistently, Zap is developing multi-fluid modeling, built from a two-fluid (ion-electron) model. To guide and validate modeling development, Zap uses experimental data and synthetic diagnostics to indicate where physics sub-models (e.g. sheath boundary conditions, radiation) need improvement. This work emphasizes comparisons of simulation results with spectroscopic temperature and laser interferometry density measurements. Preliminary results indicate that extended single fluid models that include Hall, two-temperature, and Braginksii-like transport terms cannot explain observed temperatures and radial mass distributions. MHD models are extended with neutrals and recycling at walls to replicate measured temperatures, and a two-fluid (ion-electron) model that allows charge separation and sheath formation is implemented to explain observed radial density profiles.