High-fidelity three dimensional MHD simulations of argon gas-puff Z-pinches

Summary form only given. We have performed 3-D, resistive, magnetohydrodynamic (MHD) simulations with MACH3 of argon gas-puff Z-pinches inside an array of 12 current return posts from realistic initial conditions using a collisional radiative equilibrium (CRE) model to predict K-shell and L-shell radiation output. Initial gas puff conditions, including densities, temperatures, and velocities were imported from a 2-D azimuthally symmetric simulation of gas flow using an equation of state including the latent heat of fusion from cluster formation. The simulation geometry included an axisymmetric, but otherwise complete representation of the Titan Pulsed Sciences Division 12 cm diameter nozzle with 2 cm recess and central jet. These initial conditions exhibit and explain all the shock structures observed in planar laser induced fluorescence density measurements of the experimental gas flow, and are more complete as they include velocity and temperature information. In addition to the non-uniform, though azimuthally symmetric, initial state of the gas puff from the nozzle flow, the simulations include azimuthal perturbations in the magnetic field from the surrounding array of return current posts. The physics simulated during the pinch includes electron and ion thermal diffusion as well as resistive diffusion and MHD. A tabular CRE model for argon from the radiation hydrodynamics branch of the Naval Research Laboratory produces electron temperature and ionization from which an ideal gas model determines pressure and internal energy. The probability of escape is assumed constant rather than computed, so the simulations do not include opacity effects self-consistently. The thermal conductivities and resistivities are determined using classical Spitzer-Braginskii formulations also based on the CRE model's temperatures and ionization. The inhibiting effect of the magnetic field on the thermal conductivities is likewise included. A self-consistent circuit model with parameters and open-circuit voltage waveform appropriate for the Decade Quad is employed to determine the applied current. These simulations use an energy-based model to derive the voltage across the pinch and show good energy conservation between the external circuit and the pinch domain throughout. Comparisons of results of MACH2 and MACH3 simulations of axially and radially uniform axisymmetric initial gas fills show that MACH3 results extend those of MACH2 and conserve energy as well