Biblio

The MagNIF team at LLNL is developing a pulsed power platform to enable magnetized inertial confinement fusion and high energy density experiments at the National Ignition Facility. A pulsed solenoidal driver capable of premagnetizing fusion fuel to 40T is predicted to increase performance of indirect drive implosions. We have written a specialized Python code suite to support the delivery of a practical design optimized for target magnetization and risk mitigation. The code simulates pulsed power in parameterized system designs and converges to high-performance candidates compliant with evolving engineering constraints, such as scale, mass, diagnostic access, mechanical displacement, thermal energy deposition, facility standards, and component-specific failure modes. The physics resolution and associated computational costs of our code are intermediate between those of 0D circuit codes and 3D magnetohydrodynamic codes, to be predictive and support fast, parallel simulations in parameter space. Development of a reduced-order, physics-based target model is driven by high-resolution simulations in ALE3D (an institutional multiphysics code) and multi-diagnostic data from a commissioned pulser platform. Results indicate system performance is sensitive to transient target response, which should include magnetohydrodynamic expansion, resistive heating, nonlinear magnetic diffusion, and phase change. Design optimization results for a conceptual NIF platform are reported.

The fundamental limits of high-current conduction and response of metal conductors to large, fast current pulses are of interest to high-speed fuses, exploding wires and foils, and magnetically driven dynamic material property and inertial confinement fusion experiments. A collaboration between the University of Nevada, Reno, University of New Mexico, and Sandia National Laboratory has fielded an electrically thick (R 400-μm \textbackslashtextgreater skin-depth) cylindrical metal rod platform in a Z-pinch configuration driven by the Sandia 100-ns, 900-kA Mykonos linear transformer driver 1 . Photonic Doppler velocimetry (PDV) measuring the expansion velocity of the uncoated surface of aluminum rods 2 was used to benchmark equation of state (EOS) and electrical conductivity models used in magnetohydrodynamics simulations using the Los Alamos National Laboratory (LANL) code FLAG 3 . The metal surface was found to expand along the liquid-vapor coexistence curve in density-temperature space for 90 ns of the rod’s expansion for both tabular EOSs with Van der Waals loops and with Maxwell constructions under the vapor dome. As the slope of the coexistence curve varies across EOS models, the metal surface in simulation was found to heat and expand at different rates depending on the model used. The expansion velocities associated with EOS models were then compared against the PDV data to validate the EOS used in simulations of similar systems. Here, the most recent aluminum EOS (SESAME 93722) 4 was found to drive a simulated velocity that best compared with the experimental data due to its relatively steep coexistence curve and high critical point.

Auto-magnetizing (AutoMag) liners 1 have demonstrated strong precompressed axial magnetic field production (\textbackslashtextgreater100 T) and remarkable cylindrical implosion uniformity during experiments 2 on the Z accelerator. However, both axial field production and implosion uniformity require further optimization to support use of AutoMag targets in magnetized liner inertial fusion (MagLIF) experiments. Recent experimental study on the Mykonos accelerator has provided data on the initiation and evolution of dielectric flashover in AutoMag targets; these results have directly enabled advancement of magnetohydrodynamic (MHD) modeling protocols used to simulate AutoMag liner implosions. Using these modeling protocols, we executed three-dimensional MHD simulations focused on improving AutoMag target designs, specifically seeking to optimize axial magnetic field production and enhance cylindrical implosion uniformity for MagLIF. By eliminating the previously used driver current prepulse and reducing the helical gap widths in AutoMag liners, simulations indicate that the optimal 30-50 T range of precompressed axial magnetic field for MagLIF can be accomplished concurrently with improved cylindrical implosion uniformity, thereby enabling an optimally premagnetized magneto-inertial fusion implosion with high cylindrical uniformity.

Fast, accurate three dimensional reconstructions of plasma equilibria, crucial for physics interpretation of fusion data generated within confinement devices like stellarators/ tokamaks, are computationally very expensive and routinely require days, even weeks, to complete using serial approaches. Here, we present a parallel implementation of the three dimensional plasma reconstruction code, V3FIT. A formal analysis to identify the performance bottlenecks and scalability limits of this new parallel implementation, which combines both task and data parallelism, is presented. The theoretical findings are supported by empirical performance results on several thousands of processor cores of a Cray XC30 supercomputer. Parallel V3FIT is shown to deliver over 40X speedup, enabling fusion scientists to carry out three dimensional plasma equilibrium reconstructions at unprecedented scales in only a few hours (instead of in days/weeks) for the first time.