Scott Brandon

A finite element formulation of the Darwin PIC model for use on unstructured grids

In this paper we introduce a new formulation of the Darwin approximation of Maxwells equations and discuss its domain of applicability. We describe our finite element implementation of this model, allowing the use of unstructured grids, and its coupling with a PIC method for the particles.

Zonal flow generation in inertial confinement fusion implosions

A supervised machine learning algorithm trained on a multi-petabyte dataset of inertial confinement fusion simulations has identified a class of implosions that robustly achieve high yield, even in the presence of drive variations and hydrodynamic perturbations. These implosions are purposefully driven with a time-varying asymmetry, such that coherent flow generation during hotspot stagnation forces the capsule to self-organize into an ovoid, a shape that appears to be more resilient to shell perturbations than spherical designs. This new class of implosions, whose configurations are reminiscent of zonal flows in magnetic fusion devices, may offer a path to robust inertial fusion.

Ensemble simulations of inertial confinement fusion implosions

The achievement of inertial confinement fusion ignition on the National Ignition Facility relies on the collection and interpretation of a limited (and expensive) set of experimental data. These data are therefore supplemented with state-of-the-art multidimensional radiation-hydrodynamic simulations to provide a better understanding of implosion dynamics and behavior. We present a relatively large number (∼ 4000) of systematically perturbed 2D simulations to probe our understanding of low-mode fuel and ablator asymmetries seeded by asymmetric illumination. We find that Gaussian process surrogate models are able to predict both the total neutron yield and the degradation in performance due to asymmetries. The surrogates are then applied to simulations containing new sources of degradation to quantify the impact of the new source.

A HYDRA UQ workflow for NIF ignition experiments

We describe the use of our in-transit workflow infrastructure to run an ensemble of HYDRA [1] [2] Inertial Confinement Fusion (ICF) simulations in support of experiments conducted using the National Ignition Facility (NIF) laser. We discuss how our approach can be used to gain deeper insight into NIF experiments.We ran over 60,000 2D HYDRA simulations and generated over a billion synthetic x-ray images during 8 weeks on the Trinity Cray XC40 system. These represent a majority of all 2D simulations run during HYDRAs 20 year history. We implemented a producer-consumer in-transit framework to minimize the amount of disk space used to generate synthetic x-ray images. We describe our infrastructure and approach, and explore the scaling and performance issues we ran into. Our goal is to help others plan for large ensemble simulations and discuss changes to system software that would make it easier to run large ensembles.

A study of heavy-ion beams during longitudinal compression using particle simulation☆

Abstract Particle simulations show that during longitudinal compression there is little growth in beam longitudinal and transverse emittance. Both longitudinal