Bayesian inference of inaccuracies in radiation transport physics from inertial confinement fusion experiments

TL;DR

This paper introduces a Bayesian approach to infer inaccuracies in radiation transport physics from inertial confinement fusion experiments, accounting for complex models and experimental noise, but finds limited reconciliation of simulation and experimental discrepancies.

Contribution

It presents a novel Bayesian inference method incorporating experimental and prior uncertainties to evaluate microphysics models from fusion experiment data.

Findings

Evidence of inaccuracies in X-ray drive intensity calculations

Detection of errors in Ge L-shell absorption models

Modifications to radiation transport do not fully reconcile simulations with experiments

Abstract

First principles microphysics models are essential to the design and analysis of high energy density physics experiments. Using experimental data to investigate the underlying physics is also essential, particularly when simulations and experiments are not consistent with each other. This is a difficult task, due to the large number of physical models that play a role, and due to the complex (and as a result, noisy) nature of the experiments. This results in a large number of parameters that make any inference a daunting task; it is also very important to consistently treat both experimental and prior understanding of the problem. In this paper we present a Bayesian method that includes both these effects, and allows the inference of a set of modifiers which have been constructed to give information about microphysics models from experimental data. We pay particular attention to radiation transport models. The inference takes into account a large set of experimental parameters and an estimate of the prior knowledge through a modified $\chi^{2}$ function, which is minimised using an efficient genetic algorithm. Both factors play an essential role in our analysis. We find that although there is evidence of inaccuracies in off-line calculations of X ray drive intensity and Ge $L$ shell absorption, modifications to radiation transport are unable to reconcile differences between 1D HYDRA simulations and the experiment.