Deep-learning-enabled Bayesian inference of fuel magnetization in magnetized liner inertial fusion

Journal Article · 01 September 2021 · Physics of Plasmas

DOI: https://doi.org/10.1063/5.0056749 · OSTI ID:1820420

Lewis, William E.  ^[1]; Knapp, Patrick F.  ^[1]; Slutz, Stephen A.  ^[1]; Schmit, Paul F.  ^[1]; Chandler, Gordon A. ^[1]; Gomez, Matthew R.  ^[1]; Harvey-Thompson, Adam J.  ^[1]; Mangan, Michael A. ^[1]; Ampleford, David J.  ^[1]; Beckwith, Kristian  ^[1]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Fuel magnetization in magneto-inertial fusion (MIF) experiments improves charged burn product confinement, reducing requirements on fuel areal density and pressure to achieve self-heating. By elongating the path length of 1.01 MeV tritons produced in a pure deuterium fusion plasma, magnetization enhances the probability for deuterium–tritium reactions producing 11.8-17.1 MeV neutrons. Nuclear diagnostics thus enable a sensitive probe of magnetization. Characterization of magnetization, including uncertainty quantification, is crucial for understanding the physics governing target performance in MIF platforms, such as magnetized liner inertial fusion (MagLIF) experiments conducted at Sandia National Laboratories, Z-facility. We demonstrate a deep-learned surrogate of a physics-based model of nuclear measurements. A single model evaluation is reduced from $\mathcal{O}(10–100)$(10–100) CPU hours on a high-performance computing cluster down to $\mathcal{O}(10–100)$(10) ms on a laptop. This enables a Bayesian inference of magnetization, rigorously accounting for uncertainties from surrogate modeling and noisy nuclear measurements. The approach is validated by testing on synthetic data and comparing with a previous study. We analyze a series of MagLIF experiments systematically varying preheat, resulting in the first ever systematic experimental study of magnetic confinement properties of the fuel plasma as a function of fundamental inputs on any neutron-producing MIF platform. We demonstrate that magnetization decreases from $BR\sim 0.2$~0.5 to $BR\sim 0.2$~0.2 MG cm as laser preheat energy deposited increases from $E_{\text{preheat}}\sim 460$~460 J to $E_{\text{preheat}}\sim 460$~1.4 kJ. This trend is consistent with 2D LASNEX simulations showing Nernst advection of the magnetic field out of the hot fuel and diffusion into the target liner.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0003525
• OSTI ID: 1820420
• Report Number(s): SAND--2021-9789J; 698980
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 9 Vol. 28; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English