Burn Propagation in Magnetized High-Yield Inertial Fusion

TL;DR

This study investigates how magnetic fields influence burn propagation in inertial confinement fusion, revealing regimes of thermal conduction, alpha transport, and suppression, with implications for optimizing high-yield fusion designs.

Contribution

It provides the first detailed analysis of magnetized burn propagation regimes using radiation-MHD simulations in ICF, highlighting effects of magnetic fields on implosion dynamics and burn behavior.

Findings

Magnetic fields can suppress or channel burn propagation depending on orientation.

Anisotropic conduction significantly affects ablation rates during stagnation.

Magnetized implosions show altered shape and burn dynamics, impacting high-yield fusion strategies.

Abstract

Recent experiments at the National Ignition Facility (NIF) have demonstrated ignition for the first time in an inertial confinement fusion (ICF) experiment, a major milestone allowing the possibility of high energy gain through burn propagation. Use of external magnetic fields, applied primarily to reduce thermal losses, could increase hotspot temperature and ease requirements for ignition, opening up the capsule design space for high energy gain. However, this same restriction of thermal transport has the potential to inhibit burn propagation, which is vital in the attainment of high gain. In this work, radiation-magnetohydrodynamics (MHD) simulations carried out using the code Chimera are used to investigate the effect of a pre-imposed magnetic field on ignition and burn propagation. This paper studies the propagation of burn using both an idealized planar model and in fully-integrated 2D MHD simulations of an igniting NIF capsule. A study of magnetised burn propagation in the idealized planar model identifies three regimes of magnetized burn propagation: (1) thermal conduction driven; (2) alpha transport driven; and (3) fully suppressed burn. Simulations of NIF shot N210808 with an applied 40T axial field show clear indication of burn suppression perpendicular to field lines, with rapid burn observed along field lines. Implosion shape is altered by the field, and anisotropic conduction causes significant modification to the rate of ablation during stagnation. These results highlight the fundamental changes to implosion dynamics in high yield magnetized ICF and motivate further study to better optimize future magnetized target designs for high gain.