Biermann Battery Magnetic Fields in ICF Capsules: Total Magnetic Flux Generation

TL;DR

This paper develops a model to understand magnetic flux generation in ICF implosions, highlighting how perturbations influence magnetic field formation and providing tools to predict magnetic effects in target designs.

Contribution

The paper introduces a scaling model for magnetic flux in ICF hot-spots, linking perturbation characteristics to magnetic flux generation and enabling better prediction of MHD effects.

Findings

Larger amplitude and higher mode number perturbations generate more magnetic flux.

Magnetic flux generation peaks during stagnation when gradients are largest.

The model can estimate magnetic field strengths from simulation data.

Abstract

This paper focuses on the process of magnetic flux generation in ICF implosions. Hot-spots are shown to be dominated by fields generated during stagnation, when the temperature and density gradients are largest. A scaling of hot-spot magnetic flux is derived and compared with simulations, revealing that perturbations with both larger amplitudes and higher mode numbers generate more magnetic flux. The model allows for greater understanding of which target designs will be susceptible to MHD effects. For example, the model can be used to ascertain the time when most magnetic flux is generated. If generation is weighted more towards early times, then more high-mode magnetic field loops will be present. A hot-spot with no high-mode perturbations at time of peak neutron production can still contain significant magnetic flux on those scales. By assuming that magnetic flux is deposited at the hot-spot edge by Nernst advection, the model can be used to post-process radiation-hydrodynamics data to estimate magnetic field strengths and magnetizations.