Effect of Kilo-Tesla Magnetic Fields on Ignition and Burn Dynamics in Fast Ignition Laser Fusion*)

In fast ignition laser fusion, electron beam guiding with a kilo-tesla magnetic field has been proposed to avoid divergence of the beam, which significantly enhances the core heating efficiency. In addition to beam guiding, magnetic fields affect electron heat conduction and alpha particle energy transport. The objective of this study is to estimate the effect of a magnetic field on ignition and burn propagation dynamics of a high-gain target in fast ignition (FI) laser fusion based on axially symmetric two-dimensional burn simulations. A uniformly compressed DT plasma sphere with a cylindrical hot spot was assumed as the initial condition. A magnetic field of 100 kT was applied along the symmetrical axis. In the ignition phase, the suppression of the alpha particle flux and heat conduction by the magnetic field fastens temperature rise in the hot spot. However, the magnetic field reduced the burn propagation speed and then increased the burning time, which enhanced the erosion of the fuel edge by rarefaction waves and decreased the effective areal density of the fuel. Consequently, the burnup fraction for a 100 kT magnetic field was 11% lower than that without a magnetic field.