Enhanced Hot Electron Preheat Observed in Magnetized Laser Direct-Drive Implosions

TL;DR

This study demonstrates that applying a 10 T magnetic field in direct-drive implosions enhances hot electron preheat and alters electron confinement, impacting fusion performance and emphasizing the need to control laser-plasma instabilities.

Contribution

It provides experimental evidence that magnetic fields influence hot electron behavior and preheat in direct-drive implosions, revealing new dynamics in magnetized inertial confinement fusion.

Findings

Magnetic field increases hot electron preheat by 1.5 times.

Magnetized implosions confine hot electrons, affecting capsule charging.

Energy of charged-fusion products decreases with magnetization.

Abstract

Hard x-ray emission, associated with hot electron preheat, in direct-drive implosions was observed to be enhanced by a factor of $1.5\pm0.1$ by application of a $10$ T magnetic field. The applied magnetic field reaches a quasi steady-state aligned with the ablation flow prior to the onset of laser-plasma instabilities in the corona. Hot electrons that would otherwise escape the corona and lead to capsule charging in unmagnetized implosions are confined in a mirror-mode of the magnetic field in magnetized implosions. These hot electrons are shown to subsequently pitch-angle scatter from the mirror onto the capsule, thereby leading to the observed hard x-ray generation in magnetized implosions. Consequently, the energy of charged-fusion products, associated with the capsule charging, are observed to decrease when the implosion is magnetized. These results intensify the need to mitigate laser-plasma instabilities -- particularly for magnetized implosions -- to maximize fusion gain and implosion efficiency.