Enhancement of Pressure Perturbations in Ablation due to Kinetic Magnetised Transport Effects under Direct-Drive ICF relevant conditions

TL;DR

This study uses kinetic simulations to show that self-generated magnetic fields can significantly amplify pressure perturbations in laser-driven plasma ablation, affecting the uniformity of inertial confinement fusion targets.

Contribution

First kinetic 2D Vlasov-Fokker-Planck simulations including magnetic fields and ion outflow demonstrate magnetic field-induced inversion and enhancement of pressure perturbations in ablation.

Findings

Magnetic fields invert and amplify pressure perturbations even at low Hall parameters.

The mechanism is robust across various plasma conditions and perturbation wavelengths.

Magnetic fields increase nonuniformity at the ablation surface and favor lower mode enhancements.

Abstract

We present for the first time kinetic 2D Vlasov-Fokker-Planck simulations, including both self-consistent magnetic fields and ablating ion outflow, of a planar ablating foil subject to nonuniform laser irradiation. Even for small hall parameters ($\omega \tau_{ei} \lesssim 0.05$) self-generated magnetic fields are sufficient to invert and enhance pressure perturbations. The mode inversion is caused by a combination of the Nernst advection of the magnetic field and the Righi-Leduc heat-flux. Non-local effects modify these processes. The mechanism is robust under plasma conditions tested; it is amplitude independent and occurs for a broad spectrum of perturbation wavelengths, $\lambda_p = 10-100\,$\mu m$. The ablating plasma response to a dynamically evolving speckle pattern perturbation, analogous to an optically smoothed beam, is also simulated. Similar to the single mode case, self-generated magnetic fields increase the degree of nonuniformity at the ablation surface by up to an order of magnitude and are found to preferentially enhance lower modes due to the resistive damping of high mode number magnetic fields.