Weibel instability drives large magnetic field generation in laser-driven single plume ablation

TL;DR

This paper uses kinetic simulations to show that the ion Weibel instability causes significant magnetic field generation in laser-driven plasma plumes, impacting inertial confinement fusion experiments.

Contribution

It reveals that the ion Weibel instability dominates magnetic field growth in expanding plasmas, a novel insight into plasma behavior in fusion conditions.

Findings

Filamentary magnetic fields reach ~100 T at large focal radii.

The ion Weibel instability grows within 100 ps and produces density oscillations.

Magnetic and density perturbations can influence heat transport and laser absorption.

Abstract

First-principles kinetic simulations are used to investigate magnetic field generation processes in expanding ablated plasmas relevant to laser-driven foils and hohlraums. In addition to Biermann-battery-generated magnetic fields, strong filamentary magnetic filaments are found to grow in the corona of single expanding plasma plumes; such filaments are observed to dominate Biermann fields at sufficiently large focal radius, reaching saturation values of $\sim$ 100 T at National Ignition Facility-like drive conditions. The filamentary fields result from the ion Weibel instability driven by relative counterstreaming between the ablated ions and a sparse background population, which could be the result of a gas prefill in a hohlraum or laser pre-pulse. The ion-Weibel instability is robust with the inclusion of collisions and grows on a timescale of 100 ps, with a wavelength on the scale of 100-250 $\mu$m, over a wide range of background population densities; the instability also gives rise to coherent density oscillations. These results are of particular interest to inertial confinement fusion experiments, where such field and density perturbations can modify heat-transport as well as laser propagation and absorption.