Anomalous Self-Generated Electrostatic Fields in Nanosecond Laser-Plasma Interaction

TL;DR

This study investigates the electrostatic fields generated during nanosecond laser interactions with plasma, revealing discrepancies between measurements and simulations that suggest complex underlying physics like turbulence.

Contribution

The paper presents experimental measurements of strong electrostatic fields in laser-plasma interactions and highlights the limitations of current models, emphasizing the need for advanced kinetic simulations.

Findings

Measured fields up to 110 MV/m cannot be reproduced by existing models.

Strong thermal electron pressure gradients may be linked to ion acoustic turbulence.

Current simulations lack the ability to fully capture nonlinear laser-plasma dynamics.

Abstract

Electrostatic (E) fields associated with the interaction of a well-controlled, high-power, nanosecond laser pulse with an underdense plasma are diagnosed by proton radiography. Using a current 3D wave propagation code equipped with nonlinear and nonlocal hydrodynamics, we can model the measured E-fields that are driven by the laser ponderomotive force in the region where the laser undergoes filamentation. However, strong fields of up to 110 MV/m measured in the first millimeter of propagation cannot be reproduced in the simulations. This could point to the presence of unexpected strong thermal electron pressure gradients possibly linked to ion acoustic turbulence, thus emphasizing the need for the development of full kinetic collisional simulations in order to properly model laser-plasma interaction in these strongly nonlinear conditions.