Proton probing measurements of filamentary electromagnetic structure in laser ablation of solids

TL;DR

This study uses proton radiography and experiments to analyze filamentary electromagnetic fields in laser ablation of solids, revealing their dependence on laser energy, target material, and the role of Weibel instability.

Contribution

It provides experimental evidence linking filamentary electromagnetic structures to the expansion driven Weibel instability in laser-target interactions.

Findings

Filamentary fields are influenced by laser energy and target Z.

Proton radiography effectively visualizes these electromagnetic structures.

Secondary Weibel instability is identified as the primary driver.

Abstract

Proton radiography of laser direct-drive spherical implosions has shown anomalous structures that correspond to strong electric or magnetic fields extending throughout the corona. These fields have the ability to affect laser-target interactions and act as an energy sink. To better understand the these fields, simplified experiments were conducted in planar geometry on the OMEGA EP laser at the Laboratory for Laser Energetics. Varying target material, target size, pulse shape, and intensity, and measured the field structure using dual-axis proton radiography and a 4w probe. Proton radiographs were analyzed and quantitatively demonstrate that the growth of these features is dominated by laser energy and target Z. The data strongly supports that a secondary instability as a consequence of the expansion driven Weibel instability in these interactions is the primary driver for these fields.