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

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 these fields, simplified experiments were conducted in planar geometry on the OMEGA extended performance laser at the Laboratory for Laser Energetics. Field structure was measured using dual-axis proton radiography for experiments that varied target material, target size, pulse shape, and intensity. Proton radiographs were analyzed and quantitatively demonstrate that the growth of these features is dominated by incident laser energy and target Z. The data are consistent with a secondary, electrostatic instability established by the expansion-driven Weibel instability as the primary driver for these fields in these interactions.