Quantifying Anomalous Field Structure in Inertial Confinement Fusion-Relevant Laser–Target Interactions

On the occasion where spherical direct-drive implosion experiments have been radiographed with protons, an anomalous structure corresponding to strong electric or magnetic fields has been measured extending millimeters from the target surface. These fields have the ability to affect late-time laser–target interactions and potentially act as an energy sink, where laser energy is contained in the field outside the target. To better understand the source, effect, and strength of these fields, simplified experiments were conducted in planar geometry on the OMEGA EP laser at the Laboratory for Laser Energetics. These planar experiments varied the target material, target size, pulse shape, and intensity, and measured the field structure using concurrent proton radiography along multiple lines of sight and a 4ω probe. By probing along multiple lines of sight, we can better interpret the field type and strength, and eliminate certain possibilities. We present the analysis of these radiographs, which indicate that these fields are predominantly electric and highly dependent on laser intensity.