Observations of Electromagnetic Fields and Plasma Flow in Hohlraums with Proton Radiography

We report on the first proton radiography of laser-irradiated hohlraums. This experiment, with vacuum gold (Au) hohlraums, resulted in observations of self-generated magnetic fields with peak values ~10⁶ G. Time-gated radiographs of monoenergetic protons with discrete energies (15.0 and 3.3 MeV) reveal dynamic pictures of field structures and plasma flow. Near the end of the 1-ns laser drive, a stagnating Au plasma (~10 mg cm^-3) forms at the center of the hohlraum. This is a consequence of supersonic, radially directed Au jets (~1000 μm ns^-1, ~Mach 4) that arise from the interaction of laser-driven plasma bubbles expanding into one another.