Shock Front Field Structure in Low-density Systems

It is known that shock front is not a simple discontinuity as depicted in commonly used hydro codes but consists of selfgenerated fields [1]. A quasi-planar platform using broadband proton radiography has been developed to study the field structure at a shock front. The broad bandwidth offers energy-dependent measurements which quantitatively constrain both the potential and field width at the shock front. Experiments were conducted on the OMEGA EP, where three long pulse beams delivered 6 kJ in 2 ns for shock initiation in a gas filled tube and a short pulse of 850 J, 10 ps generated broadband protons for point-projection radiography. Simultaneous spatially resolved soft-x-ray spectroscopy provided shock velocity, particle velocity and thermal emission measurements, constraining density and temperature for the field generation. The data and modeling indicate that a multi-KeV potential was present at the shock front where a strong electron pressure gradient existed.