Background: The Nike laser facility is the world’s largest krypton fluoride laser facility that is utilized to study laser matter interactions under conditions expected for laser fusion. Nike’s capability to provide extremely uniform focal profiles and its deep UV wavelength facilitate the conducting of experiments with laser-produced shocks with negligible effects from laser imperfections and laser plasma instability. Sinusoidal ripples are laser-machined into the front (laser illuminated) or rear target surface to study the effect of target non-uniformity on the interaction physics. By varying the laser intensity the pressure applied to the target can be varied from that of high explosives (hundreds of kilobars) to the multi-megabar pressures needed for inertial fusion implosions. Nike has extensive x-ray imaging diagnostics to track the propagation of shocks through matter and the effects of growth of uniformities in the target due to t-shocks.
Accomplishments: Two major advances were made in the effects of shocks on the evolution of targets with surface non-uniformity.
1) For the first time, detailed measurements were made that revealed the ringing behavior in the areal mass density when targets were impulsively shocked with short laser pulses (300 ps) where the shock transit time was less than the laser pulse length.
2) The transition to the regime where jets were emitted from targets with ripples on their rear surface of laser-shocked targets was observed as the laser-produced shock amplitude was reduced to pressures where this phenomenon has been observed in experiments utilizing high explosives. The transition is theoretically linked to the transition from liquid-like target rear surface material behavior at moderately high pressures to gas-like or plasma-like behavior at higher pressures.
Significance: These experiments allow testing of the predictions of hydrocodes used in simulations of the interactions of high pressure shocks with matter. Such codes are utilized In the NNSA’s program for inertial fusion, for NNSA’s science programs, and for the simulations of supernovas.