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A new method for shockless compression and acceleration of solid materials is presented. A plasma reservoir pressurized by a laser-driven shock unloads across a vacuum gap and piles up against an Al sample thus providing the drive. The rear surface velocity of the Al was measured with a line VISAR, and used to infer load histories. These peaked between approximately 0.14 and 0.5 Mbar with strain rates approximately 10(6)-10(8) s(-1). Detailed simulations suggest that apart from surface layers the samples can remain close to the room temperature isentrope. The experiments, analysis, and future prospects are discussed.

Experiments conducted on the Omega laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] and simulations show reduced Richtmyer–Meshkov growth rates in a strongly shocked system with initial amplitudes kη0⩽0.9. The growth rate at early time is less than half the impulsive model prediction, rising at later time to near the impulsive prediction. An analytical model that accounts for shock proximity agrees with the results.

In ongoing experiments performed on the OMEGA laser [J. M. Soures et al., Phys. Plasmas 5, 2108 (1996)] at the University of Rochester Laboratory for Laser Energetics, nanosecond laser pulses are used to drive strong blast waves into two-layer targets. Perturbations on the interface between the two materials are unstable to the Richtmyer–Meshkov instability as a result of shock transit and the Rayleigh–Taylor instability during the deceleration-phase behind the shock front. These experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen–helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. The authors are, at present, particularly interested in the development of the Rayleigh–Taylor instability through the late nonlinear stage, the transition to turbulence, and the subsequent transport of material within the turbulent region. In this paper, the results of numerical simulations of two-dimensional (2D) single and multimode experiments are presented. These simulations are run using the 2D Arbitrary Lagrangian Eulerian radiation hydrodynamics code CALE [R. T. Barton, Numerical Astrophysics (Jones and Bartlett, Boston, 1985)]. The simulation results are shown to compare well with experimental radiography. A buoyancy-drag model captures the behavior of the single-mode interface, but gives only partial agreement in the multimode cases. The Richtmyer–Meshkov and target decompression contributions to the perturbation growth are both estimated and shown to be significant. Significant dependence of the simulation results on the material equation of state is demonstrated, and the prospect of continuing the experiments to conclusively demonstrate the transition to turbulence is discussed.

Strain-induced disorder, phase transformations, and transformation-induced plasticity in hexagonal boron nitride under compression and shear in a rotational diamond anvil cell: In situ x-ray diffraction study and modeling Iron was ramp-compressed over timescales of 3 t(ns) 300 to study the time-dependence of the a!e (bcc!hcp) phase transformation. Onset stresses r a!e ð Þ for the transformation $14.8-38.4 GPa were determined through laser and magnetic ramp-compression techniques where the transition strain-rate was varied between 10 6 _ l a!e (s À1 ) 5Â10 8 . We find r a!e ¼ 10.8 þ 0.55 ln _ l a!e ð Þ for _ l a!e < 10 6 /s and r a!e ¼ 1.15 _ l a!e ð Þ 0:18 for _ l a!e > 10 6 /s. This _ l response is quite similar to recent results on incipient plasticity in Fe [Smith et al., J. Appl. Phys. 110, 123515 (2011)] suggesting that under high rate ramp compression the a ! e phase transition and plastic deformation occur through similar mechanisms, e.g., the rate limiting step for _ l > 10 6 /s is due to phonon scattering from defects moving to relieve strain. We show that over-pressurization of equilibrium phase boundaries is a common feature exhibited under high strain-rate compression of many materials encompassing many orders of magnitude of strain-rate. V C 2013 AIP Publishing LLC.