Laser driven shockless compression for extracting near-isentrope equation-of-state measurements

Laser produced x-ray drive was used to shocklessly compress solid Al to a peak longitudinal stress of 110 GPa within 10 ns. Interface velocities versus time for multiple Al thicknesses were measured and converted to stress-density (P$_{x}-\rho )$ for near isentrope conditions using an iterative Lagrangian analysis. These are the most rapid shockless compression P$_{x}{\rm o}(\rho ){\rm p}$ data ever reported. P$_{x}{\rm o}(\rho ){\rm p}$ are stiffer than expected from models that are benchmarked against both static and shock experiments, suggesting a larger than expected time dependent viscoelastic response. In addition, we present the first results of a laser driven dynamic loading technique used to map out phase boundaries in Bismuth over ultra fast compression rates. Multi-grain Bi foils 20$\mu $m thick were shocklessly loaded to peak stresses of $\sim $11 GPa over 30ns. This time dependent compression causes the Bi sample to traverse several phase boundaries (I$\to $IV, Liquid) during a single shot. A time resolved velocity interferometer is used to measure the effects of new phases on a transmitted wave velocity profile. Ramp compression over several nanoseconds with initial temperatures spanning 410K to 521K results in over-driving of the Bi I-Liquid equilibrium phase boundary. A Bi multi-phase equation-of-state (EOS) for Bi I$\to $IV and Liquid together with a kinetics model give insights into the transition rates for different phase transitions.