VISAR for measuring equation of state and shock propagation in liquid deuterium (abstract).

Initial laser-driven equation of state (EOS) experiments on liquid deuterium employed x-ray radiography to track the shock and particle speeds in the shock compressed sample. With the high pressures available with laser drivers we found that it is also possible to track the shock front directly with a velocity interferometer system for any reflector (VISAR) because the shock front reflects light across the visible spectrum with reflectance around 50% for shocks stronger than 50 GPa in liquid deuterium. We have observed similar reflectances in other dielectric samples, such as diamond, LiF, and water. The pressure required to produce a reflecting shock varies with each material. This phenomenon allows us to design impedance-matched EOS experiments using velocity interferometry to measure the propagation speed in the transparent shocked materials, and step breakout measurements to determine the speed in the pusher. In a different kind of experiment we have observed double shock compression in liquid deuterium by impacting a shock in liquid deuterium at a LiF anvil placed in the liquid sample. VISAR can be used to track the shock in the deuterium as well as the motion of the deuterium–LiF interface subsequent to impact. This allows us to diagnose double-shock states using the VISAR technique. As a final example VISAR can be used to track shock overtake events such as produced by shaped pulse compression or shock reverberation effects in the accelerating pusher. This capability is directly applicable to shock timing experiments needed to tune the drive pulse for inertial confinement fusion capsules on the National Ignition Facility. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]