Simultaneous VISAR and TXD Measurements on Shocks in Beryllium Crystals

Shock waves were induced in single crystals of beryllium, by direct illumination using the TRIDENT laser at Los Alamos. The velocity history at the surface was measured using a line‐imaging VISAR, and transient X‐ray diffraction (TXD) records were obtained with a plasma backlighter and X‐ray streak cameras. At lower pressures, the VISAR records exhibited an elastic precursor followed by a plastic wave and spall. At higher pressure, the velocity records showed a two‐wave structure suggesting a phase change, then at the highest pressure a single broad wave suggesting a shock directly into the high pressure phase. The rocking curves of the crystals were typically about 2 degrees wide, so analysis of the TXD records is complicated by the relatively large amount of blurring. However, the Bragg record of the shocked 0002 peak clearly indicates a smaller lattice parameter at higher pressure. In the shots where polymorphism seemed to appear in the VISAR record, additional lines appeared in the Bragg record, and n...