Shock-wave experiments at threefold compression

Abstract

A high-pressure shock wave generated by an underground nuclear explosion was used to obtain precise Hugoniot data from impedance-matching measurements at pressures ranging from 1 to 6 TPa and corresponding to threefold compressions. The shock passed from a 180-mm-diam by 17.5-mm-thick lead driver into a 12-mm-thick molybdenum base plate and then into a central 12-mm-thick $^{238}\mathrm{U}$ sample surrounded by stacks of the following pairs of 10-mm-thick samples (lower sample first): Mo-Pu ($\ensuremath{\delta}$ phase), W-Pb, A1-porous Mo (19% porosity), C-LiH, Cu-Au, and Fequartz (crystalline). Shock-front arrival-time measurements with 80 electrical-contact pins embedded in the assembly were used to determine shock velocities with uncertainties of 1.4-2.6%; the shock front was found to be slightly curved (with a radius of curvature of \ensuremath{\sim}2 m) but symmetric about the axis of the cylindrical driver with an upper limit on tilt asymmetry of 1.5 mrad. The measured shock velocity of 30.60 km/s in the molybdenum base plate corresponds to a pressure of 6.43 TPa based on the improved sesame equation of state (EOS) for molybdenum. Impedancematching analysis using the molybdenum base plate as the standard or reference material for the lower samples and using the lower samples as standards for the upper materials gave the following Hugoniot points in pressure ($P$) particle-velocity ($u$) coordinates for the indicated sample materials: A1($P=2.93$ TPa, $u=27.57$ km/s), porous Mo(4.65, 19.99), C(2.64, 28.38), LiH(1.225, 35.52), Cu(6.06, 21.15), Fe(5.71, 21.73), and quartz(2.75, 26.76). For the porous molybdenum sample, the calculated Hugoniot based on the sesame EOS barely lies within the region of uncertainty around the measured point. For the other samples, the calculated Hugoniots are in good agreement with the measured points.