Principal Hugoniot, reverberating wave, and mechanical reshock measurements of liquid deuterium to 400 GPa using plate impact techniques

Abstract

The high-pressure response of cryogenic liquid deuterium $(L{\mathrm{D}}_{2})$ has been studied to pressures of $\ensuremath{\sim}400\mathrm{GPa}$ and densities of $\ensuremath{\sim}1.5{\mathrm{g}/\mathrm{c}\mathrm{m}}^{3}.$ Using intense magnetic pressure produced by the Sandia National Laboratories $Z$ accelerator, macroscopic aluminum or titanium flyer plates, several mm in lateral dimensions and a few hundred microns in thickness, have been launched to velocities in excess of 22 km/s, producing constant pressure drive times of approximately 30 ns in plate impact, shock wave experiments. This flyer plate technique was used to perform shock wave experiments on $L{\mathrm{D}}_{2}$ to examine its high-pressure equation of state. Using an impedance matching method, Hugoniot measurements of $L{\mathrm{D}}_{2}$ were obtained in the pressure range of $\ensuremath{\sim}22--100\mathrm{GPa}.$ Results of these experiments indicate a peak compression ratio of approximately 4.3 on the Hugoniot. In contrast, previously reported Hugoniot states inferred from laser-driven experiments indicate a peak compression ratio of approximately 5.5--6 in this same pressure range. The stiff Hugoniot response observed in the present impedance matching experiments was confirmed in simultaneous, independent measurements of the relative transit times of shock waves reverberating within the sample cell, between the front aluminum drive plate and the rear sapphire window. The relative timing was found to be sensitive to the density compression along the principal Hugoniot. Finally, mechanical reshock measurements of $L{\mathrm{D}}_{2}$ using sapphire, aluminum, and \ensuremath{\alpha}-quartz anvils were made. These results also indicate a stiff response, in agreement with the Hugoniot and reverberating wave measurements. Using simple model-independent arguments based on wave propagation, the principal Hugoniot, reverberating wave, and sapphire anvil reshock measurements are shown to be internally self-consistent, making a strong case for a Hugoniot response with a maximum compression ratio of $\ensuremath{\sim}4.3--4.5.$ The trends observed in the present data are in very good agreement with several ab initio models and a recent chemical picture model for $L{\mathrm{D}}_{2},$ but in disagreement with previously reported laser-driven shock results. Due to this disagreement, significant emphasis is placed on the discussion of uncertainties, and the potential systematic errors associated with each measurement.