High-Pressure Isentropic Compression Experiments on the Sandiaz Accelerator

Summary form only given. A capability to produce quasi-isentropic compression of solids using pulsed magnetic loading on the Sandia Z accelerator has recently been developed and demonstrated. The accelerator is capable of producing >20 MA current pulses with ~300 ns rise-time into a short circuit load, generating intense magnetic fields within the anode cathode (AK) gap. With proper design of the short circuit load and suitable shaping of the current pulse, this technique allows planar, continuous compression of materials several hundred microns in thickness to stresses approaching 350 GPa. Development of a loading capability for direct measurement of material properties along an isentrope has been a long standing goal in the equation of state (EOS) community. Combined with more traditional Hugoniot compression data, the principal isentrope provides a more comprehensive description of the complete EOS. Furthermore, direct measurement of the isentrope, which lies very close to the room temperature isotherm, has the potential to improve the accuracy of pressure standards used to calibrate pressure scales in static high-pressure diamond anvil cell experiments. Isentropic compression experiments (ICE) are also well suited for the study of pressure induced phase transformations in materials. Since the loading path followed in the experiment is the material isentrope, even relatively small volume change transitions, which might be extremely difficult to probe in shock wave experiments, are readily observed. Furthermore, due to the low temperature increase associated with isentropic compression it is possible to study the kinetics of rapid solidification. Examples of such experiments will be discussed. As a final example, the use of ICE techniques to infer material strength at high pressures and densities will be discussed. Comparison of the loading and subsequent unloading wave profiles in a material provides a means to directly infer the strength of the material at pressure. Feasibility experiments performed on aluminum to stresses of ~150 GPa will be presented