Optimization of loading pressure waveforms for piston driven isentropic compression

Abstract

Smooth ramp loading with higher pressure amplitude is usually preferred in the isentropic compression experiment (ICE) of condensed materials. Optimizing the pressure waveforms of ICE is important in avoiding any shock wave propagating during ramp loading and raising the peak pressure as high as possible. Most reports on shaping ICE waveforms mainly focused on magnetohydrodynamic numerical simulations; a few used the hydrodynamic theory of isentropic flow. However, some points can be improved. Based on one-dimensional planar isentropic flow theory and regarding the ICE loading pressure exerted on the sample's surface as a time-dependent piston boundary condition, a condition for the ramp-to-shock transition as a compression wave propagates in the sample materials, has been derived that forms a necessary condition to avoid such transitions and determines ICE loading pressure waveforms with shorter rise time. A comparison of results is presented for samples of the maximum thickness and for optimized current waveforms obtained in magnetically driven ICEs.