Measurements of the principal Hugoniots of dense gaseous deuterium−helium mixtures: Combined multi-channel optical pyrometry, velocity interferometry, and streak optical pyrometry measurements

Abstract

The accurate hydrodynamic description of an event or system that addresses the equations of state, phase transitions, dissociations, ionizations, and compressions, determines how materials respond to a wide range of physical environments. To understand dense matter behavior in extreme conditions requires the continual development of diagnostic methods for accurate measurements of the physical parameters. Here, we present a comprehensive diagnostic technique that comprises optical pyrometry, velocity interferometry, and time-resolved spectroscopy. This technique was applied to shock compression experiments of dense gaseous deuterium–helium mixtures driven via a two-stage light gas gun. The advantage of this approach lies in providing measurements of multiple physical parameters in a single experiment, such as light radiation histories, particle velocity profiles, and time-resolved spectra, which enables simultaneous measurements of shock velocity, particle velocity, pressure, density, and temperature and expands understanding of dense high pressure shock situations. The combination of multiple diagnostics also allows different experimental observables to be measured and cross-checked. Additionally, it implements an accurate measurement of the principal Hugoniots of deuterium−helium mixtures, which provides a benchmark for the impedance matching measurement technique.

Diagnostics and Production of Warm Dense Matter with Multishock Reverberation Compression Technique

“…Before shock compression, the gaseous sample was precompressed to a dense state with a pressure of around 20−40 MPa from ambient conditions by pressurization devices to gain high initial density. The initial density ρ 0 of dense gas sample was measured to an accuracy of 0.2% by a draining method used in our previous work [32]. The composite window is the most important part of the target, which consists of one layer of ~4.0 mm thick lithium fluoride (LiF) and one layer of ~2.0 mm thick sapphire (Al 2 O 3 ) behind the LiF to prevent precompression fracturing.…”

“…In this case, DPS-I measures both the apparent particle velocity U p,1 and shock velocity U s,1 , which can be corrected according to the refractivity of initial gas sample for 1550 nm [32]. Figure 4 shows a typical experimental record for this situation, which was obtained from the multi-shock compression experiments for the deuterium-helium mixture with a pressure of ~40 MPa and an ambient temperature, driven by a 5.52 km/s Ta flyer.…”

“…We applied the above mention diagnostic technique and method to perform the experiments on warm dense H 2 , D 2 , He [33], H 2 +He [26], D 2 +He [32], Ne, Ar [34,35], and Xe [36,37] over several MPa to Mbar pressure region. The two-, four-, six-, and ten-shock in Xe, Ar, Ne, and low-Z gas (H 2 , D 2 , He, H 2 +He, D 2 +He) reverberate back and forth between the two high shock impedance of base-plate and window was directly observed in our experiments.…”