The 5th International Conference on Matter and Radiation at Extremes (ICMRE 2020)

37 / 2020-02-18 15:33:32

Thermodynamic state and optical reflectivity of hydrocarbons under double-shocked state

reflectivity,hydrocarbon,double shock,metallization

Plenary track > High Energy Density Physics

As one of the most abundant chemical compounds throughout the Universe, the behavior of hydrocarbons (CH) at extreme pressures and temperatures is of great interest in the field of high energy density physics and planetary science. The compression characteristics of CH, such as conductivity and compressibility, serve as important benchmarks for exploring the interior structure of icy giant planets such as Neptune and Uranus. The interior of these icy giants is expected to have lower temperature compared with single shock. These off-Hugoniot states could be achieved in laboratory by double-shock or isentropic compression with wider parameter range. Furthermore, in the inertial confinement fusion (ICF) research, CH is considered as promising ablator candidates due to its high ablation rate and mature technology. It is used to convert energy from laser and X-rays to kinetic energy of the imploding Deuterium-tritium capsule by multiple precisely tuned shocks. This topic simultaneously raises an imminent demand for their off-Hugoniot properties. Compared to extensive studies on CH Hugoniot experiment, the off-Hugoniot data and experiments need to be explored further.
In this study, off-Hugoniot state of polystyrene (PS) is driven by a hohlraum with shaped pulse at SG-Ⅲ prototype lasers. Double shocked PS with a pressure of ~300 GPa and temperature of ~1.2eV is accessed with VISAR measurement, i.e., shock velocity and reflectivity. Pressure and density are determined by self-impedance match method, while temperature is estimated by hydrodynamic simulation. These parameters on and off the principle CH Hugoniot are analyzed. Our results show reflectivity shares similar relationship for both single shock and double shocked targets. This may indicate the metallization of CH at the shock front is primarily temperature dependent. The study might drop a hint of how phase separation process at extreme pressures and provides additional measurement from macroscopic point of view. It could also be helpful for understanding of thermodynamic behavior of hydrocarbons under high pressures.