In inertial confinement fusion (ICF), polycrystalline diamond—referred to as high density carbon (HDC)—has become a promising ablator candidate. However, with smaller grain size and lower initial density, the equation of state (EOS) for HDC can deviate from that for single-crystal diamond, which could be a concern for ICF designs, but current experimental EOS studies for HDC are far from sufficient to clarify how initial density affects target compressibility. Presented here are measurements of the Hugoniot for HDC with an initial density of 3.23 g/cm³ at pressures of 17–26 Mbar. Combined with experimental data reported for nanocrystalline diamond (NCD), a stiffer compressibility of NCD due to lower initial density is confirmed. Two porous models are used for comparison and seem to offer better agreement compared with SESAME databases. Also, the effect of temperature on the Grüneisen parameter, which is usually neglected, might need to be considered for NCD under these conditions. The present data offer important support for EOS studies relevant to ICF and constrain the construction of wide-range EOS.

Using the SG-III prototype laser at China Academy of Engineering Physics, Mianyang, we irradiated polystyrene (CH) samples with a thermal radiation drive, reaching conditions on the principal Hugoniot up to P ≈ 1 TPa (10 Mbar), and away from the Hugoniot up to P ≈ 300 GPa (3 Mbar). The response of each sample was measured with a velocity interferometry diagnostic to determine the material and shock velocity, and hence the conditions reached, and the reflectivity of the sample, from which changes in the conductivity can be inferred. By applying the self-impedance mismatch technique with the measured velocities, the pressure and density of thermodynamic points away from the principal Hugoniot were determined. Our results show an unexpectedly large reflectivity at the highest shock pressures, while the off-Hugoniot points agree with previous work suggesting that shock-compressed CH conductivity is primarily temperature-dependent.

The melting behavior of tantalum under high pressure is of fundamental importance to materials science and high-energy-density applications. In this study, we investigated tantalum up to 450 GPa by combining in situ x-ray diffraction with ab initio molecular dynamics (AIMD) simulations. Our experiments provide direct evidence that the body-centered cubic phase is retained from ambient conditions to 318 GPa. This conclusion is supported by the observation of multiple diffraction peaks, including Ta(110), Ta(200), and Ta(211). Our findings on the crystal structure are consistent with those reported by recent work [Phys. Rev. Lett. 126, 255701 (2021)]. The melting curve was derived from AIMD simulations based on density functional theory, without the use of empirical potentials. The obtained melting curve shows good agreement with earlier reliable first-principles theoretical studies, suggesting the limitations of empirical models over broad pressure and temperature ranges. Our combined experimental and computational approach provides a robust framework for studying high-pressure melting in refractory metals and is broadly applicable to materials subjected to extreme environments.

The thermodynamic properties of boron nitride under extreme pressures and temperatures are of great interest and importance for materials science and inertial confinement fusion physics, but they are poorly understood owing to the challenges of performing experiments and realizing ab initio calculations. Here, we report the first shock Hugoniot data on hexagonal boron nitride at pressures of 5–16 Mbar, using hohlraum-driven shock waves at the SGIII-p laser facility in China. Our density functional theory molecular dynamics calculations closely match experimental data, validating the equations of state for modeling the shock response of boron nitride and filling a crucial gap in the knowledge of boron nitride properties in the region of multi-Mbar pressures and eV temperatures. The results presented here provide fundamental insights into boron nitride under the extreme conditions relevant to inertial confinement fusion, hydrogen–boron fusion, and high-energy-density physics.

In indirect-drive inertial confinement fusion (ICF) research, the meticulous design and optimization of laser parameters are crucial for achieving high-gain ignition. The intensity of the toe laser, used for ablating the hohlraum sealing membrane, is a subtle but equally critical parameter. This study introduces a novel experimental approach using the Velocity Interferometer System for Any Reflector (VISAR) to assess the impact of toe laser intensity on the compression of fusion capsules. By tracking the reflectivity of tracer layers and shock velocities in liquid deuterium, the adverse effects of insufficient toe laser intensity on capsule compression have been unveiled for the first time. From a comparison with hydrodynamic simulations, we show that below a critical threshold of 0.23 × 10¹⁴ W cm⁻², the adiabat, a measure of the fuel’s compression efficiency, increases markedly with the toe laser intensity decreases, whereas it remains stable within the range of (0.23 ∼ 7) × 10¹⁴ W cm⁻². Our findings provide critical insights on toe laser parameter design, enhancing our understanding of the role of toe laser intensity in ICF experiments. This research not only refines the parameters for laser operation but also underscores the importance of precision in achieving the desired implosion efficiency, contributing to the development of nuclear fusion as a clean energy source.