Zanyang Guan

The design of inertial confinement fusion implosions relies on the predictable control of shock dynamics, where the first-shock strength is conventionally governed by the initial laser picket intensity. Here, using shock timing experiments at the SG 100 kJ laser facility, we report a distinct deviation from this conventional scaling: when a high-power main pulse precedes shock breakout, the first-shock velocity in liquid deuterium decreases with increasing picket drive. We attribute this anomaly to preheating of the ablator by high-energy X rays from the early main pulse. Integrated simulations and theory reveal that this preheating induces a rapid pressure rise at the ablator fuel interface. The resulting enhanced pressure overrides the picket driven dynamics during shock impedance matching, accelerating the shock into the fuel and thus inverting the expected scaling. Our findings establish a pressure-dominated mechanism that revises the framework for shock tuning in preheat-affected implosions and provides direct guidance for pulse shaping in future high-energy-drive designs.

Laser-driven inertial confinement fusion (ICF) is a crucial frontier for future fusion energy utilization. Shock wave velocity diagnosis is critical for investigating implosion instability in laser-driven ICF. The conventional imaging velocity interferometer system for any reflector (VISAR) and two-dimensional VISAR techniques only obtain one-dimensional high-temporal-resolution velocity evolution or two-dimensional shock wave information at a specific time. The compressed ultrafast photography (CUP)–VISAR (CUP-VISAR) system enables high spatiotemporal resolution measurement of continuous two-dimensional velocity fields by combining hardware compressive sampling and software reconstruction, but velocity field reconstruction quality and accuracy remain challenging. This paper proposes a CUP-VISAR fringe reconstruction method based on plug-and-play dual-channel deep image priors, which achieves high-quality reconstruction without training data. Experimental results demonstrate that the maximum error of velocity field inversion is less than 2%, which is comparable to the accuracy of Line-VISAR. By virtue of only a single-shot experiment, the combination of the CUP-VISAR system and the proposed algorithm enables the inversion and acquisition of high-precision continuous two-dimensional shock wave velocity fields, which provides accurate and comprehensive data support for the investigation of fusion ablation symmetry and hydrodynamic instabilities in ICF experiments.

On laser facilities for achieving inertial confinement fusion ignition, several beams are usually bundled together and injected into the target chamber through a common port. This specific configuration could lead to laser–plasma interaction (LPI) processes that are quite different from those of a single laser beam, as well as to more options for suppressing LPI via combination of different laser smoothing techniques on the beams in a bundle. For studying LPI of a bundle of beams, a novel facility named Shenguang Octopus has been developed. Recently, the first LPI experiments have been performed by axially irradiating a gas-filled glass pipe or a gold hohlraum target with the bundled eight laser beams at an overlapped intensity of ∼1×1015W/cm2, producing ∼5-mm-long homogeneous plasmas with densities of ∼3×1020cm−3 and temperatures of 1.2–1.5 keV. Efficient laser propagation without plasma filamentation and beam spraying has been observed via side-on X-ray images of glass pipe targets. Results from the gold hohlraum targets indicate that single-beam backward stimulated Brillouin scattering (SBS) and multibeam seeded side-SBS play major roles in the interaction, while other multibeam LPI processes expected before the experiments are not observed. Several beam smoothing techniques, such as mixed polarizations, smoothing by spectral dispersion, and multicolor mode, are demonstrated to be effective in suppressing LPI under current conditions.

Laser-driven inertial confinement fusion (ICF) is an important experimental platform for high-energy-density physics research under extreme conditions. In ICF research, high-quality shock waves are key to fusion energy release. The velocity interferometer system for any reflector (VISAR) is the most important diagnostic technique for measuring quantities such as shock wave and particle velocities with high precision and high spatiotemporal resolution. This paper provides a detailed introduction to the various configurations of VISAR on 10 and 100 kJ-level laser facilities in China, including Line VISAR, Dual-Axis VISAR, Wide-Angle VISAR, and Compressed Ultrafast Photography-VISAR. Recent advances and applications of VISAR diagnostics at these laser facilities are presented, and the future trend of development of high-spatiotemporal-resolution velocity diagnostic technology is described.

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.

The first laser–plasma interaction experiment using lasers of eight beams grouped into one octad has been conducted on the Shenguang Octopus facility. Although each beam intensity is below its individual threshold for stimulated Brillouin backscattering (SBS), collective behaviors are excited to enhance the octad SBS. In particular, when two-color/cone lasers with wavelength separation 0.3 nm are used, the backward SBS reflectivities show novel behavior in which beams of longer wavelength achieve higher SBS gain. This property of SBS can be attributed to the rotation of the wave vectors of common ion acoustic waves due to the competition of detunings between geometrical angle and wavelength separation. This mechanism is confirmed using massively parallel supercomputer simulations with the three-dimensional laser–plasma interaction code LAP3D.

One-dimensional line velocity interferometer system for any reflectors (VISARs) acts as a significant diagnostic device in the process of the inertial confinement fusion, which can be used to measure the free surface velocity and the history of shockwave velocity in transparent media over time. But the lack of spatial information makes it impossible to measure the flatness of wavefront. The compressed ultrafast photography (CUP) system developed in recent years can realize two-dimensional ultrafast photography. We have designed a new two-dimensional VISAR diagnosis system by combining the CUP with line-VISAR, called the CUP-VISAR, which will be of great significance in two-dimensional shockwave front measurement. In this paper, a data simulation method of CUP-VISAR is proposed to study the length of diagnostic time window of the device. A series of original VIASR images are firstly generated and then the compressed images are simulated after image encoding and compression. Finally, two-step iterative shrinkage thresholding algorithm is used to reconstruct the compressed images, which results in corresponding reconstructed images. In order to verify the restoration effect of the algorithm, we calculate the velocity error and image correlation coefficient value. Finally the relationship between the image reconstruction quality and the number of images is preliminarily obtained, which provides reference for the actual experiment.