P2 is the remaining principal asymmetry in laser-driven hohlraums. A simple analytic model for P2 asymmetry on the Shenguang 100 kJ laser facility is presented, which is based on hohlraum geometry, wall albedo, plasma expansion, and shell velocity. The calculated P2 asymmetry from the model is in reasonably good agreement with experimental data from pre-pulse, shell flight and stagnation stages. The P2 model appears to capture the essential physics governing drive symmetry and has been implemented to guide new symmetric implosion designs, enabling a more rapid convergence to a symmetric implosion than the conventional trial-and-error approach.

Collective Thomson scattering (CTS) is crucial for inertial confinement fusion (ICF) hohlraum diagnostics, but measurement of the electron plasma wave (EPW) feature remains challenging. The conventional collisionless model suffers from two critical defects: under low-temperature, high-density conditions it predicts an extremely narrow EPW peak that causes numerical sampling distortion, and it predicts a monotonic increase of peak intensity with decreasing scattering angle, which would mislead experimental design. To overcome these issues, the Bhatnagar–Gross–Krook (BGK) collisional model is introduced. The BGK model predicts a nonmonotonic peak intensity with an optimal angle between 30° and 60°, and yields a finite, resolvable peak width that eliminates sampling artifacts. It also enables reliable assessment of drive-beam backgrounds. Guided by the predicted optimal angle, CTS experiments at 42° were performed on the Shenguang-100 kJ facility. For the first time, both ion and electron features were simultaneously measured in the hohlraum corona, with the electron signal clearly distinguishable from the background. Joint fitting provides the temporal evolution of electron density and temperature. This work establishes a unified, collision-corrected diagnostic framework that overcomes a long-standing obstacle to measuring electron density and temperature in ICF hohlraum plasmas.

Detailed investigation of the x-ray drive on the capsule at the center of the hohlraum is crucial to solve the "drive deficit" problem in inertial confinement fusion. A pioneering work for probing the drive flux at the hohlraum center by simultaneously measuring the re-emitted flux and shock velocity was reported [X. Xie et al., Phys. Rev. Lett. 128, 075001 (2022)0031-900710.1103/PhysRevLett.128.075001]. However, in the last experiment only two discrete shock velocity values can be obtained, as the streaked optical pyrometer was employed. In this work, we present characterization of the time-dependent x-ray drive on the capsule by simultaneously measuring the time-dependent localized re-emitted flux and the time-dependent shock velocity. The time-dependent localized re-emitted flux was measured by the space-resolving flux detector, while the time-dependent shock velocity was obtained with the velocity interferometer system for any reflector. Two-dimensional radiation hydrodynamic simulations revealed that the time history of the re-emitted flux as well as the shock velocity can be well reproduced. This technique presented a way for the determination of the x-ray drive at the center of the cylindrical hohlraum as well as other novel hohlraums.

The BC8 phase of carbon was theoretically proposed nearly 40 years ago but lacking direct experimental structural confirmation, leaving its high-pressure stability and the predicted diamond-BC8-liquid triple point unresolved. Constraining carbon’s terapascal phase diagram is important for planetary interiors and inertial confinement fusion. Here, we report decaying shock compression experiments on single-crystal diamond with [100] orientation up to 1600 GPa and 14000 K, supported by large-scale molecular dynamics simulations using a machine-learning interatomic potential. Reflectivity increases markedly from 600 GPa and 6000 K, indicating formation of a metastable liquid-like intermediate (MLI). The measured Hugoniot curve closely follows the negative slope of the diamond melting curve between 700 and 830 GPa, is compatible with a diamond-BC8-liquid triple point at approximately 830 GPa and 7200 K, and is consistent with the BC8 melting curve from 830 to 1000 GPa. These measurements provide the high-accuracy thermodynamic constraints for testing melting curve models near the predicted tripe point and support the existence of the predicted BC8 phase of carbon. Simulations suggest that the MLI provides a transient pathway associated with the diamond-to-BC8 transition. These findings provide unprecedented experimental thermodynamic constraints on carbon's high-pressure phase diagram, offer new insights into ultrafast phase transitions in condensed matter at terapascal pressures, and suggest that carbon may contribute to magnetic-field generation within carbon-rich exoplanets. Direct structural confirmation of BC8 through in situ X-ray diffraction remains an open challenge.

In indirect-drive inertial confinement fusion (ICF), the radiation drive temperature of the hohlraum is related to the shock velocity and implosion velocity of the capsule. The radiation drive symmetry on the capsule is the vital parameter for the hotspot symmetry. A new method is proposed to simultaneously determine the radiation temperature and P2 asymmetry on the capsule by measuring the re-emitted x-ray radiation flux along two orthogonal directions. The interaction between the hohlraum and the imploded capsule can be decoupled by employing a high-Z substitute capsule. The effects of opacity and equation of state on the measurement of the P2 asymmetry are given based on the self-similarity theory. The demonstration experiments were conducted on the Shenguang-100 kJ laser facility. The evolutions of the radiation drive temperature and P2 asymmetry are obtained in the experiment. The impact of diagnostic holes and laser beam absences on the P2 asymmetry is quantitatively evaluated with the view-factor calculation. The temporal trend of the symmetry is consistent between the experiment and the integrated simulation (LARED-JC). However, the experimental symmetry differs from the simulation results from the middle of the main pulse. This might be caused by the inverse bremsstrahlung absorption or the crossed-beam energy transfer (CBET) process. The new method can provide both radiation drive temperature and P2 asymmetry for different hohlraumsin experiments. It enables time-resolved determination of both the laser power multiplier and the cone fraction multiplier, which is beneficial for optimizing the innovative hohlraum designs.

Backscattering due to laser plasma instabilities (LPIs) presents a risk in the laser-driven inertial confinement fusion. Generally, it is assumed that the backscattering of laser beams in the same cone is identical in hohlraum physics studies. In the experiments performed at SG-100kJ laser facility, we find that the backscattering of laser beams in the same cone are quite different. Our investigation reveals the main reason for this phenomenon is that the laser beams in the same cone obtain different power from their neighbor beams via crossed-beam energy transfer (CBET) depending on their polarizations. The dependence of multi-beam CBET on laser polarization arrangement is confirmed in a specially designed experiment. These findings are crucial for understanding the backscattering, CBET, energy deficit and the azimuthal drive asymmetry in cylindrical hohlraums.

The first experiments on laser-driven cylindrical gold foam hohlraums have been performed at the 100 kJ SG-III laser facility. Measurements of the expanding plasma emission show that there is less expanding plasma fill in foam hohlraums with a wall density of 0.8 g/cm3 than in solid gold hohlraums. The radiation temperatures at different angles confirm these results. Simulation results show that the expanding plasma density in the foam hohlraums is lower than in the solid hohlraums, resulting in less expanding plasma emission and higher radiation temperature. Thus, foam gold hohlraums have advantages in reducing wall plasma filling and improving X-ray transmission, which has potential applications in achieving a higher fusion yield.

The influence of unwanted X-ray background as well as the variation of the physical condition for radiation temperature (Tr) measurement is investigated in this work. Laser clipping by LEH, residual unconverted light striking target support structures and laser energy deposited on the CH membranes will lead to an overestimation of the hohlraum Tr. Laser pointing accuracy and laser power imbalance change the fraction of certain laser spots as well as their energy in the sight of view, causing a deviation in estimating the hohlraum Tr. Besides, LEH closure will lead to an underestimation of the hohlraum Tr.

Early hot electron can preheat the pellet fuel and thus lead to lower implosion performance. The properties of hot electrons in early stage of implosion experiments in Shenguang-100 kJ laser facility were investigated. It was shown that both the temperature and the energy of early hot electrons were very low. The upper limit of the temperature and the energy of early hot electrons in our experiments were only 7.7 keV and 0.35 J, respectively. Besides, the generation mechanisms of early hot electrons were also different from NIF experiments according to the results of the hard X-ray imager (HXI). In NIF experiments, two-plasmon decay and multi-beam stimulated Raman scattering (SRS) were dominate mechanisms that generate early hot electrons. However, SRS of the outer beams was our dominant mechanism. Spectrum of the scattered light of SRS was obtained by radiative hydrodynamic and ray-tracing simulations. The result showed that the spectrum was peaked at λ _s=482 nm , which meant hot electrons with the temperature near 7keV can be generated. And from the result of HXI, hot electrons deposited onto the pellet were estimated to less than 6.8× 10^-3 J. Deeper analysis showed that, in the beam overlapping region, the plasma density was unsuitable for multi-beam SRS, so no hot electrons with larger temperature were generated.

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.

An experiment on 100 kJ laser facility is performed to study the motive features and radiation properties of plasmas from different areas inside gas-filled cylindrical hohlraums. These hohlraums are designed to possess one open end and one laser entrance hole (LEH) with different diameters, which would or not result in the blocking of the LEH. An x-ray streak camera that is set at 16 degrees with respect to the hohlraum axis is applied to acquire the time-resolved x-ray images from the open end. Based on the images, we can study the evolutions of the wall plasma, corona bubble plasma and LEH plasma simultaneously through an equivalent view field of hohlraum interior. Multi-group flat response x-ray detectors are applied to measure the x-ray fluxes. In order to understand these characteristics, our two-dimensional radiation hydrodynamic code is used to simulate the experimental results. For the accuracy of reproduction, dielectronic recombination and two parameter corrections are applied in our code. Based on the comparison between experiments and simulations, we quantitatively understand the blocking process of LEH and the motion effects of other plasmas. The calibrated code is beneficial to design the gas-filled hohlraum in a nearby parameter space, especially the limit size of LEH.

The investigation of iron under high pressure and temperatures is crucial to understand the Earth’s core structure and composition and the generation of magnetic fields. Here, we present new in situ XRD measurements for iron in an off-Hugoniot state by laser-driven ramp compression at pressure of 200–238 GPa. The lattice parameters for the hexagonal (hcp)-Fe phase and the c/a ratios were obtained to compare them with previous static and dynamical data, which provides the direct confirmation of such parameters via the different compression paths and strain rates. This work indicates that laser ramp compression can be utilized to provide crystal structure information and direct key information on the crystal structure of Fe at the ultrahigh pressure–temperature conditions relevant for planetology.

In an experiment performed on the Shenguang-III prototype laser facility, collective Thomson scattering (TS) is used to study the spatial growth of stimulated Brillouin scattering (SBS) in a gas-filled hohlraum by detecting the SBS-driven ion acoustic wave. High-quality time-resolved SBS and TS spectra are obtained simultaneously in the experiment, and these are analyzed by a steady-state code based on the ray-tracing model. The analysis indicates that ion–ion collisions may play an important role in suppressing SBS growth in the Au plasma; as a result, the SBS excited in the filled gas region is dominant. In the early phase of the laser pulse, SBS originates primarily from the high-density plasma at the edges of the interaction beam channel, which is piled up by the heating of the interaction beam. Throughout the duration of the laser pulse, the presence of the TS probe beam might mitigate SBS by perturbing the density distribution around the region overlapping with the interaction beam.

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.

The novel octahedral spherical hohlraum can provide an ideal and practical approach for the next generation of laser systems to support both direct and indirect drive to achieve predictable and reproducible fusion gain via multiple schemes. To demonstrate its advantage in a naturally high symmetry at a cylindrically configured laser facility, it requires to repoint the laser beams to approach as close as possible the ideal octahedral beam configuration with an injection angle (the angle between a beam and the normal direction of its laser entrance hole (LEH)) ranging from 50° to 60°. We report our investigation and experiment on the optimum repointing scheme at the SGIII facility, which uses 32 beams, with 8 beams entering each polar LEH at 49.5° and 55°, and 4 beams entering each equatorial LEH at 61.5° and 62.1°. It contains residual imbalance between the polar and equatorial beams, leading to an asymmetry dominated by the spherical harmonic Y20 mode, which can be remarkably reduced by the stronger backscatters of equatorial beams. Our experiment demonstrated the feasibility of the 32-beam optimum repointing scheme and generation of 175 eV under 86 kJ inside a 2.4-mm-radius octahedral hohlraum with 0.7-mm-radius LEHs, which provided a strong support for the later experiment on proof-of-concept of octahedral spherical hohlraum [Lan et al., Phys. Rev. Lett. 127, 245001 (2021)]. 2D simulations on LEH closure agree well with the observations. This work opens a novel way of realization of a quasi-spherical irradiation at a cylindrically configured laser facility without supplementary symmetry control.

Both direct and indirect drive concepts of inertial confinement fusion rely on targets with cryogenic thermonuclear fuel shells for ignition. Experiments on the Shenguang-III prototype laser facility using laser-driven gas-filled hohlraums show distinct differences between cryogenic (20 K) and warm hohlraums. Although the measured x-ray flux in the photon range from 1.6 to 4.4 keV (Au M-band) is identical between cryogenic and warm hohlraums, the cryogenic hohlraum has a much slower rate of rise and is 20% lower in peak intensity of x-ray flux in the photon range from 0.1 to 4 keV. The reasons for this drive deficit between cryogenic and warm hohlraums are investigated using a similar series of hohlraum experiments. The experiments employ three types of hohlraums to distinguish the effect of a shroud window membrane and condensates. Warm hohlraums with a shroud window membrane replicate the slower rate of rise of radiation flux of cryogenic targets. When the shroud window is present, the measured x-ray flux in the hohlraum shows a drive deficit that decreases with time. However, the measured deficit increases as the viewing angle increases. All of these results indicate that the portion of the shroud not illuminated by the lasers absorbs the outgoing x-ray flux from the hohlraum.

The two-plasmon decay (TPD) instability of the backscattered light of the simulated Raman scattering (SRS) is first investigated with the help of one-dimensional (1D) and two-dimensional (2D) particle-in-cell (PIC) simulations. The 2D PIC simulation results show that the backscattered light of the SRS does excite TPD instability. Further, the comparison between 1D and 2D PIC simulation results shows that the backward SRS is suppressed by the excitation of TPD instability, which means the TPD instability of the scattered light could be a saturation scheme of SRS. It is also shown that, after the excitation of TPD, the electrons could experience a two-stage or even three-stage acceleration and their energy may reach to or even exceed 100 KeV, which means the TPD instability of the backscattered light could be a source of super-hot electrons.

We present for the first time characterization of the time-dependent radiation drive on the capsule by measuring the localized re-emitted flux at Shenguang-III prototype laser facility. The drive flux was obtained with measured re-emitted flux from the capsule and radiation fluxes from the hohlraum wall, in combination with radiation hydrodynamic simulations. It revealed that the temporal behavior of the drive flux was quite distinguished from the radiation flux from the hohlraum wall, and the drive flux was approximately 6 eV (12 eV) lower than the measured flux at up 55° (up 30°). This technique presents a novel way for the assessment of the drive flux, both in cylindrical hohlraums and novel hohlraums with more than two laser entrance holes. Pre-processed radiation hydrodynamic simulations indicate that this technique can also be applied in integrated implosion experiments utilizing standard fusion capsule with carbon-hydrogen ablators.

A new method for measuring the time-dependent drive flux at the hohlraum center is proposed as a better alternative to conventional wall-based techniques. The drive flux here is obtained by simultaneous measurement of the reemitted flux and shock velocity from a three-layered "cakelike" sample. With these two independent observables, the influence induced by the uncertainty of the material parameters of the sample can be effectively decreased. The influence from the closure of the laser entrance hole, which was the main challenge in conventional wall-based techniques, was avoided through localized reemitted flux measurement, facilitating drive flux measurement throughout the entire time history. These studies pave a new way for probing the time-dependent drive flux, for both cylindrical hohlraums and novel hohlraums with six laser entrance holes.

Based on the experimental conditions of the Shenguang-100 kJ laser facility, the feasibility and applicability of the deep ultraviolet quintuple-frequency Thomson scattering diagnostics are evaluated, and compared with the widely used quadruple-frequency Thomson scattering, so as to provide a reference for the technical route for high-precision diagnosis of inertial confinement fusion plasmas. The probe beam signal, the drive-beam background, and the bremsstrahlung background are evaluated, and the measurement bands of the Thomson scattering ion spectrum and electron spectrum are discussed respectively. The results show that for the ion spectrum, the signal to-background ratio can be significantly improved by using a quintuple-frequency probe beam. For the red peak of the electron spectrum, whether a quintuple-frequency probe beam or a quadruple-frequency probe beam is used, it is strongly disturbed by the intense background of the drive beam. For the blue peak of the electron spectrum, the drive beam background can be avoided by using a quintuple-frequency probe beam, while the bremsstrahlung background will be significantly enhanced. In general, quintuple-frequency Thomson scattering has significant advantages in the measurement of low atomic number plasmas, but not for high atomic number plasmas.