Liang Guo

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.

Double-shell targets offer significant advantages in ignition margins and energy gain. We conducted theoretical studies and radiation hydrodynamic simulations to achieve efficient implosion of the double-shell targets driven by Z-pinch dynamic hohlraum (ZPDH). Theoretical models incorporating the ablator ablation, target implosion, and shell collisions are developed. The final implosion velocity can be theoretically predicted based on the given target and radiation drive parameters. The theoretical predictions exhibit a good agreement with the results from radiation hydrodynamic simulations, with deviations within 10%. Then, an optimal target structure using the random walk algorithm is designed. It is found that a target with a 3 mm radius can be ignited and yields energy of 165 MJ under a 285.6 eV radiation-driven source produced by ZPDH with a 50 MA load current. These findings provide valuable insights for designing double- or multi-shell targets in inertial confinement fusion.

The spatiotemporal evolution of electromagnetic fields generated by a relativistic-intensity laser pulse irradiating a capacitor–coil target was diagnosed using proton radiography. In the experiments, both an electromagnetic pulse (EMP) propagating at approximately the speed of light immediately after the laser–target interaction and a magnetic field generated by the coil current were observed. The results demonstrate a clear spatiotemporal separation between the proton signals induced by the EMP and those induced by the coil magnetic field. This separation enables accurate measurement of the magnetic field generated by the coil current after the EMP has subsided.

In previous studies, the pulsed strong magnetic fields generated by the laser-driven coils were usually overestimated. One of the reasons is that the self-generated magnetic field and the coil-induced magnetic field exhibit different power-law decay behaviors with respect to probe distance. We design an insulated coil target to measure the net coil-produced magnetic field, and to accurately infer the magnetic field inside a magnetized hohlraum. A magnetic field is generated by laser irradiation on a capacitor-coil target featuring an x-ray maze structure. The gold hohlraum inside the coil is slitted to eliminate the diamagnetic current and enable the external magnetic field to penetrate the gold hohlraum. To delay the closure of the slit, an x-ray maze is designed between the two capacitor plates. In this work, a pulsed magnetic field with a peak strength over 500 T is generated in the magnetized hohlraum using 1053 nm lasers with pulse length of 2 ns and energy of above 1.6 kJ. An energy conversion efficiency of ∼8% from laser energy to magnetic field energy was achieved. This work provides technical support for magnetized high-energy-density physics research.

X-ray backlighting is a crucial diagnostic technique in inertial confinement fusion (ICF) experiments, enabling the observation of the geometrical structure of an imploding capsule. However, x-ray emission from a short-pulse laser illuminating a metallic strip often proves insufficient and unstable, resulting in high noise levels in observed images that complicate data analysis. In this study, we propose a comprehensive framework for multi-level noise reduction in x-ray backlighting images, integrating data synthetic techniques with a novel multi-level noise removal method based on Frequency Residual U-Net (FR-UNet). The observed x-ray images are decomposed into distinct signal and noise components. The signal is simulated based on the underlying backlighting geometry, incorporating a range of relevant parameters to accurately model the setup variance. The noise model is constructed through a comprehensive analysis of both shot noise and periodic speckle noise. The FR-UNet model is trained on synthetically generated images and subsequently applied to experimental data. Our framework demonstrates a significant improvement in image quality, with the signal-to-noise ratio increasing from ∼10–20 dB to ∼30 dB. Further evaluation on an open dataset shows favorable results, achieving a peak signal-to-noise ratio of ∼35 and a structural similarity index measure of ∼0.96. This approach offers substantial potential for enhancing image quality and diagnostic accuracy in inertial confinement fusion (ICF) experiments and can be adapted to similar applications involving x-ray backlighting systems in other high-energy physics contexts.

In this paper, we present a novel method for image signal recovery from a scintillator-based X-ray imaging system inherently corrupted by impulsive noise. This approach combines a physically-based image synthesis process with deep neural networks to effectively reduce neutron-induced impulsive noise. For the synthesis, experimental data are meticulously decomposed into constituent components based on different physical processes: the clean signal from self-emitted X-rays, shot noise induced by photons, impulsive noise from neutrons, and electronic noise from digital devices, each analyzed and modeled independently. A Legendre function is employed to model the clean hot spot signal, emphasizing its asymmetry. The noise power spectrum, derived from experimental data, is utilized for shot noise simulation, while the statistical characteristics of impulsive noise are analyzed and integrated into the synthesis process. A deep neural network, leveraging the U-Net architecture, is trained on these synthetic images and subsequently applied to real experimental data. This method significantly enhances the signal-to-noise ratio of experimental data, improving from ~ -30 to -20 dB to ~ 20 to 30 dB, and maintains high fidelity in clean signal representation. Our approach demonstrates significant potential to improve image quality and diagnostic accuracy in experimental settings and could be adapted for similar applications in other research contexts involving imaging systems in radiation environments.

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.

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 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.

In indirect-drive hohlraum, the heated plasmas from the laser entrance hole (LEH) and bubbles blow radially inward with time, which plays an important role in the evolution of hohlraum plasmas. Previously, the boundary of the LEH and bubble plasmas is measured using time-integrated x-ray images or x-ray images at several discrete moments. A new experiment is conducted to study the continuous temporal behaviors of the LEH and bubble plasmas, which utilizes a gas-filled hohlraum truncated on one side. Compared experiments are performed with 3 different LEH diameters (1.0 mm, 1.2 mm, and 1.4 mm). An x-ray streak camera (XSC) is employed for the first time to diagnose the continuous temporal x-ray images of the LEH and bubble plasmas, which are also measured by an x-ray framing camera (XFC) at several discrete moments. The XSC and the XFC are combined for the first time and give coincident results for the movement of the LEH and bubble plasmas. In addition, 2 sets of flat-response x-ray diode (FXRD) measure the total x-ray flux from both the LEH and the open end and thus give the radiation temperature (Tr) in the hohlraum. The Tr from the LEH end shows a visual increase compared with that from the open end, due to the LEH closure, which is coincident with the temporal x-ray images. This work presents more precise and detailed description for the continuous movement of the LEH and bubble plasmas, which is beneficial to optimize our radiation hydrodynamic code and hohlraum design for ignition.