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.

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 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.

A longer pulse, lower adiabat drive in a low gas-fill hohlraum is an inertial confinement fusion design with potential higher gain, but has challenges such as the less tamped wall plasma. Thus, it is necessary to alter the laser spot regions to control low-mode drive asymmetry when using such laser pulses. The hollow wall is designed [Vandenboomgaerde et al 2018 Phys. Plasmas 25 012713] and has been demonstrated with experiments to be effective in holding back the gold bubble expansion [Depierreux et al 2020 Phys. Rev. Lett . 125 255 002]. This paper presents experimental and simulation results demonstrating that hollow wall hohlraums effectively reduce laser spot motion. Experiment results indicate that the laser spot position in hollow wall hohlraum moves less than that in classical solid hohlraum, similar data are obtained by 2D simulation. This reduction in motion is beneficial for improving P4 drive asymmetry.

We present measurements of the 2p-3d transition opacity of a hot molybdenum–scandium sample with nearly half-vacant molybdenum M-shell configurations. A plastic-tamped molybdenum–scandium foil sample is radiatively heated to high temperature in a compact D-shaped gold Hohlraum driven by ∼30 kJ laser energy at the SG-100 kJ laser facility. X rays transmitted through the molybdenum and scandium plasmas are diffracted by crystals and finally recorded by image plates. The electron temperatures in the sample in particular spatial and temporal zones are determined by the K-shell absorption of the scandium plasma. A combination of the IRAD3D view factor code and the MULTI hydrodynamic code is used to simulate the spatial distribution and temporal behavior of the sample temperature and density. The inferred temperature in the molybdenum plasma reaches a average of 138 ± 11 eV. A detailed configuration-accounting calculation of the n = 2–3 transition absorption of the molybdenum plasma is compared with experimental measurements and quite good agreement is found. The present measurements provide an opportunity to test opacity models for complicated M-shell configurations.

A self-consistent and precise method to determine the time-dependent radiative albedo, i.e., the ratio of the reemission flux to the incident flux, for an indirect-drive inertial confinement fusion Hohlraum wall material is proposed. A specially designed symmetrical triple-cavity gold Hohlraum is used to create approximately constant and near-equilibrium uniform radiation with a peak temperature of 160 eV. The incident flux at the secondary cavity waist is obtained from flux balance analysis and from the shock velocity of a standard sample. The results agree well owing to the symmetrical radiation in the secondary cavity. A self-consistent and precise time-dependent radiative albedo is deduced from the reliable reemission flux and the incident flux, and the result from the shock velocity is found to have a smaller uncertainty than that from the multi-angle flux balance analysis, and also to agree well with the result of a simulation using the HYADES opacity.

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.

Indirectly driven inertial confinement fusion implosions using a three-step-shaped pulse are performed at a 100 kJ laser facility. At late time of the pulse, deposition of laser energy and distribution of X-ray radiation are significantly disturbed by motion of gold plasma in the original gas-filled cylindrical hohlraum with gold wall. As a result, owing to the lack of X-ray drive at the equator of the capsule, an unacceptable oblate implosion is produced. In the I-raum modified from the above cylindrical hohlraum, the initial positions of outer laser spots and gold bubbles are appropriately shifted to modify the disturbed radiation distribution due to plasma evolution, resulting in a spherically symmetric drive on the capsule. In the implosion shots with almost the same drive pulse, owing to improved symmetry, an spherical hotspot is observed in the new I-raum, and YOS (the ratio of measured neutron yield over simulated one) is up to 30%, while an oblate hotspot is observed in the cylinder, and YOS is only 13%. The simulation calculations and experimental measurements show that the I-raum can be used to significantly reduce the impact of gold bubble expansion in the three-step-shaped pulse driven implosion, which helps to tune the drive and implosion symmetry, and to improve its over-all performance.

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.

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.

A recently proposed octahedral spherical hohlraum with six laser entrance holes (LEHs) is an attractive concept for an upgraded laser facility aiming at a predictable and reproducible fusion gain with a simple target design. However, with the laser energies available at present, LEH size can be a critical issue. Owing to the uncertainties in simulation results, the LEH size should be determined on the basis of experimental evidence. However, determination of LEH size of an ignition target at a small-scale laser facility poses difficulties. In this paper, we propose to use the prepulse of an ignition pulse to determine the LEH size for ignition-scale hohlraums via LEH closure behavior, and we present convincing evidence from multiple diagnostics at the SGIII facility with ignition-scale hohlraum, laser prepulse, and laser beam size. The LEH closure observed in our experiment is in agreement with data from the National Ignition Facility. The total LEH area of the octahedral hohlraum is found to be very close to that of a cylindrical hohlraum, thus successfully demonstrating the feasibility of the octahedral hohlraum in terms of laser energy, which is crucially important for sizing an ignition-scale octahedrally configured laser system. This work provides a novel way to determine the LEH size of an ignition target at a small-scale laser facility, and it can be applied to other hohlraum configurations for the indirect drive approach.

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.

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.

A new diagnostic platform for more accurate diagnosis of the peak radiation temperature on ablator has been proposed. A nearly constant radiation temperature was obtained by two laser entrance holes spherical hohlraum. The peak radiation temperature on ablator was determined by the shock wave technique. A high-quality burn-through image of a two-step-shaped Au ablator was obtained in the experiment. The simulated mass ablation rate agrees well with the experimental result, while the peak radiation temperature measured by flat-response x-ray detectors outside the hohlraum was of ∼20 eV’s lower than that obtained by the shock wave technique. This deviation results in ∼20%’s decrease in the mass ablation rate in the simulation. Thus, the new diagnostic platform can provide more accurate peak radiation temperature diagnosis. This can greatly support the inertial confinement fusion ignition target design.

以实验室中的 X 射线管作为光源，配合 CMOS 探测器涂层闪烁体纤维面板实时在线记录设备，建立了柱面弯晶检测平台。通过高精度的同轴转台设计，将整个柱面弯晶曲面转换为多个线段区间来分别进行检测，并对光路排布以及谱线的位置移动进行了解析计算。选用铁靶材 X 射线管 （K α 特征谱线波长为 0.193 6 nm） 作为实验光源，曲率半径 120 mm 的石英柱面弯晶作为样品，实验获得了清晰的铁特征谱线 （Fe-K α 和 Fe-K β ）。通过分析柱面弯晶上 9 个采样位置的图像，发现 Fe-K α 谱线位置移动了 96 μm，对应的半径偏差为 40 μm，?R/R为 0.033%。经过检测的石英柱面弯晶已经在大型激光装置上应用，并获得高质量的光谱图像，证明了该实验方法对柱面弯晶品质检测的有效性。

Plasma density and temperature can be diagnosed by x-ray line emission measurement with crystal, and bent crystals such as von Hamos and Hall structures are proposed to improve the diffraction brightness. In this study, a straightforward solution for the focusing schemes of flat and bent crystals is provided. Simulations ith XOP code are performed to validate the analytical model, and good agreements are achieved. The von Hamos or multi-cone crystal can lead to several hundred times intensity enhancements for a 200 upmu mplasma source. This model benefits the applications of the bent crystals.