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In inertial confinement fusion, quantitative and high-spatial resolution ($$< 10\,\upmu $$ < 10 μ m) measurements of the X-rays self-emitted by the hotspot are critical for studying the physical processes of the implosion stagnation stage. Herein, the 8 ± 0.39-keV monochromatic X-ray distribution from the entire hotspot is quantitatively observed in 5-$$\upmu $$ μ m spatial resolution using a Kirkpatrick–Baez microscope, with impacts from the responses of the diagnosis system removed, for the first time, in implosion experiments at the 100 kJ laser facility in China. Two-dimensional calculations along with 2.5% P2 drive asymmetry and 0.3 ablator self-emission are congruent with the experimental results, especially for the photon number distribution, hotspot profile, and neutron yield. Theoretical calculations enabled a better understanding of the experimental results. Furthermore, the origins of the 17.81% contour profile of the deuterium-deuterium hotspot and the accurate Gaussian source approximation of the core emission area in the implosion capsule are clarified in detail. This work is significant for quantitatively exploring the physical conditions of the hotspot and updating the theoretical model of capsule implosion.

To study the effects of chunk mixing, the implosion experiments using capsules filled with deuterated foam (CDF capsule) were carried out on the Shenguang laser facility. Three types of the CDF capsules, namely the capsules without Au dopant, with micrometer Au dopant, and with atomic Au dopant, were used in the experiments. The neutron yields, the size, and the emission intensity of the hotspots were measured. The CDF capsules without Au dopant produced the highest neutron yield and the largest hotspot size at the time of peak emission. The capsules with micrometer or atomic Au dopant showed similar reduced neutron yield and hotspot size. The time-resolved hotspot emissions showed different behaviors between different capsules. One-dimensional simulations were carried out to understand the implosion dynamics of the CDF capsule without Au dopant, and to provide the thermodynamic conditions that the Au dopant would experience during the implosion. The effects of Au dopant were then discussed qualitatively.

A high-neutron yield platform imploded by a thin shell target is generally built to probe nuclear science problems, and it has the advantages of high neutron yield, ultrashort fusion time, micro fusion zone, isotropic and monoenergetic neutron. Some analytical models have been proposed to interpret exploding-pusher target implosion driven by a long wavelength laser, whereas they are imperfect for a 0.35 μm laser implosion experiment. When using the 0.35 μm laser, the shell is ablated and accelerated to high implosion velocity governed by Newton’s law, ablation acceleration and quasi-adiabatic compression models are suitable to explain the implosion of a laser direct-drive thin shell target. The new analytical model scales bang time, ion temperature and neutron yield for large variations in laser power, target radius, shell thickness, and fuel pressure. The predicted results of the analytical model are in agreement with experimental data on the Shenguang-III prototype laser facility, 100 kJ laser facility, Omega, and NIF, it demonstrates that the analytical model benefits the understanding of experiment performance and optimizing the target design of high neutron yield implosion.

An experiment has been conducted at the Shenguang-Ⅲ prototype laser facility, demonstrating the application of x-ray fluorescence imaging (XRFI) in diagnosing laser-driven hydrodynamic instability systems in planar geometry. An aluminum (Al)-foam target was used, including a modulated Al disk followed by a low density poly-4-methyl-1-pentene foam cylinder which was doped with titanium (Ti) dioxide nanoparticles to serve as the tracer layer. A blast wave was driven through the rippled interface, triggering the development of hydrodynamic instabilities and the growth of the perturbation. Vanadium plasma radiation dominated by He-α x-rays, was generated with a delay in time, inducing the emission of Ti K-shell fluorescent photons from the tracer layer. A Ross Pair Imager with matched scandium and Ti filters was employed to provide two-dimensional quasi-monochromatic fluorescent images, and the temporal evolution of the perturbation structures in the tracer layer was successfully observed. Furthermore, one-dimensional fluorescent intensity profiles across the perturbation structures were extracted and compared with the simulation results via a combination of the MULTI code, a buoyancy-drag model, a self-similar analysis and an imaging code. The boundaries of the measured profiles were shown to be connected together due to the small initial length of the tracer layer and the large boundary width caused by the curved interfaces and blurring effects, which made the absolute positions of the perturbation structures inaccessible. This research suggests that XRFI works well in qualitatively diagnosing the instability evolution and the experimental design has to be modified to further improve its performance in achieving quantitative information.

Implosion asymmetry is a crucial problem quenching ignition in the field of inertial confinement fusion. A forward-calculation method based on 1D and 2D hydrodynamic simulations has been developed to generate and to study the x-ray images of hot-spot self-emission, indicating asymmetry integrated over the entire drive pulse. It is shown that the x-ray imaging photon energy should be higher to avoid the influence of remaining shell. The contour level (percentage of the maximum emission intensity) and spatial resolution should be as low as possible, optimally less than 20% and 3 microns, for characterization of higher-mode signatures such as P8 to P12 by x-ray self-emission images. On the contrary, signatures of lower-mode such as P2 remain clear at all contour levels and spatial resolutions. These key results can help determine the optimal diagnostics, laser and target parameters for implosion experiments. Recent typical hot-spot asymmetry measurements and applications on Shenguang 100kJ-class laser facility are also reported.

The two-laser entrance hole (LEHs) spherical hohlraum energetic experiments with all 48 laser beams and two laser pulse shapes at the 100 kJ level laser facility were investigated. In this work, the time-resolved radiation temperature measured by multi-angle x-ray diodes agreed well with LARED simulations, and the peak radiation temperature was up to 260 eV with the laser power of 45 TW. Meanwhile, the backscattered laser energy fraction was less than 5% in the majority of shots, which proposed a low level of laser–plasma interaction (LPI) effect in the spherical hohlraum. However, in the shaped pulse shots with capsules, the stimulated Raman scattering (SRS) of smaller incident angle lasers was significantly increased to 15%. The measured SRS spectrum and LARED simulations showed that the increase in the LPI effects caused by the ablated CH plasma was around 0.1Nc (Nc is the critical density). In summary, according to the experimental results, the x-ray conversion efficiency of the vacuum spherical hohlraum was 85%–88% in 3 ns square pulses and 89%–93% in 3.6 ns shaped pulses. It was closer to that of the two-LEH cylindrical hohlraum at the Shen-Guang and NIF facilities.

The technique of x-ray fluorescence imaging (XRFI) has been applied to the high-energy-density (HED) jet experiments on the SG-III prototype laser facility. The jet was produced by the interaction of the laser driven shock with the perturbed Ti disk. The fluorescence emission of the Ti ejecta was pumped by the V He-α emission and recorded using a Ross Pair Imager with an optimized configuration. We achieved a spatial resolution of 35 μm and a temporal resolution of 1 ns. We also developed a method to infer the density distribution of the jet from the fluorescence images and discussed the conditions under which this method was accurate. These experiments provided insight into the characteristics of a HED jet and implied that XRFI is a promising way for studying HED hydrodynamics.

The first implosion tuning experiment with a shaped pulse driven was performed on the SGIII laser facility by using 2D X-ray radiography. Under the careful design, we obtained the driven symmetry both in the picket and peak. The experimental results show that the P2/P0 asymmetry can be tuned by varying the fraction energy in the inner cone both in the picket and peak. The radiation symmetry at the peak is consistent with our simulation. However, the radiation symmetry in first 0.5 ns (picket) had an unexpected negative P2/P0, which is different from the simulation; it may be caused by inner cone absorption in the tent which supported the capsule.

Two neutron time-of-flight (nToF) detectors have been employed to measure the neutron time-of-flight spectrum in different lines-of-sight, i.e., at the equator plane and the south pole, on Shenguang-III (SG-III) laser facility. The contribution of scattered neutrons has been calculated with the Monte Carlo code JMCT for each nToF detector. The results show that the scattered neutron spectrum is dominated by neutrons scattered on materials in the experiment hall, including the vacuum chamber. The shape of the scattered neutron spectrum depends on the view line, which has been observed with nToF detectors located in the experiment hall of the SG-III laser facility. A method based on the convolution of the calculated neutron time-of-flight spectrum and the instrument response function has been developed for the ion temperature determination. The calculated neutron spectra with the contribution of scattered neutrons can fit the measured results. No obvious ion temperature anisotropy has been observed on the SG-III laser facility at present.Two neutron time-of-flight (nToF) detectors have been employed to measure the neutron time-of-flight spectrum in different lines-of-sight, i.e., at the equator plane and the south pole, on Shenguang-III (SG-III) laser facility. The contribution of scattered neutrons has been calculated with the Monte Carlo code JMCT for each nToF detector. The results show that the scattered neutron spectrum is dominated by neutrons scattered on materials in the experiment hall, including the vacuum chamber. The shape of the scattered neutron spectrum depends on the view line, which has been observed with nToF detectors located in the experiment hall of the SG-III laser facility. A method based on the convolution of the calculated neutron time-of-flight spectrum and the instrument response function has been developed for the ion temperature determination. The calculated neutron spectra with the contribution of scattered neutrons can fit the measured results. No obvious ion temperature anisotropy has been observed on the S...

We present the first integrated implosion experiments which were carried out on the SG-III Laser facility in 2015. Vacuum hohlraums and squared laser pulses were used in the experiments. The purpose of the experiments was to demonstrate the one-dimensional implosion performance at low-convergence ratios. To characterize the implosion performance, the hohlraum energetics, the implosion dynamics and the nuclear products were measured. In particular, the radiation flux was diagnosed through laser entrance hole at different angles by an array of flat response detectors, and the energy and the spectrum of the back-scattered lasers were monitored for 8 laser beams which correspond to 2 beams in each cone at the lower hemisphere. Moreover, the hotspot shape was imaged using KB microscopes of high spatial resolution simultaneously from the equator and polar views. Taking advantage of the high resolution, some detailed structures in the hotspots were noticed. For the best implosion performances, the neutron yields over 1D calculation reached 50% at the convergence-ratios of 15.

The cylindrical vacuum hohlraum energy at the SGIII laser facility [X. T. He and W. Y. Zhang, Eur. Phys. J. D 44, 227 (2007) and W. Zheng et al., High Power Laser Sci. Eng. 4, e21 (2016)] is investigated for the first time. The hohlraum size and the laser energy are intermediate between the Nova and NIF typical hohlraum experiments. It is found that the SGIII hohlraum exhibits an x-ray conversion efficiency of about 85%, which is more close to that of the NIF hohlraum. The LARED simulations of the SGIII hohlraum underestimate about 15% of the radiation flux measured from the laser entrance hole, while the capsule radiation drive inferred from the x-ray bangtime is roughly consistent with the experiments. The underestimation of the SGIII hohlraum radiation flux is mainly caused by the more enclosed laser entrance hole in the LARED simulation. The comparison between the SGIII and NIF hohlraum simulations by LARED indicates that the LARED generally underestimates the measured radiation flux by 15% for the hi...

Directly driven cryogenic target implosion experiments are performed on the SGIII prototype laser facility. X-ray pinhole images reveal frozen condensation on the sealing film. The influence of the condensation on the delivery of laser energy to the capsule surface is then quantified experimentally. It is found that, with a carefully chosen pre-pulse duration, the influence can be reduced, and the neutron yield is increased by an order of magnitude. Subsequently, the cryogenic layered capsule and cryogenic gas-filled capsule are imploded using 6.5-kJ laser energy. The implosion performance is characterized by the neutron yield, the 2D self-emission images of the in-flight shell, and the primary proton spectrum. The neutron yield is 2 × 107 for the gas-filled capsule and 2.8 × 107 for the layered capsule. The 2D self-emission images of the in-flight shell exhibit significant implosion asymmetry. The energy downshift of the proton spectrum is used to infer the areal density. For the gas-filled capsule, the spectrum is downshifted by 0.1 MeV, yielding an areal density of 1–3 mg/cm2. For the layered capsule, the spectrum is downshifted by 0.5 MeV, yielding an areal density of 4–6 mg/cm2. Improving the implosion symmetry would help to further increase the areal density.

The implosion dynamics is the most important metrics for assessing the progress toward ignition of an inertially confined fusion experiment. A high spatial resolution monochromatic x-ray imaging system based on the spherically bent crystal is developed to measure the implosion trajectory. The density distribution of the imploding capsules can be inferred with more accurately from monochromatic trajectories. The self emission of the imploded core will be restrained by spectral resolution and the setup of the imaging system. Also the variations of the backlighters' intensity will not be seen in the images. It has been demonstrated on SGII laser facility at the first time. The ablator remaining mass and the implosion velocity, which are the important ablator parameters, are calculated from the monochromatic trajectories. And the results are contrasted to the 1D hydrodynamics simulations.