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.

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.

Spherically bent crystal imaging is a measurement technique that can be used to achieve quasi monochromatic high-resolution imaging in experimental studies of inertial confinement fusion based on high power laser facilities. With a high-resolution backlight arrangement design similar to that of point projection, the spherically bent crystal imaging system developed is applied to 10 kJ-level Shenguang facilities for hydrodynamic instability, implosion compression trajectory, and other experimental studies of laser-induced plasmas. When it is applied to interface trajectory measurement during the ablation and compression of spherical samples, the spherically bent crystal imaging has the advantages of a large field of view, quasi-monochromaticity, and self-smoothing of backlight intensity distribution. The influences of the resolution in the meridian direction and that in the sagittal direction on one-dimensional interface trajectory measurement are balanced by optimizing imaging parameter design without changing the arrangement parameters of the imaging system. Even with a larger backlight, the spatial resolution of the interface trajectory absorption image is improved, and the signal-to-noise ratio of the image is also effectively enhanced. An accuracy of 2.1% is achieved in implosion velocity measurement by combining the optimized spherically bent crystal imaging system with the alternative target design.

The time-resolved X-ray spectroscopy measurement system based on X-ray streak camera technology is indispensable diagnostic equipment in the study of laser inertial fusion research and high-energy-density physics. However, limited by the effective photocathode length of the X-ray streak tube, the time-resolved spectral measurement system usually used has the shortcomings of narrow spectrum range and poor spectral resolution.In order to overcome the shortcomings, a novel dual-channel streak tube is developed, which consists of a photocathode, a prefocusing electrode group in temporal direction, an electric quadrupole lens electrode group, a main focusing electrode group in temporal direction, a deflector plate, and a phosphor screen. The photocathode has two slits. When X-rays are incident, two electron beams can be emitted simultaneously. The electric quadrupole lens electrode group is composed of 8 arc electrodes. Two electric quadrupole lenses are formed by the 8 arc electrodes in the spatial direction. Two electron beams emitted from the cathode of the streak tube are first accelerated and prefocused by the prefocusing electrode group in the time direction, and then compressed by the main focusing electrode group in the time direction. In the spatial direction, two electron beams are focused by the two electric quadrupole lenses independently. This novel streak tube structure can focus two electron beams at the same time, thereby increasing the effective photocathode length and maintaining the compact structure of streak tube without increasing the aberration.The cathode voltage of the designed streak tube is –12 kV, the distance from cathode to grid is 5 mm, and the cathode-grid field strength is 2.4 kV/mm. The cathode is divided into two sections, the spacing between sections is about 13 mm, the length of each section is more than 20 mm, the magnification of the image converter tube is about 1.56 times, the distance between the cathode and the phosphor screen is 300 mm, and the longest size along the cathode direction is 90 mm. The test results of the performance of the streak tube show that the actual effective cathode length of the developed tube reaches 44 mm, the spatial resolution is better than 15 lp/mm, and the deflection sensitivity is better than 40 mm/kV. The effective cathode and spatial resolution of the tube can be increased to 50 mm and 25 lp/mm by further optimizing the structure of the tube and removing the image intensifier with a high sensitivity image recording system, respectively.

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.

In inertial confinement approaches to fusion, the asymmetry of target implosion is a major obstacle to achieving high gain in the laboratory. A recently proposed octahedral spherical hohlraum makes it possible to naturally create spherical target irradiation without supplementary symmetry control. Before any decision is made to pursue an ignition-scale laser system based on the octahedral hohlraum, one needs to test the concept with the existing facilities. Here, we report a proof-of-concept experiment for the novel octahedral hohlraum geometry on the cylindrically configured SGIII laser facility without a symmetry control. All polar and equatorial self-emission images of the compressed target show a near round shape of convergence ratio 15 under both square and shaped laser pulses. The observed implosion performances agree well with the ideal spherical implosion simulation. It also shows limitations with using the existing facilities and adds further weight to the need to move to a spherical port geometry for future ignition laser facilities.

A 100 kJ-level laser facility has been designed to study inertial confinement fusion physics in China. This facility incorporates various diagnostic techniques, including optical, x-ray imaging, x-ray spectrum, and fusion product diagnostics, as well as general diagnostics assistance systems and central control and data acquisition systems. This paper describes recent developments in diagnostics at the facility.

The streak cameras have very important applications in Inertial Confinement Fusion (ICF), including x-ray streak cameras and optical streak cameras. At present, they are still the core diagnostic devices with the highest temporal resolution in this field. This paper introduces the performance and characteristics of two main types of the streak cameras widely used in the field of laser fusion both domestic and international. They are equipped with coaxial electrode double-focus electron optics streak tube and bilamellar electron optics streak tube respectively. In terms of specifications of streak camera, the criteria of dynamic range of streak camera are emphasized, the dynamic range data of today's international high performance streak cameras are presented. The paper also introduces several important research progresses in the development of streak camera technologies, including advanced backlighting ultraviolet fiducial system, neutron radiation tolerant device and gated cathode technology.

间接驱动惯性约束聚变研究中,获得高内爆速度是实现点火,提升聚变增益的关键.通过对内爆烧蚀压缩过程的测量,能够获得内爆速度和剩余质量等内爆动力学重要的物理量,实现烧蚀层材料、厚度以及激光波形等参数的优化.近几年在神光系列装置上,演示了常规的应用狭缝成像的内爆烧蚀压缩过程测量技术,发展了基于球面弯晶成像的高分辨单能内爆烧蚀压缩过程测量技术.通过对球面弯晶成像系统设计的持续改进以及内爆烧蚀压缩过程测量技术的优化,结合实验室和系统原位标定结果,建立了高分辨的内爆压缩流线诊断技术,采用替代靶方式,实现内了爆速度不确定度2.1％的测量精度.

The injecting time of the picosecond laser in an indirect-drive integrated fast ignition experiment was measured by using an x-ray streak camera. Despite overlapping spatially and temporally in experiments, the soft x-ray signal from the nanosecond laser ablating the inner wall of an Au hohlraum and the hard x-ray signal from the bremsstrahlung radiation of hot electrons generated by a picosecond laser were separated by different image processes by filtering and collimating the two signals differently. The time sequence between the two x-ray signals was analyzed to extract the injection time of the picosecond laser relative to the hohlraum emission. By tracking the neutron yield as a function of the injection time of the picosecond laser, a clear positive correlation between the neutron yield enhancement and the derived injection times was exhibited. The heating effect of the picosecond laser was confirmed. It is concluded that this method could be used to measure the injecting time and validate the picosecond laser injection.

The ShenGuang-III (SG-III) laser facility was developed by the laser fusion research center (LFRC) for inertial confinement fusion (ICF) studies in China. Over 80 diagnostics have been installed at the SG-III laser facility, including optical diagnostics, x-ray imaging diagnostics, x-ray spectrum diagnostics, fusion product diagnostics and general diagnostics assistant systems, as well as central control and data acquisition systems. Various ICF experiments have also been performed at the SG-III laser facility. The first experiment explored the laser-target coupling process, including investigations of hohlraum radiation flux and laser energy coupling efficiency. The second experiment explored ablation and implosion physics, including shell asymmetry and implosion trajectory. The third experiment explored stagnation, hotspot dynamics and the nuclear phase of the implosion.

In the field of indirect-drive inertial confinement fusion, temporal and spatial diagnosis of X-ray is very important to the imploded process researches and the simulate procedure verification. According to the temporal, spatial and spectral characteristics of X-ray radiation, many X-ray imaging diagnosis devices were successfully developed. Along with the development of ICF research, especially the Shenguang III facility establishment, our X-ray imaging diagnosis capability has been increasingly powerful. Some of the novel diagnosis equipment even have more excellent characteristics than that kind of diagnosis equipment abroad.

In recent years, hohlraum experiments have been performed extensively on Shenguang series laser facilities in the context of laser indirect-drive inertial confinement fusion. Multiple aspects about the hohlraumenergetics, drive symmetry and plasma condition are studied by a variety of methods resolving different photon ranges and multiple viewing areas. To improve the experimental uncertainty, several diagnostics are optimized and calibrated, also the power balance and pointing accuracy of laser beams are evaluated and improved. These works lead a rapid progress on hohlraum experimental capabilities and a series of successful experimental campaigns. In order to further optimize the hohlraum performance, other hohlraum geometry (the spherical hohlram with six LEHs and the cylindrical hohlraum with six LEHs) and hohlraum wall material (depleted Uranium and foam Au) are explored as well. Hohlraum experiments and modeling on Shenguang series laser facilities demonstrated quantitative understanding of the laser conversion, X-ray ablation and plasma motion in different regions.

On Shenguang Ⅲ laser facility,32 laser beams were symmetrically injected a gas-filled hohlraum to create plas-ma situation which is close to the ignition condition.An X-ray framing camera on the polar station and an X-ray streak camera near the pole were utilized to obtain the temporal and spacial evolution X-ray images of the plasma from the hohlraum wall and near the laser entrance hole(LEH),which were used to analyse the LEH closure feature of the hohlraum with various LEH size. The experimental results clearly demonstrated the evolution of laser spot motion,plasma expanding near the LEH and closure of the LEH,which supplied the foundation to optimize the LEH dimension.

The first observation of the K-shell photoabsorption edge of strongly coupled aluminum generated by intense x-ray radiation-driven shocks is reported. By using a "dog bone" gold hohlraum as an x-ray converter, colliding shocks compression and preheating shielding are achieved to generate an unexplored state with a density of 5.5 g/cm(3) and temperature of 0.43 eV (the ion-ion coupling parameter Gii is around 240). The time-resolved K-shell photoabsorption edges are measured with a crystal spectrometer using a short x-ray backlighter. The broadenings and redshifts of the edges are studied by using the slope fitting of the edge and quantum molecular dynamics calculations. This work shows that the K-edge of aluminum driven by laser-converted radiation provides a novel capability to probe WDM at extended conditions. Copyright (C) EPLA, 2017

In order to mitigate the effect of the strong electromagnetic pulse,which produces laser-plasma interactions,we designed a new streaked X-ray spectrometer (SXS)enclosed within a well-sealed,electromag-netic interference-free cavity.The SXS can cover a wide selection of spectral windows using interchangeable Bragg crystals and by appropriate adjustment of the Bragg angle.The SXS has been used to observe time-re-solved X-ray spectrum in the 2.5 keV to 3.5 keV photon-energy range,resulting in a demonstrated spectral res-olution of about 13 at 2960 eV with a time resolution of 10 ps.The observed time and spectral resolutions dem-onstrate the applicability of the SXS for studies of laser-produced plasmas.

Caesium iodide (CsI) thin films have attracted much attention due to good electron transport and emission properties in the soft X-ray and extreme ultraviolet range. With the rapid development of nuclear physics, high energy physics and astrophysics, the requirements for CsI film photocathodes become increasingly severe, and it is therefore of considerable interest to develop CsI photocathodes with high quantum efficiency (QE) and stable performance. However, the internal mechanisms of QE variation and photocathode aging are not entirely clear or certain up to date. In this paper, the recent progress on CsI film photocathodes is reviewed and some controversial issues are introduced. Several perspectives are also proposed in the end.

We present a novel photocathode which can make x-ray streak cameras to be of a flat spectral response in the x-ray energy range of 0.1-5 keV. The photocathode consists of two layers of gold foils with optimized thickness ratio and structures. The photocathode was calibrated, and it is shown that a flat spectral response has been achieved.

为了获得大面积自支撑的高效率X射线光电转换材料,通过化学气相沉积和热蒸发镀膜工艺,制备出了大面积自支撑的CsI/PC膜,其中PC(聚碳酸酯)膜厚度为300 nm,CsI膜厚度在100 nm到1μm.通过扫描电镜、X射线衍射仪研究了镀膜速度和受潮对样品表面形貌结构的影响.利用MANSON光源的X射线对不同沉积速率和受潮程度的样品的X射线转换效率进行了研究.在北京同步辐射装置标定了样品X射线光电转换效率,其响应灵敏度峰值大于3000 μA/W;将样品作为X射线光电阴极应用在X射线条纹相机上,在神光Ⅲ主机平台上获得了清晰的X射线图像.