Velocity analysis of supersonic jet flow in double-cone ignition scheme

In the double-cone ignition schemes(DCIS), the deuterium–tritium target shell is ablated and compressed by a highpower nanosecond laser in Au-cones to generate plasmas. Under the actions of spherically symmetric compression and acceleration along the Au cone, they will be ejected out of the cone mouth and collide with each other. The plasmas experience conversion from kinetic energy to internal energy at the vertex of the geometric center of two Au cones that are symmetric to each other, because of which high-density fusion plasmas are preheated. This key physical process has undergone experimental verification on the Shenguang-II upgraded facility in China. Apparently, the improvement and optimization of the velocity of plasmas in hypersonic jet flow at the cone mouth are crucial for the success of the DCIS. In the DCIR7 experiment of the Shenguang-II upgraded facility, a velocity yield of approximately 130–260 km/s was achieved for the plasmas at the cone mouth, with a result of nearly 300 km/s based on numerical simulation. In this paper, theoretical analysis is performed as regards the process, in which target shells are ablated and compressed by laser to generate highvelocity plasmas ejected through jet flow. Based on this analysis, the formula for the velocity of plasmas in supersonic jet flow at the cone mouth is proposed. This study also provides measures that are more effective for improving the kinetic energy of plasmas and optimizing energy conversion efficiency, which can serve as theoretical references for the adjustment and optimization of processes in subsequent experiments.

Development of a monochromatic crystal backlight imager for the recent double-cone ignition experiments

We developed a monochromatic crystal backlight imaging system for the double-cone ignition(DCI) scheme, employing a spherically bent quartz crystal. This system was used to measure the spatial distribution and temporal evolution of the head-on colliding plasma from the two compressing cones in the DCI experiments. The influence of laser parameters on the x-ray backlighter intensity and spatial resolution of the imaging system was investigated. The imaging system had a spatial resolution of 10 μm when employing a CCD detector. Experiments demonstrated that the system can obtain time-resolved radiographic images with high quality, enabling the precise measurement of the shape, size, and density distribution of the plasma.

Ultrafast two-dimensional x-ray imager with temporal fiducial pulses for laser-produced plasmas

It is challenging to make an ultrafast diagnosis of the temporal evolution of small and short-lived plasma in two dimensions. To overcome this difficulty, we have developed a well-timed diagnostic utilizing an x-ray streak camera equipped with a row of multi-pinhole arrays. By processing multiple sets of one-dimensional streaked image data acquired from various pinholes, we are capable of reconstructing high-resolution two-dimensional images with a temporal resolution of 38 ps and a spatial resolution of 18 μm. The temporal fiducial pulses accessed from external sources can advance the precise timing and accurately determine the arrival time of the laser. Moreover, it can correct the nonlinear sweeping speed of the streak camera. The effectiveness of this diagnostic has been successfully verified at the Shenguang-II laser facility,providing an indispensable tool for observing complex physical phenomena, such as the implosion process of laser-fusion experiments.

液态铅铋电磁流量计初步标定实验与分析

铅铋合金(Lead-Bismuth Eutectic,LBE)是加速器驱动次临界系统主选冷却剂材料之一,其热工流量测量面临高温、强腐蚀等苛刻环境。电磁流量计(Electromagnetic flow-meter,EMFM)是目前国际上用于铅铋流量测量的主选设备之一。研究发现,铅铋电磁流量计的标定技术对于其准确测量具有重要作用。本文基于PREKY铅铋技术预研实验平台,对自主研制的高温铅铋电磁流量计进行了标定实验与分析。在温度为350oC、流量为3.8–4.5m3?h-1的工况下,获得了液态铅铋电磁流量计的标定公式。标定公式计算值与实验值之间的误差范围是-4.9%–5.9%。

Analytical model for Rayleigh-Taylor instability in conical target conduction region

This work builds an isobaric steady-state fluid analytical-physical model of the plasma conduction region in a conical target. The hydrodynamic instability in the double-cone ignition scheme^([21]) for inertial confinement fusion(ICF) proposed by Zhang is studied with the built model. With this idealized model, the relevant parameters, such as density, temperature,and length of the plasma in the conduction region of the conical target under long-pulse conditions are given. The solution of the proposed analytical model dovetails with the trend of the numerical simulation. The model and results in this paper are beneficial for discussing how to attenuate Rayleigh-Taylor instability in ICF processes with conical and spherical targets.

Fast electrons collimating and focusing by an ultraintense laser interacting with a high density layers

The use of a novel double-cone funnel target with high density layers （HDL） to collimate and focus electrons is investigated by two-dimensional particle-in-cell simulations. The proposed scheme can guide, collimate and focus electron beams to smaller sizes. The collimation reasons are analyzed by the quasi-static magnetic fields generation inside the beam collimator with HDL. It is found that the energy conversion efficiency is increased by a factor of 2.2 in this new scheme in comparison with the that without HDL. Such a target structure has potential for design flexibility and prevents inefficiencies in important applications such as fast ignition, etc.

Research of the Thermal Parameters and the Accuracy of Flow Measurement of the Biological Fuel

The heat parameters, the thermoanemometric flow-meter （TAF） errors and the experimental characteristics have been defined. The results of experiments were conducted with the help of physically-informational models allowing to realize all major thermal methods and their inherent informative options. The metrological evaluation was made and the sensitivity to the consumption of gas and liquid have been defined, their static and dynamic errors, followed by the comparison of costs according to these criteria. The developed method provides accurate measurement of volumetric flow of motor fuel 1.0-1.5% at heater temperature measurement accuracy of 1%.

Design, performance and application of a line-imaging velocity interferometer system for any reflector coupled with a streaked optical pyrometer system at the Shenguang-Ⅱ upgrade laser facility

The velocity interferometer system for any reflector(VISAR) coupled with a streaked optical pyrometer(SOP) system is used as a diagnostic tool in inertial confinement fusion(ICF) experiments involving equations of state and shock timing.To validate the process of adiabatically compressing the fuel shell through precise tuning of shocks in experimental campaigns for the double-cone ignition(DCI) scheme of ICF, a compact line-imaging VISAR with an SOP system is designed and implemented at the Shenguang-II upgrade laser facility. The temporal and spatial resolutions of the system are better than 30 ps and 7 μm, respectively. An illumination lens is used to adjust the lighting spot size matching with the target size. A polarization beam splitter and λ/4 waveplate are used to increase the transmission efficiency of our system. The VISAR and SOP work at 660 and 450 nm, respectively, to differentiate the signals from the scattered lights of the drive lasers. The VISAR can measure the shock velocity. At the same time, the SOP system can give the shock timing and relative strength. This system has been used in different DCI campaigns, where the generation and propagation processes of multi-shock are carefully diagnosed.

Laser pulse shape designer for direct-drive inertial confinement fusion implosions

Pulse shaping is a powerful tool for mitigating implosion instabilities in direct-drive inertial confinement fusion(ICF).However,the high-dimensional and nonlinear nature of implosions makes the pulse optimization quite challenging.In this research,we develop a machine-learning pulse shape designer to achieve high compression density and stable implosion.The facility-specific laser imprint pattern is considered in the optimization,which makes the pulse design more relevant.The designer is applied to the novel double-cone ignition scheme,and simulation shows that the optimized pulse increases the areal density expectation by 16%in one dimension,and the clean-fuel thickness by a factor of four in two dimensions.This pulse shape designer could be a useful tool for direct-drive ICF instability control.

Prediction of flow patterns during silo discharges using a finite element approach and its preliminary experimental verification

Obtaining a reliable discharge of particulate solids from a storage silo is a prerequisite to securing oper- ational adequacy in solids handling processes. If a silo is poorly designed, an unreliable interrupted discharge often occurs. In this study, an in-house finite element （FE） program was modified to predict the particulate solids flow patterns during discharges from silos, and the effect of a double-cone insert on such flow patterns. In FE modeling, a Eulerian approach was adopted with an assumption of steady-state flow-a state that greatly facilitated investigations on the effects of double-cone inserts on the flow of particulate solids. Predictions were carried out on whether the discharge was in mass flow or funnel flow, associated with the inclination angle of the silo＇s hopper. Predicted results were in agreement with the Jenike Chart, and proved that an upper lateral pressure ratio value gave a better critical hopper half angle to achieve mass flow （EN 1991-4, 2006）. The shape and size of the stagnant zone were further discussed to address the flow channel boundary between the flowing and static solids if the discharge was in a funnel pattern. Results also showed the effects of a double-cone insert on the flow patterns which con- verted silos from funnel flow to mass flow up to a certain hopper inclination angle and would improve the flow pattern even for shallower angles. Experiments were carried out to verify some of the predicted results. Some qualitative comparisons were made between the predicted results and experimental mea- surements, which indicated that further efforts are needed in predicting the shape of the stagnant zone （flow channel boundary） during funnel flow discharges.

Machine-learning guided optimization of laser pulses for direct-drive implosions

The optimization of laser pulse shapes is of great importance and a major challenge for laser direct-drive implosions.In this paper,we propose an efficient intelligent method to perform laser pulse optimization via hydrodynamic simulations guided by the genetic algorithm and random forest algorithm.Compared to manual optimizations,the machine-learning guided method is able to efficiently improve the areal density by a factor of 63%and reduce the in-fiight-aspect ratio by a factor of 30%at the same time.A relationship between the maximum areal density and ion temperature is also achieved by the analysis of the big simulation dataset.This design method has been successfully demonstrated by the2021 summer double-cone ignition experiments conducted at the SG-II upgrade laser facility and has great prospects for the design of other inertial fusion experiments.