Review of heavy-ion inertial fusion physics

In this review paper on heavy ion inertial fusion(HIF),the state-of-the-art scientific results are presented and discussed on the HIF physics,including physics of the heavy ion beam(HIB)transport in a fusion reactor,the HIBs-ion illumination on a direct-drive fuel target,the fuel target physics,the uniformity of the HIF target implosion,the smoothing mechanisms of the target implosion non-uniformity and the robust target implosion.The HIB has remarkable preferable features to release the fusion energy in inertial fusion:in particle accelerators HIBs are generated with a high driver efficiency of~30%-40%,and the HIB ions deposit their energy inside of materials.Therefore,a requirement for the fusion target energy gain is relatively low,that would be~50-70 to operate a HIF fusion reactor with the standard energy output of 1 GWof electricity.The HIF reactor operation frequency would be~10-15 Hz or so.Several-MJ HIBs illuminate a fusion fuel target,and the fuel target is imploded to about a thousand times of the solid density.Then the DT fuel is ignited and burned.The HIB ion deposition range is defined by the HIB ions stopping length,which would be~1 mm or so depending on the material.Therefore,a relatively large density-scale length appears in the fuel target material.One of the critical issues in inertial fusion would be a spherically uniform target compression,which would be degraded by a non-uniform implosion.The implosion non-uniformity would be introduced by the Rayleigh-Taylor(R-T)instability,and the large densitygradient-scale length helps to reduce the R-T growth rate.On the other hand,the large scale length of the HIB ions stopping range suggests that the temperature at the energy deposition layer in a HIF target does not reach a very-high temperature:normally about 300 eV or so is realized in the energy absorption region,and that a direct-drive target would be appropriate in HIF.In addition,the HIB accelerators are operated repetitively and stably.The precise control of the HIB axis manipulation is also realized in the HIF accelerator,and the HIB wobbling motion may give another tool to smooth the HIB illumination non-uniformity.The key issues in HIF physics are also discussed and presented in the paper.

Non-Uniformity of Heavy-Ion Beam Irradiation on a Direct-Driven Pellet in Inertial Confinement Fusion

Heavy-ion-driven fusion （HIF） is a scheme to achieve inertial confinement fusion （ICF）. Investigation of the non-uniformity of heavy-ion beam （HIB） irradiation is one of the key issues for ICF driven by powerful heavy-ion beams. Ions in HIB impinge on the pellet surface and deposit their energy in a relatively deep and wide area. Therefore, the non-uniformity of HIB irradiation should be evaluated in the volume of the deposition area in the absorber layer. By using the OK1 code with some corrections, the non-uniformity of heavy-ion beam irradiation for the different ion beams on two kinds of targets were evaluated in 12-beam, 20-beam, 60-beam and 120-beam irradiation schemes. The root-mean-square （RMS） non-uniformity value becomes aRMS = 8.39% in an aluminum mono-layer pellet structure and aRMS = 6.53% in a lead-aluminum layer target for the 12-uranium-beam system. The RMS non-uniformity for the lead-aluminum layer target was lower than that for the mono-layer target. The RMS and peak-to-valley （PTV） non-uniformities are reduced with the increase in beam number, and low at the Bragg peak layer.

Laser ion source for heavy ion inertial fusion

The proposed heavy ion inertial fusion(HIF)scenarios require ampere class low charge state ion beams of heavy species.The laser ion source(LIS)is recognized as one of the promising candidates of ion beam providers,since it can deliver high brightness heavy ion beams to accelerators.The design of LIS for the HIF depends on the accelerator structure and accelerator complex following the source.In this article,we discuss the specifications and design of an appropriate LIS assuming two major types of the accelerators:radio frequency(RF)high quality factor cavity type and non-resonant induction core type.We believe that a properly designed LIS would satisfy the requirements of both types,while some issues need to be verified experimentally.

Diagnostic technique for measuring fusion reaction rate for inertial confinement fusion experiments at Shen Guang-III prototype laser facility

A study is conducted using a two-dimensional simulation program （Lared-s） with the goal of developing a technique to evaluate the effect of Rayleigh-Taylor growth in a neutron fusion reaction region. Two peaks of fusion reaction rate are simulated by using a two-dimensional simulation program （Lared-s） and confirmed by the experimental results. A neutron temporal diagnostic （NTD） system is developed with a high temporal resolution of - 30 ps at the Shen Guang-Ⅲ （SG-Ⅲ） prototype laser facility in China, to measure the fusion reaction rate history. With the shape of neutron reaction rate curve and the spherical harmonic function in this paper, the degree of Rayleigh-Taylor growth and the main source of the neutron yield in our experiment can be estimated qualitatively. This technique, including the diagnostic system and the simulation program, may provide important information for obtaining a higher neutron yield in implosion experiments of inertial confinement fusion.

Special epoxy silicone adhesive for inertial confinement fusion experiment

The effects of toughener and coupling agent on special epoxy silicone adhesive were discussed by researching the surface morphology characters, thermal properties and shear strength of the adhesive. The results indicate that silicone coupling agent (KH-550) can improve the shear strength of the epoxy silicone adhesive effectively. The mass fraction of the toughener in the epoxy silicone adhesive plays an important role in its properties. When the mass fraction of the toughener is less than 14%, the shear strength of the adhesive is low. When the mass fraction of the toughener is over 33%, thermal properties and shear strength of the adhesive decrease with the increasing of the toughener. The mass fraction of toughener of 25% results in good integral properties of the epoxy silicone adhesive. The morphologic analysis indicates that the micro-phase separation exists in the epoxy molecular chain and the silicone molecular chain of the epoxy silicone adhesive.

Optimization of laser illumination configuration for directly driven inertial confinement fusion

Optimum laser configurations are presented to achieve high illumination uniformity with directly driven inertial confinement fusion targets.Assuming axisymmetric absorption pattern of individual laser beams,theoretical models are reviewed in terms of the number of laser beams,system imperfection,and laser beam patterns.Utilizing a self-organizing system of charged particles on a sphere,a simple numerical model is provided to give an optimal configuration for an arbitrary number of laser beams.As a result,such new configurations as“M48”and“M60”are found to show substantially higher illumination uniformity than any other existing direct drive systems.A new polar direct-drive scheme is proposed with the laser axes keeping off the target center,which can be applied to laser configurations designed for indirectly driven inertial fusion.

Study of the asymmetry of hot-spot self-emission imaging of inertial confinement fusion implosion driven by high-power laser facilities

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 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 the 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 3μm,for characterization of higher-mode signatures such as Ps-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 the Shenguang 100 kJ class laser facility are also reported.

Progress in particle-beam-driven inertial fusion research: Activities in Japan

Research activities in Japan relevant to particle beam inertial fusion are briefly reviewed.These activities can be ascended to the 1980s.During the past three decades,significant progress in particle beam fusion,pulsed power systems,accelerator schemes for intense beams,target physics,and high-energy-density physics research has been made by a number of research groups at universities and accelerator facilities in Japan.High-flux ions have been extracted from laser ablation plasmas.Controllability of the ion velocity distribution in the plasma by an axial magnetic and/or electric field has realized a stable high-flux low-emittance beam injector.Beam dynamics have been studied both theoretically and experimentally.The efforts have been concentrated on the beam behavior during the final compression stage of intense beam accelerators.A novel accelerator scheme based on a repetitive induction modulator has been proposed as a cost-effective particle-beam driver scheme.Beam-plasma interaction and pulse-powered plasma experiments have been investigated as relevant studies of particle beam inertial fusion.An irradiation method to mitigate the instability in imploding target has been proposed using oscillating heavy-ion beams.The new irradiation method has reopened the exploration of direct drive scheme of particle beam fusion.

An improved deconvolution method for X-ray coded imaging in inertial confinement fusion

In inertial confinement fusion （ICF）, X-ray coded imaging is considered as the most potential means to diagnose the compressed core. The traditional Richardson-Lucy （RL） method has a strong ability to deblur the image where the noise follows the Poisson distribution. However, it always suffers from over-fitting and noise amplification, especially when the signal-to-noise ratio of image is relatively low. In this paper, we propose an improved deconvolution method for X-ray coded imaging. We model the image data as a set of independent Gaussian distributions and derive the iterative solution with a maximum-likelihood scheme. The experimental results on X-ray coded imaging data demonstrate that this method is superior to the RL method in terms of anti-overfitting and noise suppression.

Unequal-interval data fusion algorithm for inertial/gravity matching integrated navigation system

Inertial/gravity matching integrated navigation system can effectively improve the longendurance navigation ability of underwater vehicles.Through the analysis of the matching process,the problem of unequal-interval in matching trajectory is addressed by an unequal-interval data fusion algorithm which is based on the unequal-interval characteristics analysis of the matching trajectory.Compared with previously available methods,the proposed algorithm improves the location precision.In conclusion,simulations of the integrated navigation system demonstrated the effectiveness and superiority of the proposed algorithm.

Effects of Atomic Mixing in Inertial Confinement Fusion by Multifluid Interpenetration Mix Model

The effects of atomic-level rnixing are systemically investigated in a multifluid interpenetration mix model ,and results are compared with the single-fluid model＇s simulations and experimental data. It is shown that increasing the model free parameter α, shock Mach number, and the initial density discontinuity makes the mix length and fraction of mixing particle increase, resulting in the lower shock temperatures compared with the results of single-fluid model without mixing. Recent high-compressibility direct-drive spherical implosions on OMEGA are simulated by the interpenetration mix modal. The calculations with atomic mixing between fuel and shell match quite well with the observations. Without considering any mixing, the calculated neutron yields and ion temperatures are overpredicted; while inclusion of the interpenetration mix model with the adjustable parameter α could fit the simulated neutron yields and ion temperatures well with experimental data.

Relativistic Heavy Ion Collider and the Large Hadron Collider for Heavy Ion Fusion

Heavy Ion Fusion makes use of the Relativistic Heavy Ion Collider at Brookhaven National Lab and the Large Hadron Collider in Geneva, Switzerland for Inertial Confinement Fusion. Two Storage Rings, which may or may not initially be needed, added to each of the Colliders increases the intensity of the Heavy Ion Beams making it comparable to the Total Energy delivered to the DT target by the National Ignition Facility at the Lawrence Livermore Lab. The basic Physics involved gives Heavy Ion Fusion an advantage over Laser Fusion because heavy ions have greater penetration power than photons. The Relativistic Heavy Ion Collider can be used as a Prototype Heavy Ion Fusion Reactor for the Large Hadron Collider.

Distributed H_∞ fusion filter design for INS/WSN integrated positioning system

In order to keep stable navigation accuracy when the blind node （BN） moves between two adjacent clusters, a distributed fusion method for the integration of the inertial navigation system （INS） and the wireless sensor network （WSN） based on H∞ filtering is proposed. Since the process and measurement noise in the integration system are bounded and their statistical characteristics are unknown, the H∞ filter is used to fuse the information measured from local estimators in the proposed method. Meanwhile, the filter can yield the optimal state estimate according to certain information fusion criteria. Simulation results show that compared with the federal Kalman solution, the proposed method can reduce the mean error of position by about 45% and the mean error of velocity by about 85 %.

INFORMATION FUSION TECHNOLOGY FOR FSINS/DR/BEIDOU DOUBLE-STAR IN LAND FIGHTING-VEHICLE

The fiber strapdown inertial navigation system （FSINS）/dead reckoning （DR）/Beidou double-star integrated navigation scheme is proposed aiming at the need of land fighting-vehicle independence positioning. The measurement information fusion technology is studied by introducing the FSINS/DR/Beidou double-star integrated scheme. Several specific methods for the information fusion are discussed, and a Kalman filter is designed for the information fusion. Experimental results show that the design of the integrated scheme can improve the positioning accuracy of the navigation system.

Optimization of hole-boring radiation pressure acceleration of ion beams for fusion ignition

In contrast to ion beams produced by conventional accelerators,ion beams accelerated by ultrashort intense laser pulses have advantages of ultrashort bunch duration and ultrahigh density,which are achieved in compact size.However,it is still challenging to simultaneously enhance their quality and yield for practical applications such as fast ion ignition of inertial confinement fusion.Compared with other mechanisms of laser-driven ion acceleration,the hole-boring radiation pressure acceleration has a special advantage in generating high-fluence ion beams suitable for the creation of high energy density state of matters.In this paper,we present a review on some theoretical and numerical studies of the hole-boring radiation pressure acceleration.First we discuss the typical field structure associated with this mechanism,its intrinsic feature of oscillations,and the underling physics.Then we will review some recently proposed schemes to enhance the beam quality and the efficiency in the hole-boring radiation pressure acceleration,such as matching laser intensity profile with target density profile,and using two-ion-species targets.Based on this,we propose an integrated scheme for efficient high-quality hole-boring radiation pressure acceleration,in which the longitudinal density profile of a composite target as well as the laser transverse intensity profile are tailored according to the matching condition.

DGPS/INS Data Fusion for Land Navigation

The interest for land navigation has increased for the recent years. With the advent of the Global Position System (GPS) we have now the ability to determine the absolute position anywhere on the globe. The problem is that the GPS systems work well only in open environments with no overhead obstructions and they are subject to large unavoidable errors when the reception from some of the satellites are blocked. This occurs frequently in urban environments, forests and tunnels. GPS systems require at least four “visible” satellites to maintain a good position fix. In many situations in which higher level of accuracy is required, the navigation cannot be achieved by GPS alone. This paper discusses the design of a reliable multisensor fusion algorithm using GPS and Inertial Navigation System in order to decrease the implementation cost of such systems on land vehicles. The major contribution of this paper is in the definition of the possible developments and research axes in land navigation.

A Novel Voronoi Based Particle Filter for Multi-Sensor Data Fusion

Seamless and reliable navigation for civilian/military application is possible by fusing prominent Global Positioning System (GPS) with Inertial Navigation System (INS). This integrated GPS/INS unit exhibits a continuous navigation solution with increased accuracy and reduced uncertainty or ambiguity. In this paper, we propose a novel approach of dynamically creating a Voronoi based Particle Filter (VPF) for integrating INS and GPS data. This filter is based on redistribution of the proposal distribution such that the redistributed particles lie in high likelihood region;thereby increasing the filter accuracy. The usual limitations like degeneracy, sample impoverishment that are seen in conventional particle filter are overcome using our VPF with minimum feasible particles. The small particle size in our methodology reduces the computational load of the filter and makes real-time implementation feasible. Our field test results clearly indicate that the proposed VPF algorithm effectively compensated and reduced positional inaccuracies when GPS data is available. We also present the preliminary results for cases with short GPS outages that occur for low-cost inertial sensors.

Sensor fusion for heading angle estimation based on random forest algorithm

To improve the accuracy of the calculation of a heading angle under magnetic interference,magnetometers and inertial measurement units(IMUs)were fused.The observation value of the heading angle was deduced on the basis of the modeling of the magnetometer error and the analysis of the relation of the magnetometer triaxial output and the distribution characteristics of the magnetic field at two adjacent time periods.Meanwhile,the gyro state and angular velocity increment were used as the basis of the IMU to calculate the prediction value of the heading angle.With the changes in the heading angle and environmental interference,a random forest(RF)algorithm was used to iteratively calculate the weights to fuse the observation value of the heading angle based on the magnetometer and the prediction value of the heading angle based on the IMU.The results show that relative to the common sensor fusion method,the proposed sensor fusion method based on the RF algorithm achieved an approximate 60%improvement in heading angle accuracy.Hence,the proposed method can effectively improve the accuracy of the heading angle under magnetic interference by using an RF algorithm to calculate the output weights of the magnetometer and IMU.

A fitting formula for electron–ion energy partition fraction of 3.54-MeV fusion alpha particles in hot dense deuterium–tritium plasmas

Based on our previous work(Phys.Plasmas 25 012704(2018)),a fitting formula is given for electron-ion energy partition fraction of 3.54-MeV fusion alpha particles in deuterium-tritium(DT) plasmas as a function of plasma mass density ρ,electron temperature T_(e),and ion temperature T_(i).The formula can be used in a huge range of the plasma state,where ρ varies between 1.0 g/cc~10.0^(3) g/cc and both T_(e) and T_(i) change from 0.1 keV to 100.0 keV.Relativistic effect for electrons is investigated including the effect of the projectile recoil in the plasmas at T_(e)≥ 50.0 keV.The partition fraction for T_(e)>T_(i) is found to be close to that for T_(e)=T_(i). The comparisons with other fitting results are made at some plasma densities when T_(e)=T_(i),and the difference is explained.The fitting result is very close to the calculated one in most cases,which is convenient for the simulation of alpha heating in hot dense DT plasmas for inertial confined fusion.

基于IMU-LiDAR紧耦合的煤矿防冲钻孔机器人定位导航方法

防冲钻孔机器人是冲击地压矿井卸压的关键设备,其在复杂卸压巷道的精确地图构建和的稳定导航是实现钻孔作业智能化的基础和前提。在分析激光雷达点云畸变成因和同步定位与地图构建(SLAM)算法缺陷的基础上,设计了基于惯性测量单元(IMU)连续时间轨迹的点云畸变矫正方法,建立了激光雷达和IMU的数据融合模型,提出了基于IMU-LiDAR紧耦合的防冲钻孔机器人定位建图方法。根据煤矿卸压巷道特点建立了密闭坡道模型,开展了建图效果仿真分析,结果表明,所提算法在定位精度、轨迹误差方面均优于现有常用算法。在此基础上,设计了基于改进人工势场法和快速扩展随机树的动态路径规划方法,建立了适用于防冲钻孔机器人的路径规划与导航融合方案,并设计了2种仿真运动场景,结果表明,所提路径规划方法在全局路径规划和动态路径规划的平均路径长度、平均运行时间、平均生成节点数等方面均具有较好的综合性能。为了进一步验证防冲钻孔机器人定位导航方法的实用性,在校内模拟巷道、地面实验基地和井下卸压巷道等场景下开展了多组对比实验,结果表明:将IMU数据与LiDAR数据紧耦合后,所提方法的定位建图精度明显提高,在特征退化场景中具有优越的定位建图性能,且规划路径的运算效率和路径代价方面均具有良好的表现,验证了所提定位导航方法在多种场景中的可行性和优越性。