直接驱动快点火Au-CD锥壳靶的研制

介绍了近年在直接驱动快点火锥壳靶研制方面取得的进展。采用带止口金锥的设计提高金锥与微球的装配精度,讨论了芯轴电镀工艺中尖端效应的影响。采用飞秒激光加工实现聚合物微球打孔,讨论了激光扫描方式对打孔质量的影响。     

Laser induced fast ignition made realistic by relativistic velocities-dream or reality?

Due to the recent developments in high power lasers it is suggested to accelerate a micro-foil by the laser pressure to relativistic velocities. The time dependent velocity of this micro-foil is calculated analytically for pulsed constant laser intensity. The accelerated foil collides with a target creating a shock wave on impact. The shock wave parameters are calculated within the context of relativistic fluid dynamics.It is suggested to use the energy of the relativistic micro-foil to ignite a pre-compressed target with a density relevant for fusion ignition. The equations are written and solved for the collision between the micro-foil and the very dense target. The criteria for shock wave ignition and heat wave ignition are used to show that one needs significantly less laser energy for heat wave ignition.The present scheme shows that nuclear fast ignition by micro-foil impact could be attained in the near future with lasers that are currently under construction.     

Application of High Energy Protons in Inertial Confinement Fusion by Using the Fast Ignitor Concept for DT Fusion

A short-laser-pulse driven ion flux is examined as a fast ignitor candidate for inertial confinement fusion. The main mechanism for ion acceleration is charge separation in a plasma due to high-energy electrons driven by the laser inside the target. Another very new branch of fast ignition research is the investigation of the use of laser generated proton beams. In the present paper aims to provide insights into the feasibility of the fast ignition concept with high energy beams of protons generated in laser–plasma interactions. The optimum parameters of an ion beam and laser pulse that are suitable for an ignition spark in a hot precompressed DT fuel are estimated as a rough guide. Also, in this paper we estimate the radius of Deuterium–Tritium (DT) fuel pellet that is equal to the protons range in DT plasma.     

快点火物理及其对数值模拟的要求

快点火(fast ignition)是一种新的惯性约束聚交点火方式。实验和理论研究表明其点火环节是非常复杂和困难的问题。研究快点火需要深入地进行数值模拟。报告主要从分析物理出发,探讨快点火对数值模拟的要求,同时结合实际情况进行讨论。快点火主要包括三个过程,即内爆预压缩、超强激光在次临界等离子体中和在超临界密度等离子体中的传播(成道和打洞)、超热电子的产生及其在介质,特别是稠密介质中的传输和高温点火区的形成。研究认为:研究预压缩不仅需要一维、二维,而且需要三维激光靶耦合总体程序;超热电子需要包括电磁场的Fokker-Planck方程描述;点火过程的等离子体流体力学则需要考虑电子、离子双流运动方程,而且应包括电磁场。PIC程序可用来研究局部的细节,并提供上述方程所需要的参数。此外,报告还简述了近两年来的快点火实验和一些国家的未来的计划。     

The Potential of Fast Ignition and Related Experiments with a Petawatt Laser Facility

A model of energy gain induced by fast ignition of thermonuclear burn in compressed deuterium-tritium fuel, is used to show the potential for 300× gain with a driver energy of 1 MJ, if the National Ignition Facility (NIF) were to be adapted for fast ignition. The physics of fast ignition has been studied using a petawatt laser facility at the Lawrence Livermore National Laboratory. Laser plasma interaction in a preformed plasma on a solid target leads to relativistic self-focusing evidenced by x-ray images. Absorption of the laser radiation transfers energy to an intense source of relativistic electrons. Good conversion efficiency into a wide angular distribution is reported. Heating by the electrons in solid density CD₂ produces 0.5 to 1 keV temperature, inferred from the D-D thermo-nuclear neutron yield.     

Alternative schemes for the inertial fusion energy

The advanced target designs are requiring a lower laser energy for ignition and promising higher energy gains. Two approaches are under development within the European inertial fusion energy project HiPER: the fast ignition scheme with energetic electrons and the shock ignition scheme. The fundamental physical issues and major experimental works related to the alternative ignition schemes as well as the reactor designs are discussed.     

Recent results on Nova

On the Nova Laser at LLNL, we have recently demonstrated many of the key elements required for assuring that the next proposed laser, the National Ignition Facility (NIF) will reach ignition. In particular, we have achieved a drive of 300 eV in laser heated hohlraums; have shown good understanding and control of symmetry in hohlruams; created large NIF-Scale plasmas with plasma and irradiation conditions relevant to NIF targets that showed low levels of plasma instabilities; demonstrated a good understanding of hydrodynamic instability and subsequent pusher/fuel mix in implosions by means of spectroscopic tracers; and performed integrated implosion experiments that have performed well even under stringent convergences of order 25, which is well into the NIF ignition target regime.     

Study of the asymmetry of hot-spot selfemission 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 1 D and 2 D 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 3 mm, for characterization of higher-mode signatures such as P_8–P_(12) by x-ray self-emission images. On the contrary, signatures of lower-mode such as P_2 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.     

多孔注入冷冻靶快速降温过程瞬态特性研究

高度均匀光滑的燃料冰层是惯性约束聚变冷冻靶成功点火的物质前提,其制备关键是在靶丸外建立均匀的球形温度场并进行精确控制。本文针对多孔注入冷冻靶系统,建立了三维仿真模型,数值研究了冷冻靶温度场稳态分布与瞬态降温特性,并分析了接触热阻、氦气压力等因素的影响。结果表明：冷臂温度恒定时,靶丸与充气管接触位置为低温区,激光入射口正对处为高温区,最大温差为003 mK;硅臂加热块功率突降后,靶丸表面最大温差在025 s内急剧上升至8788 mK,温度场均匀性显著恶化;与硅爪 套筒完美接触相比,低温胶层的存在可有效改善降温过程中温度场的恶化,但降温响应时间明显增加;1～10 kPa氦气压力范围内,快速降温过程中靶丸温度响应迅速,且最大温差峰值较小,有利于维持靶丸表面的温度均匀性。     

Nova target physics program and the Nova upgrade laser

Summary Recent advances in ICF target design and performance have made possible the achievement of ignition and gain with 1–2 MJ laser drive energy, as against the 5–10 MJ necessary to achieve high gain in the earlier designs. Ignition and propagating burn can be achieved at the lower energy by increasing the hohlraum temperature and, thereby increasing the pressure driving the imploding fusion capsule. Nova experiments continue to address the target physics of radiatively driven targets, such as laser-plasma interaction physics, the efficiency of laser light conversion to X-rays, hohlraum characterization and design, hydrodynamic stability, and implosion physics. Recent experiments on Nova have also demonstrated 1.3 times higher hohlraum temperature than previously predicted. This latter demonstration is the key achievement leading to the Nova Upgrade proposal. These combined results, together with those from experiments to study the interaction of high-power laser light with target plasmas, indicate that the capsule drive and symmetry conditions required for ignition and net gain can be achieved with a properly designed upgrade of the existing Nova facility.Success in the Nova Upgrade objective would firmly establish target and driver requirements for achieving high yield and high gain and would support a decision to construct a Laboratory Microfusion Facility (LMF) for defense applications and an Engineering Test Facility (ETF) for energy applications by the end of the first decade of the next century. Nova Upgrade experiments would focus on the target physics necessary to determine the minimum driver energy required to achieve ignition and high-gain laser fusion. The thermonuclear yield produced (up to 20 MJ) would be used to study the effects of fusion microexplosions on potential LMF and ETF reactor chamber materials. This information would permit development of the most efficient and least costly designs for the LMF and the ETF.In collaboration with W. H. Lowdermilk, N. Frank, C. D. Henning, John R. Murray, M. T. Tobin, J. R. Smith, E. K. Storm, J. D. Lindl, J. D. Kilkenny, J. T. Hunt, and J.B. Trenholme.     

快点火靶金锥制备工艺

锥壳靶是惯性约束聚变快点火实验研究中的一种重要靶型。本工作采用精密车床加工与电镀技术制备锥壳靶用不同角度的金锥。主要介绍金锥电镀金层的制备工艺,讨论了电镀液配方、pH值、镀前处理、尖端效应等对金锥金层质量的影响。     

Investigation of Fuel Energy Gain for Tritium-Poor Fuels in Fast Ignition Fusion Approach

One of the most fascinating ignition schemes for the inertial fusion energy that might be feasible is fast ignition.Its targets are ignited on the outside surface so there is no need to low density and high temperature center is required by central hot spot ignition.Fast ignition concept is noteworthy for a simple but fundamental reason:In principle it requires less total energy input to achieve ignition.In this paper,fuel energy and fuel energy gain of nearly pure deuterium capsule are calculated.This capsule is ignited by a deuterium-tritium seed,which would reduce the tritium inventory to a few percentages.The variations of fuel energy gain versus fuel density have been studied and submitted.On the basis of different physical parameters the following results of the investigation are presented and discussed.The energy gain curves for different tritium concentrations are found and limiting gain curves are derived.Finally,tritium-poor fast ignitor is compared to equimolar deuterium-tritium fast ignitor.     

Plasma ignition threshold disparity between silver nanoparticle-based target and bulk silver target at different laser wavelengths

Plasma ignition threshold of nanoparticle-based and bulk silver targets was measured in air. The plasma was initiated by a Nd:YAG laser at wavelengths of 355, 532, and 1064 nm. The plasma ignition was monitored utilizing the prominent Ag I line at 546.5 nm. Lower ignition thresholds of the nanoparticle-based silver target were estimated at 0.4?±?0.02, 0.34?±?0.04, and 0.27?±?0.035 J cm~(-2) coupled with the different laser wavelengths, respectively. In contrast, the bulk silver target plasma exhibited an order of magnitude higher ignition threshold. A three orders of magnitude enhanced emission intensity from the nano-based target over the bulk target was achieved at lower levels of laser irradiation. A reduction of the thermal diffusion length of the nanosilver was assumed in order to theoretically predict this reduction in the plasma threshold. In addition, the effect of self-reversal on the resonance lines was taken into consideration.     

Visualizing an ignition process of hydrogen jets containing sodium mist by high-speed imaging

In severe accident scenarios for sodium-cooled fast reactors, it is desirable to gradually consume hydrogen generated by various ex-vessel phenomena without posting a challenge to containment integrity. An effective means is combustion of hydrogen jets containing sodium vapor and mist, but previous studies have been limited to determining ignition thresholds experimentally. The aim of this study was to visualize the ignition process in detail to investigate the ignition mechanism of hydrogen–sodium mixed jets. The ignition experiments of the hydrogen jet containing sodium mist were carried out under a condition of little turbulence. The ignition process was measured with an optical measurement system comprised of a high-speed camera and an image intensifier, and a spatial distribution of luminance was analyzed by image processing. Detail observation revealed that sodium mist particles burned as scattering sparks inside the jet and that hydrogen ignited around the mist particles. Additionally, the experimental results and a simple heat balance calculation indicated that the combustion heat of sodium mist particles could ignite the hydrogen as the heterogeneous ignition source in the fuel temperature range where the mist particle formation was promoted.     

快点火用氘代聚合物空心微球研究进展

氘代聚合物空心微球是惯性约束聚变快点火物理研究中亟需的一类靶丸。本文总结近年来国内外快点火物理实验中使用的氘代聚合物空心微球种类,介绍快点火物理实验对氘代聚合物空心微球质量的严苛要求和各类氘代聚合物空心微球的制备方法,重点阐述氘代聚合物空心微球质量的影响因素和研制进展,并指出氘代聚合物空心微球研制的发展方向。     

Energy and flux measurements of laser-induced silver plasma ions by using Faraday cup

Silver(Ag)plasma has been generated by employing Nd∶YAG laser(532 nm,6 ns)laser irradiation.The energy and flux of ions have been evaluated by using Faraday cup(FC)using time of flight(TOF)measurements.The dual peak signals of fast and slow Ag plasma ions have been identified.Both energy and flux of fast and slow ions tend to increase with increasing irradiance from 7 GW cm-2 to 17.9 GW cm-2 at all distances of FC from the target surface.Similarly a decreasing trend of energies and flux of ions has been observed with increasing distance of FC from the target.The maximum value of flux of the fast component is 21.2×1010cm-2,whereas for slow ions the maximum energy and flux values are 8.8 keV,8.2×1012 cm-2 respectively.For the analysis of plume expansion dynamics,the angular distribution of ion flux measurement has also been performed.The overall analysis of both spatial and angular distributions of Ag ions revealed that the maximum flux of Ag plasma ions has been observed at an optimal angle of～15°.In order to confirm the ion acceleration by ambipolar field,the self-generated electric field(SGEF)measurements have also been performed by electric probe;these SGEF measurements tend to increase by increasing laser irradiance.The maximum value of 232 V m-1 has been obtained at a maximum laser irradiance of 17.9 GW cm-2.     

The NIKE KrF laser fusion facility

NIKE is a second generation high power KrF laser now under construction at the Naval Research Laboratory. The project is a collaborative effort between NRL and Los Alamos National Laboratory. NIKE is designed to deliver more than 2 kJ of energy to target in a 600-m focal spot and a 4-ns pulse duration. Echelon free induced spatial incoherence (ISI) will be used to produce uniform target illumination. Flat targets will be ablatively accelerated to study both Rayleigh-Taylor and parametric instabilities. These results will have direct implications to direct-drive inertial confinement fusion for commercial energy applications. Reliable operation of a high power KrF laser is also an important goal of the NIKE laser, with the objective of 1000 target shots per year. This would be an important step in the development of the KrF laser as an ICF driver. NIKE is cheduled to begin target experiments in early 1994. If successful, these experiments will provide a technical basis to proceed with construction of an ignition facility.     

Advances in CTIX Accelerator Study

Several new experiments have been conducted on the UC Davis repetitive-pulsed spheromak-like compact toroid (SCT) accelerator (CTIX). (1) SCT density and kinetic energy density has been increased by gas puffing in the acceleration section. With gas puffing, SCT electrical to kinetic energy conversion efficiency has been increased to >20%. (2) SCT interaction with targets has been recorded with a fast visible imaging system, combined with target-region helium gas puffing for increased brightness. Images of both coherent waves and turbulent flow patterns were observed in the target region after the interaction. (3) A laser deflection density diagnostic has been improved to obtain better reliability and resolution. Operated with high-density gas-puffed SCTs, the second-generation diagnostic has successfully measured axial as well as radial deflection. The measured line averaged densities are in good agreement with a conventional quadrature laser interferometer.     

Fabrication and absolute calibration of B-dot probe for magnetic field measurement on a high power laser facility

The fabrication and absolute calibration of a B-dot probe is employed to measure the pulsed magnetic field at the Shenguang-II high power laser facility. Copper enameled silk with a cross section diameter of 0.1 mm is used to wind the one-turn coil with a 1 mm diameter. Two coils are paired and reversely linked to their respective circuits to form a differential B-dot probe that is sealed in and protected by a quartz shell. This B-dot probe is experimentally calibrated and then used to measure the pulsed magnetic field in laser targeting experiments at the Shenguang-II high power laser facility. Signals show a high performance of this B-dot probe. The common mode noise can be effectively canceled out by the differential pair. The magnetic field of over 300 T can be extrapolated at the location close to the target.