Progress of Laser Fusion Research with GEKKO XII Glass Laser and KONGHO Project for Breakeven

The progress of laser fusion research is remarkable in obtaining the high density (100 times solid density) and high temperature plasma and in the understanding of the implosion physics. Thermonuclear neutrons of 1013 per shot and pellet gain of 0.2% have been achieved. The data bases of the laser fusion have been accumulated for the fusion ignition experiment and the achievement of the breakeven condition is estimated to be possible with 100 kJ blue laser.     

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.     

Application study on plasma ignition in aeroengine strut-cavity-injector integrated afterburner

To increase the thrust-weight ratio in next-generation military aeroengines,a new integrated afterburner was designed in this study.The integrated structure of a combined strut-cavity-injector was applied to the afterburner.To improve ignition characteristics in the afterbumer,a new method using a plasma jet igniter was developed and optimized for application in the integrated afterburner.The effects of traditional spark igniters and plasma jet igniters on ignition processes and ignition characteristics of afterburners were studied and compared with the proposed design.The experimental results show that the strut-cavity-injector combination can achieve stable combustion,and plasma ignition can improve ignition characteristics.Compared with conventional spark ignition,plasma ignition reduced the ignition delay time by 67 ms.Additionally,the ignition delay time was reduced by increasing the inlet velocity and reducing the excess air coefficient.This investigation provides an effective and feasible method to apply plasma ignition in aeroengine afterburners and has potential engineering applications.     

Ultrahigh Acceleration of Plasma Blocks by Nonlinear Forces for Side-On Laser Ignition of Solid Density Fusion Fuel

A fundamental difference of very high intensity laser interaction with plasmas from solid targets appears with lasing at picosecond (ps) pulse durations in contrast to pulses of nanosec- onds (ns). This can be seen from the more than 10,000 times higher acceleration with ps pulse du- rations than with thermal pressure determined interaction. A ps pulse duration produces instantly acting high-efficiency nonlinear (ponderomotive) electrodynamic force dominated acceleration in contrast to heating with longer pulses. The ps pulses accelerate high-density plasma blocks. This can be used by a new scheme of side-on driven laser fusion with generating a flame ignition in uncompressed fusion fuel of solid density resulting in a reaction velocity of more than 2000 km/s for DT.     

Ignition Approach by Neutral Beam Injection Heating in Impurity Contaminated Tokamak Reactors

Available heating power by neutral beam injection in a tokamak reactor is evaluated semi-empirically. Using this estimated value, device and plasma parameters to ignite the plasma in impurity contaminated tokamak reactors are investigated. By lowering the plasma density and concurrently by enlarging the plasma minor radius or aspect ratio, the difficulty of NBI heating can be avoided, and the ignition is almost always possible both for trapped ion mode and Alcator scaling laws.     

Numerical simulation of atmospheric pulse-modulated radio-frequency glow discharge ignition characteristics assisted by a pulsed discharge

A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulse-modulated(PM) radio-frequency(RF) glow discharge in atmospheric helium assisted by a sub-microsecond voltage excited pulsed discharge. The temporal evolution of discharge current density and electron density during PM RF discharge burst was investigated to demonstrate the discharge ignition characteristics with or without the pulsed discharge. Under the assistance of pulsed discharge, the electron density in RF discharge burst reaches the magnitude of 1.87 × 10~(17) m~(-3) within 10 RF cycles, accompanied by the formation of sheath structure. It proposes that the pulsed discharge plays an important role in the ignition of PM RF discharge burst. Furthermore, the dynamics of PM RF glow discharge are demonstrated by the spatiotemporal evolution of the electron density with and without pulsed discharge. The spatial profiles of electron density, electron energy and electric field at specific time instants are given to explain the assistive role of the pulsed discharge on PM RF discharge ignition.     

Study on the ignition process of a segmented plasma torch

Direct current plasma torches have been applied to generate unique sources of thermal energy in many industrial applications.Nevertheless,the successful ignition of a plasma torch is the key process to generate the unique source (plasma jet).However,there has been little study on the underlying mechanism of this key process.A thorough understanding of the ignition process of a plasma torch will be helpful for optimizing the design of the plasma torch structure and selection of the ignition parameters to prolong the service life of the ignition module.Thus,in this paper,the ignition process of a segmented plasma torch (SPT) is theoretically and experimentally modeled and analyzed.Corresponding electrical models of different stages of the ignition process are set up and used to derive the electrical parameters,e.g.the variations of the arc voltage and arc current between the cathode and anode.In addition,the experiments with different ignition parameters on a home-made SPT have been conducted.At the same time,the variations of the arc voltage and arc current have been measured,and used to verify the ones derived in theory and to determine the optimal ignition parameters for a particular SPT.     

Study on the influence of the discharge voltage on the ignition process of Hall thrusters

A high-speed charge-coupled device camera was used to capture images of the plume and acceleration channel of a Hall effect thruster during ignition at different discharge voltages. To better understand the influence of changes in the discharge voltage on the plasma parameters during thruster ignition, a particle-in-cell numerical model was used to calculate the distribution characteristics of the ion density and electric potential at different ignition moments under different discharge voltages. The results show that when the discharge voltage is high, the ion densities in the plume and acceleration channel are significantly higher at the initial phase of thruster ignition; with the gradual strengthening of the ignition process, the propellant avalanche ionization during thruster ignition occurs earlier and the pulse current peak increases. The main reason for these phenomena is that the change in the discharge voltage results in different energy acquisitions of the emitted electrons entering the thruster channel.     

Exploratory studies of tokamaks as fusion test reactors

Studies have been performed to explore various plasma burn scenarios for a tokamak test reactor which could follow the next generation of large tokamak experiments. Tradeoffs between an ignited burning plasma and a sub-ignited driven plasma are examined in terms of device size and performance as a fusion engineering test facility. It is found that plasma performance levels, measured by ignition margin, amplification factorQ, and fusion power output, increase with device size, more optimistic transport scaling laws, lower magnetic field ripple, and higher. The performance of a generally low stress (B ₀=4 T) reference device, with major radiusR=4.5 m and minor radiusa=1.3 m in a D-shaped (=1.6) plasma has been evaluated over a wide range of operating parameters. In particular, a moderate fusion power output of 300 MW is obtained, the driven plasma havingQ 10, an edge ripple of 1%, and a density ranging between 1.0 and 1.5×10¹⁴ cm^–3. The same device operated at a higher general level of stress (B ₀=5.3 T) is predicted to achieve ignition, but is not required for the mission of an engineering test facility and would entail greater technical risk.     

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。     

Road Map for a Modular Magnetic Fusion Program

During the past several decades magnetic fusion has made outstanding progress in understanding the science of fusion plasmas, the achievement of actual fusion plasmas and the development of key fusion technologies. Magnetic fusion is now technically ready to take the next step: the study of high gain fusion plasmas, the optimization of fusion plasmas and the continued development and integration of fusion technology. However, each of these objectives requires significant resources since the tests are now being done at the energy production scale. This paper describes a modular approach that addresses these objectives in specialized facilities that reduces the technical risk and lowers cost for near term facilities needed to address critical issues.     

Present Status and Future Prospects of Laser Fusion Research at ILE Osaka University

Reviewed are the present status and future prospects of the laser fusion research at the ILE Osaka.The Gekko XII and Peta Watt laser system have been operated for investigating the implosion hydrodynamics,fast ignition, and the relativistic laser plasma interactions and so on.In particular,the fast ignition experiments with cone shell target have been in progress as the UK and US-Japan collaboration programs.In the experiments,the imploded high density plasmas are heated by irradiating 500 J level peta-watt laser pulse.The thermal neutron yield is found to increase by three orders of magnitude by injecting the peta-watt laser into the cone shell target.The Rayleigh-Taylor instability experiment results are also reviewed is this paper.     

The Feasibility of Applying AC Driven Low-Temperature Plasma for Multi-Cycle Detonation Initiation

Ignition is a key system in pulse detonation engines(PDE). As advanced ignition methods, nanosecond pulse discharge low-temperature plasma ignition is used in some combustion systems, and continuous alternating current(AC) driven low-temperature plasma using dielectric barrier discharge(DBD) is used for the combustion assistant. However, continuous AC driven plasmas cannot be used for ignition in pulse detonation engines. In this paper, experimental and numerical studies of pneumatic valve PDE using an AC driven low-temperature plasma igniter were described. The pneumatic valve was jointly designed with the low-temperature plasma igniter,and the numerical simulation of the cold-state flow field in the pneumatic valve showed that a complex flow in the discharge area, along with low speed, was beneficial for successful ignition. In the experiments ethylene was used as the fuel and air as oxidizing agent, ignition by an AC driven low-temperature plasma achieved multi-cycle intermittent detonation combustion on a PDE, the working frequency of the PDE reached 15 Hz and the peak pressure of the detonation wave was approximately 2.0 MPa. The experimental verifications of the feasibility in PDE ignition expanded the application field of AC driven low-temperature plasma.     

Effects of the critical breakdown path on the ignition performance in heaterless hollow cathodes

The critical breakdown path(CBP) has a significant impact on the breakdown voltage curve and the ignition time of heaterless hollow cathodes(HHCs). To determine the pattern of the variation in the CBP position and its impact on ignition performance, a numerical model named the CBP evaluation(CBPE) was established in this paper to calculate the CBP of a HHC. The CBPE model can be used to screen various potential breakdown paths to identify those that are most likely to satisfy the Townsend breakdown conditions, which are denoted as CBPs. To verify the calculation accuracy of the CBPE model, 4.5 A-level HHC ignition tests were conducted on HHCs with three different structures. By comparing the test results and the calculated results of the breakdown voltage, the calculation errors of the CBPE under three HHC conditions ranged from 1.6% to 5.8%, and the trends of the calculated results were consistent with those of the test results. The ignition test also showed the characteristics of the breakdown voltage curve and the ignition time for the three HHCs. Based on the CBPE model, an in-depth analysis was conducted on the mechanism of the patterns revealed by the tests. The main conclusions are presented as follows:(1) the CBP always shifts from the long path to the short path in the HHCs with an increasing gas flow rate; and(2) the ignition time of the HHCs depends on the position of the CBP because different CBP positions can cause different mechanisms of heat transfer from the plasma to the emitter. This study can guide the optimization of the CBP position and the corresponding ignition times of HHCs.     

Effect of shock wave formation on propellant ignition in capillary discharge

In order to study the effect of shock wave formation on propellant ignition in capillary discharge, the shock wave formation process was analyzed using experimental and theoretical methods; the plasma jet temperature was measured, and closed bomb and 30 mm gun experiments were carried out. The results show that the first shock wave has a smaller value and larger range of influence, while the second shock wave has a larger value and smaller range of influence. A plasma jet can generate a shock wave at the nozzle according to the calculated plasma pressure and velocity, which is well confirmed by experiments and calculations. The plasma jet temperature is high during the formation of a shock wave and then decreases sharply. Plasma ignition can increase the burning rate of a propellant by about 30% by increasing the burning surface area of the propellant. Compared to conventional ignition, the average maximum chamber pressure and average muzzle velocity of plasma ignition are increased by 9.1 MPa and 29.3 m·s−1(∼3%), respectively, in a 30 mm gun. Plasma ignition has strong ignition ability and short ignition delay time due to the generation of a shock wave. By increasing the burning rate of the propellant, the muzzle velocity can be greatly improved when the maximum chamber pressure increases a little. The characteristics of the shock wave can be applied in the application of the capillary discharge plasma. For example, it can be applied in fusion, launching and combustion.     

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。     

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。     

Energetics of Beam Driven D-Cycle Plasmas

The energetic characteristics of deuterium fueled fusion plasmas well below ignition and aided by neutral beam injection are investigated with the perspective of eventually being utilized in a fusion hybrid reactor. Particular emphasis is placed on the three modes of D-fusion cycles and on the role of the neutral beam ions as they effect the plasma energetics. Ion concentrations corresponding to steady state operation of the fusion cycles as well as total reaction rates and fusion gains are evaluated for regimes which tend to be identified with a two energy component reactor. The associated interrelation requirements on the temperature, density and magnetic confinement of the plasma are illustrated. It is shown how operational plasma constraints can be substantially relaxed by high energetic deuteron injection while retaining an energy viability sufficient for a synergetic fusion reactor concept.     

Report of the U.S. Department of Energy Fusion Energy Sciences Advisory Committee Panel on Burning Plasma Physics

This is the report of a panel set up by the U.S. Department of Energy Fusion Energy Sciences Advisory Committee (FESAC) in response to a charge letter on October 5, 2000, from Dr. Mildred Dresselhaus, then Director of the DOE's Office of Science. In that letter, Dr. Dresselhaus asked the FESAC to investigate the subject of burning plasma science. The report addresses several topics, including the scientific issues to be addressed by a burning plasma experiment and its major supporting elements, identification of issues that are generic to toroidal confinement, and the role of the Next-Step Options (NSO) Program.