包含超热电子输运的激光聚变总体方程组计算方法的研究及其应用

本文的两个主要内容:(1)论述超热电子输运方程的数值解法。超热电子多群扩解方程为退缩抛物型方程,其求解要点是能量空间变换及系数平均,总能空间特殊群处理,隐式差分及求自洽电场的线性分割法。(2)概述了考虑超热电子输运功能的激光聚变总体程序(JB-2)的功能,并列举了符合实验图象的激光平面靶计算实例。JB-2程序已成为高功率激光打靶研究和靶设计的重要工具。     

与ICF快点火相关的激光等离子体研究

高强度紫外飞秒激光作为ICF“快点火”的点火驱动器具有独特的优势。第一,紫外光具有更大的临界密度,产生超热电子区域更靠近燃料区,这就简化了所有与把能量输运到燃料区的物理过程;第二,按照超热电子温度Iλ2定标率,在“快点火”要求的强度下（1020w/cm2）,紫外光刚好能够产生可以与燃料区高效率耦合的超热电子温度（1MeV）;此外,紫外光具有更好的可聚焦性,在较低的能量下就可以达到要求的强度。目前,大多数关于紫外飞秒激光与固体靶相互作用的研究集中于吸收机制和软X射线方面,关于硬X射线和超热电子方面的研究非常缺乏。Teubner等利用K-α线谱方法研究了KrF激光在固体靶中的吸收和超热电子产生,Broughto和Fedosjevs等研究了脉冲宽度为1～100ps的KrF激光辐照固体靶产生     

电子磁谱仪法测量超热电子温度

利用超热电子磁谱仪测量了紫外超短脉冲激光与固体等离子体相互作用产生超热电子的能谱,在无预脉冲、激光强度为1017 W/cm2 条件下,紫外超短脉冲激光与固体(Cu)等离子体相互作用产生超热电子的能谱呈双温麦克斯韦分布,超热电子温度为81 keV,激光吸收的主导机制为真空吸收。     

超短脉冲激光与固体等离子体相互作用实验研究

实验研究了超短脉冲激光（744nm/120fs/12mJ）与固体（Cu）等离子体相互作用产生超热电子的能谱与角分布,利用电子磁谱仪与成像板（IP）探测器测量能谱,采用IP在入射平面内测量角分布。在无预脉冲、P极化激光45°斜入射下,采用Maxwellian分布拟合得到的超热电子温度为46keV,超热电子主要沿靶法线方向发射。产生超热电子的主导机制为真空加热,等离子体的电荷分离势约为70keV。     

激光波长对超热电子产生影响的实验研究

实验研究了两种波长超短脉冲激光(744 nm/120 fs/12 mJ、248 nm/420 fs/35 mJ)与固体(Cu)等离子体的相互作用,利用电子磁谱仪与成像板探测器测量了激光入射平面内超热电子的能谱与角分布.在无预脉冲、P极化激光45°斜入射的条件下,采用Maxwellian分布拟合得到的超热电子温度分别为46和19.4 keV,超热电子主要沿靶法线方向发射.产生超热电子的主导机制为真空加热,实验验证了真空吸收定标率Th≈4.11×10-2(Iλ2)1/2.54(keV).等离子体的电荷分离势分别为70和45 keV.     

激光靶耦合中受激Raman散射数值模拟研究和对腔靶实验的分析

利用一维半粒子模拟程序,对平面靶和腔靶密度标长的受激Ra-man散射(SRS)进行了数值模拟研究。得到了SRS的线性增长和非线性饱和的细致的物理图像,给出了热电子和超热电子的分布函数、热电子和超热电子温度T_e和T_h以及由SRS产生的超热电子的份额。还利用Raman散射谱推断和分析了等离子体次临界区的密度分布。这些理论结果与神光12号激光器上的SRS和超热电子实验结果合理地符合。     

IAPCM-0018 激光靶耦合中受激Raman散射数值模拟研究和对腔靶实验的分析

利用一维半粒子模拟程序,对平面靶和腔靶密度标长的受激Raman散射(SRS)进行了数值模拟研究。得到了SRS的线性增长和非线性饱和的细致的物理图像,给出了热电子和超热电子的分布函数、热电子和超热电子温度T_e和T_h以及由SRS产生的超热电子的份额。还利用Raman散射谱推断和分析了等离子体次临界区的密度分布。这些理论结果与神 光12号激光器上的SRS和超热电子实验结果合理地符合。     

强流负离子束系统的数值模拟研究

为了辅助设计下一代受控核聚变装置所要求的高能、大功率中性束注入器,我们根据负离子-中性束注入系统的特点,建立了数值模拟负离子束系统的物理模型和计算程序,并进行了数值模拟研究。与数值模拟正离子束系统的物理模型相比,该物理模型包含了更多的物理过程,如需要利用磁场来偏转与负离子一起引出的电子,以提高系统效率;为此就必须考虑等离子体电子横越磁场的扩散并包含由离了源等离子体引出的负离子和电子在电磁场共同作用下的运动行为以及相关等离子体参数对粒子初始发射的影响;也包含了束内部空间电荷非线性力和负离子在输运过程中的剥离损失等物理现象。在进行的数值模拟研究中,对系统的几何尺寸及电磁     

预脉冲对超短激光与薄膜靶相互作用加速产生质子的影响

采用波长为744 nm、聚焦功率密度为6×10¹⁶W/cm²的超短激光分别与两种不同厚度的铝薄膜靶相互作用,根据鞘层加速机制在靶后法线方向测量质子束角分布和能谱随靶厚度的变化,研究了预脉冲对质子加速的影响。随着薄膜靶厚度的降低,质子计数迅速增加,但当薄膜靶厚度太薄时,激光预脉冲形成的预等离子体影响了薄膜靶的面型,导致质子横向发散角迅速增加,而薄膜靶面型的破坏减少了激光与等离子体相互作用过程中的电子回流,从而降低了超热电子的产生和鞘层加速电场的维持,影响了质子的加速能谱。因此,超短脉冲激光与薄膜靶相互作用加速产生质子束,应尽量降低预脉冲,不能采用太薄的薄膜靶,以避免预等离子体影响薄膜靶的面型,导致质子的能量降低、发散角增大。     

超短超强激光与固体靶相互作用所致X射线剂量实验研究

超短超强激光与固体靶相互作用可产生显著的X射线剂量,其辐射防护问题是辐射防护和激光等离子体物理的学科交叉问题,对超短超强激光装置安全运行至关重要。为验证清华大学所提出的剂量评估公式,对超短超强激光与固体靶作用所产生的X射线剂量开展了实验研究。设计了用于屏蔽靶室内超热电子和散射光子的屏蔽结构,仅测量超热电子和固体靶作用所产生的X射线剂量,并开展蒙特卡罗模拟评估其屏蔽效果。基于星光 Ⅲ激光装置对不同激光功率密度（7×1018~4×1019 W/cm2）下不同角度上的X射线剂量开展了实验测量,并与不同的剂量评估公式结果进行了比较分析,实验中还对不同剂量测量探测器的响应进行了比较。计算结果表明,所设计的屏蔽结构能很好地屏蔽超热电子和散射光子。实验结果表明,清华大学所提出的剂量评估公式较文献公式能更好地与实验结果吻合。随激光功率密度的增加,前向的X射线剂量较侧向增加得更快。     

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.     

CBETor: a hybrid-kinetic particle-in-cell code for cross-beam energy transfer simulation

The parametric instability related to ion motion and the resulting cross-beam energy transfer are important aspects in the physics of inertial confinement fusion. The numerical simulation of the above physical problems still faces great technical challenges. This paper introduces a 2D hybrid-kinetic particle-in-cell (PIC) code, CBETor. In this code, the motion of ions is described by the kinetic method, the motion of electrons is described by the simplified fluid method and the propagation of laser in plasma is described by solving the wave equation. We use CBETor and the popular fully kinetic PIC code EPOCH to simulate the stimulated Brillouin scattering and cross-beam energy transfer process, respectively. The physical images are in good agreement, but CBETor can significantly reduce the amount of calculation. With the premise of correctly simulating the ion dynamics, our hybrid-kinetic code can effectively suppress the noise of numerical simulation and significantly expand the simulation scale of physical problems. CBETor is very suitable for simulating the physical process dominated by ion motion in the interaction of medium intensity laser and underdense plasma.     

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.     

Numerical studies on pair production in ultra-intense laser interaction with a thin solid-foil

A theoretical and numerical model of photon and electron–positron pair production in strong-field quantum electrodynamics(QED) is described. Two processes are contained in our QED theoretical model, one is photon emission in the interaction of ultra-intense laser with relativistic electron(or positron), and the other is pair production by a gamma-ray photon interacting with the laser field.This model has been included in a PIC/MCC simulation code named BUMBLEBEE 1 D, which is used to simulate the laser plasma interaction. Using this code, the evolutions of electron–positron pair and gamma-ray photon production in ultra-intense laser interaction with aluminum foil target are simulated and analyzed. The simulation results revealed that more positrons are moved in the opposite direction to the incident direction of the laser under the charge separation field.     

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.     

A Compact Fusion–Fission Hybrid Reactor

Up today, two hyper research projects to achieve nuclear fusion energy exist; inertial confinement fusion (ICF) driven by laser, called national ignition facility (NIF) and magnetic confinement fusion the international thermonuclear experimental reactor (ITER) project. In reaching the required temperature and pressure, to ignite nuclear fusion reactor, is technologically complex and economically expensive. Thus, a breakthrough and a short cut, other alternative methods should be considered. Pulsed power ICF driver with repetitive pulse operation, mainly dense plasma focus (DPF) machines for high yield fusion neutrons could be taken as drivers for the fission blanket operation. The setup can be a cost-effective and efficient. In this article, we consider a set of two medium energy sizes DPF to produce simultaneously dense plasma columns, operating as thermonuclear plasma driver, to pierce the pellet target for external nuclear fusion reactions. These DPFs produce sufficient fast neutrons for the fission process in the neutral uranium or thorium and/or weak enriched uranium blanket. The drive systems and the concept for delivering thermonuclear plasma to pellets target in the magnetic free zone of central region will be presented. The feasibility of such fusion–fission hybrid reactor will be discussed.     

Multi-Material ALE with AMR for Modeling Hot Plasmas and Cold Fragmenting Materials

We have developed a new 3D multi-physics multi-material code,ALE-AMR,which combines Arbitrary Lagrangian Eulerian(ALE) hydrodynamics with Adaptive Mesh Refinement(AMR) to connect the continuum to the microstructural regimes.The code is unique in its ability to model hot radiating plasmas and cold fragmenting solids.New numerical techniques were developed for many of the physics packages to work efficiently on a dynamically moving and adapting mesh.We use interface reconstruction based on volume fractions of the material components within mixed zones and reconstruct interfaces as needed.This interface reconstruction model is also used for void coalescence and fragmentation.A flexible strength/failure framework allows for pluggable material models,which may require material history arrays to determine the level of accumulated damage or the evolving yield stress in J2 plasticity models.For some applications laser rays are propagating through a virtual composite mesh consisting of the finest resolution representation of the modeled space.A new 2nd order accurate diffusion solver has been implemented for the thermal conduction and radiation transport packages.One application area is the modeling of laser/target effects including debris/shrapnel generation.Other application areas include warm dense matter,EUV lithography,and material wall interactions for fusion devices.     

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.     

中性束注入快离子初始分布的蒙特卡罗模拟

比较精确地模拟计算中性束注入（NBI）托卡马克等离子体的快离子初始分布是采用大规模数值模拟方法研究NBI快离子相关物理问题的首要任务。本文建立了NBI托卡马克等离子体的简化物理模型,采用蒙特卡罗方法自主开发了NBI应用程序。选取ASDEX Upgrade（AUG）托卡马克上切向注入和垂直注入两种情况为计算实例,分别模拟计算出NBI粒子被离子化的初始三维空间位置,并统计得出初始快离子的径向分布、极向角分布、环向角分布和投掷角分布,这些计算结果与国际上相关文献结果一致。     

Numerical Modeling of a Magnetic Flux Compression Experiment

A possible plasma target for Magnetized Target Fusion (MTF) is a stable diffuse z-pinch in a toroidal cavity, like that in MAGO experiments. To examine key phenomena of such MTF systems, a magnetic flux compression experiment with this geometry is under design. The experiment is modeled with 3 codes: a slug model, the 1D Lagrangian RAVEN code, and the 1D or 2D Eulerian Magneto-Hydro-Radiative-Dynamics-Research (MHRDR) MHD simulation. Even without injection of plasma, high-Z wall plasma is generated by eddy-current Ohmic heating from MG fields. A significant fraction of the available liner kinetic energy goes into Ohmic heating and compression of liner and central-core material. Despite these losses, efficiency of liner compression, expressed as compressed magnetic energy relative to liner kinetic energy, can be close to 50%. With initial fluctuations (1%) imposed on the liner and central conductor density, 2D modeling manifests liner intrusions, caused by the m = 0 Rayleigh-Taylor instability during liner deceleration, and central conductor distortions, caused by the m = 0 curvature-driven MHD instability. At many locations, these modes reduce the gap between the liner and the central core by about a factor of two, to of order 1 mm, at the time of peak magnetic field.