重离子束驱动的高能量密度物理数值模拟及动态真空研究

发布时间：2018-04-29 23:33

本文选题：强流重离子束 + 束靶相互作用　；参考：《中国科学院研究生院(近代物理研究所)》2016年博士论文

【摘要】：高能量密度物质广泛存在于宇宙星体中,且是惯性约束聚变所必经的极端物质状态,实验上对高能量密度物质物理性质的研究不仅对天体物理意义重大,同时也是惯性约束聚变研究中拟解决的的关键科学问题。重离子束由于其特殊的能量沉积方式,作为驱动源为高能量密度物理实验研究开辟了一条新道路。国际大科学工程FAIR及HIAF已将强流重离子束驱动的高能量密度物理列为科学目标之一。目前FAIR已经处于工程建设中,而HIAF工程项目也已获批,将要启动,所以相关数值模拟计算工作必须先行一步为加速器工程建设及实验方案提供科学及技术参考。本论文中选取高能量密度物理前期研究中的两个关键问题进行了深入的研究及讨论,分别是高能量密度物理终端的束靶相互作用模拟及加速器建设过程中的动态真空问题。除此之外,本论文中还对重离子与固体相互作用过程中的微观机制做了深入研究。具体研究内容及主要结果如下:1、系统性地定量地研究了强流重离子束与靶相互作用过程中束流的能量,束斑,脉宽以及靶的结构对产生的高能量密度物质状态的影响,结果表明:束流直接加热靶物质时,物质中可以达到的温度与单位沉积能量几乎呈线性关系;物质的流体运动大约开始在束流加载后的几十个ns内,所以束流脉宽超过一百ns会影响束流的沉积效率;采用不同的束靶耦合方案可以满足我们对高能量密度物质状态的各种需求,比如若想在物质中产生极高压状态,环形空心束作用双层靶外层对内层材料进行低熵压缩是首选,可以将物质密度进行上百倍压缩;若想产生极高温状态,可采用圆斑束加热双层靶,内层材料在束流直接加热以及外层冲击波压缩共同作用下生成极高温状态。2、针对HIAF提出的束流参数,模拟了三种典型的束靶耦合结构下所产生的极端物质状态,结果表明:利用HIAF一期工程项目B-Ring(400ns脉宽)提供的束流,实验上虽然可以产生高能量密度物质,但是模拟计算表明靶被最优压缩的时刻处于束流脉宽内一百多纳秒,意味着多一半的束流没有被有效利用,而如果将束流压缩至50ns,实验上的物质状态参数可以被提高一个量级,这样实验上很有可能会达到高能量密度物理的强冲击波区域;二期工程C-Ring一旦建成,实验上冲向高能量密度物理的强辐射区域也是非常有希望的。3、以FAIR工程为例,模拟估算了强流重离子束作用下靶的气化过程引起的终端动态真空变化,通过在现有束线上对压力波传输进行测量校准了动态真空蒙特卡罗模拟程序。结果显示:FAIR工程高能量密度物理终端现有设计无法抵挡靶的气化对真空的影响,对整个加速器是一个安全隐患,但是模拟结果给出的气化压力波传输所需的时间量级提供了解决方法,即在终端连接处附件安装一个毫秒量级快阀。4、超高真空环境下加速器环内的残余气体与束流作用导致束流偏转与管壁碰撞,同时释放更多残余气体这一效应使重离子束单脉冲离子数无法超过109,为了解决这一难题,GSI-SIS18利用一个准直器降低离子与管壁碰撞中解吸至真空中的粒子数目将束流强度提高了一个量级,本文介绍了针对FAIR-SIS100的低温准直器研究,初步实验测量结果显示发现低温条件下,物质的行为与常温下完全不同,这一方面还需要再进一步的研究。5、实验上测量了高电荷态离子与固体(Z=14-79)相互作用过程中的X射线发射,分析发现炮弹离子X射线发射产额随靶原子序数变化呈周期性震荡结构,近能级匹配区域碰撞系统中X射线发射存在非常明显的电荷态效应,这些都表明了能级匹配区域分子轨道跃迁机制的重要性。基于观测到的电荷态效应及分子轨道跃迁理论,推出了高电荷态离子在固体中的平衡时间约7fs。
[Abstract]:High energy density material exists widely in cosmic stars, and is an extreme material state which is required by inertial confinement fusion. The study of physical properties of high energy density materials is not only important to astrophysics, but also the key scientific problem to be solved in the study of inertial confinement fusion. Heavy ion beam is due to its special characteristics. The energy deposition method, as the driving source, has opened a new road for the physical experiment of high energy density. FAIR and HIAF have listed the high energy density physics of the heavy ion beam driven by the strong current and heavy ion beam as one of the scientific goals. At present, the FAIR has been in the engineering construction, and the HIAF project has also been approved, so the phase will be started. In this paper, two key problems of high energy density physics are studied and discussed in this paper, which are the simulation of the beam target interaction of high energy density physical terminals and the construction of the accelerator. In addition, the microscopic mechanism of the interaction between heavy ions and solid is also studied in this paper. The main results are as follows: 1, the beam energy, beam spot, pulse width and target junction in the interaction process of strong current heavy ion beam and target are systematically studied. The effect of the structure on the state of high energy density material shows that when the beam is directly heated, the temperature can be almost linear with the unit deposition energy, and the fluid movement of the material begins in the dozens of NS after the beam loading, so the beam pulse width over one hundred ns will affect the deposition efficiency of the beam. By using a different beam target coupling scheme, we can meet various requirements for the state of high energy density material. For example, if we want to produce extremely high pressure state in the material, the low entropy compression of the inner layer is the first choice for the double layer target outer layer of the annular hollow beam, and the density of the material can be compressed by 100 times, and if we want to produce very high temperature state, A circular spot beam can be used to heat double layers of target, and the inner material generates extremely high temperature state.2 under the joint effect of beam direct heating and external shock wave compression. According to the beam parameters proposed by HIAF, the extreme material state produced by three typical beam target coupling structures is simulated. The results show that the HIAF phase I project B-Ring (400ns pulse) is used. The beam provides a high energy density material in experiment, but the simulation results show that the optimal compression time of the target is more than 100 nanoseconds in the beam pulse width, which means that more than half of the beam is not used effectively, and if the beam is compressed to 50ns, the actual state parameters of the material can be improved by one order of magnitude. A strong shock wave region with high energy density physics is likely to be reached in the sample experiment; once the two project C-Ring is built, the strong radiation area of high energy density physics is also a very promising.3. Taking the FAIR project as an example, the dynamic vacuum change of the terminal caused by the gasification process of the target under the action of the heavy ion beam is simulated. The dynamic vacuum Monte Carlo simulation program is calibrated by measuring the pressure wave transmission on the existing beam line. The results show that the existing design of the FAIR engineering high energy density physical terminal can not resist the effect of the gasification of the target on the vacuum, and it is a safety hazard to the whole accelerator, but the pressure wave transmission given by the simulation results is given. The required time magnitude provides a solution to the installation of a millisecond fast valve.4 at the terminal attachment. The residual gas and beam flow in the accelerator ring causes the beam deflecting to collide with the tube wall in the ultra high vacuum environment, and the release of more residual gases can not exceed 109 of the single pulse ion number of the heavy ion beam. In order to solve this problem, GSI-SIS18 uses a collimator to reduce the number of particles in the collision between the ion and the tube wall. The intensity of the beam is increased by one order. This paper introduces the study of the low temperature collimator for FAIR-SIS100. The preliminary experimental results show that the behavior of the matter at low temperature is completely different from the normal temperature. In this respect, we also need to further study.5, experimentally measuring the X ray emission from the interaction between highly charged ions and solid (Z=14-79). The analysis shows that the X ray emission yield of the projectile ions is periodically oscillating with the change of the number of target atoms, and the X ray emission of the near energy level matching region collision system is very bright. The significant charge state effect shows the importance of the molecular orbital transition mechanism in the energy level matching region. Based on the observed charge state effect and the molecular orbital transition theory, the equilibrium time of the highly charged ions in the solid is about 7fs.

【学位授予单位】：中国科学院研究生院(近代物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O572

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