【作者】 陈实；

【导师】 李剑峰；

【作者基本信息】 中国工程物理研究院 ， 光学， 2013， 博士

【摘要】 高能量密度物理是近年来物理学领域的一个研究热点。人们对高能量密度物理这一领域在理论上有了更深入的认识,具备了在实验室中产生某些处于高能量密度状态的实验对象的能力,对于其中发生的物理过程可以进行各种探测和诊断,并且利用在实验室中得到的数据和结论推测某些发生在遥远宇宙中的天体物理过程。对高能量密度物理的研究不仅在基础科学研究方面有重要意义,而且在应用方面也展现出巨大的潜力。从热力学和统计物理的角度看,高能量密度系统的一个重要特征是往往处于非平衡的状态。在这样的条件下,系统往往会产生出一定的结构或者模式。这种结构或者模式的产生及其演化是高能量密度系统中普遍存在的现象,对这一现象的理解对于我们认识高能量密度物理过程是重要的。因此,本文针对高能量密度条件下等离子体系统磁场结构的产生、界面电荷密度调制模式的选择以及这些结构产生的效应等问题开展了探索性的工作,希望能够加深对这些物理过程的理解,为未来的研究工作提供参考。具体的研究工作和主要结论如下：1、讨论了高能量密度条件下等离子体系统自发地产生磁场结构的可能性。利用准静态模型进行了量纲分析和量级上的估算；利用动力学模型讨论了高能量密度条件下等离子体系统对内部统计涨落的响应过程。通过定性的量纲分析和半定量的模型方程求解,我们得到了等离子体系统发生自发磁化过程的温度—密度相图。相图的得到说明至少在理论上这一过程的发生是可能的。利用得到的结果初步分析了目前宇宙中存在的常见的磁场结构,对宇宙大尺度磁场结构的产生给出了一定的解释,对宇宙早期暴胀过程与宇宙大尺度磁场结构的关系进行了初步的分析,给出了一种新的解释暴胀能量来源的模型。2、讨论了高能量密度条件下等离子体界面的模式选择问题。首先采用最小作用量原理和变分法,分析了一维电子体系在高能量密度条件下的状态及演化过程。认为电子密度调制状态是基本的运动模式,以调制的幅度和空间波长作为广义坐标,通过能量守恒和受力平衡得到系统的运动方程,得到了调制振幅和空间波长随时间演化的关系。然后利用等离子体的流体力学方程,采用模式选择的本征模方法,在二维情况下讨论了界面模式选择过程,得到了界面电荷密度调制模式的色散关系。3、讨论了高能量密度条件下等离子体系统结构或者模式对于某些特定物理过程所产生的效应问题。对于超短超强脉冲激光辐照金属丝产生高能电子束的过程,通过理论分析和经典轨迹蒙特卡罗数值模拟的方法讨论了磁场结构对于电子束发散度的影响。结果表明高能电子束自身磁场对于其聚焦效应有不可忽略的贡献。在同时考虑了电场和磁场作用的情况下得到的电子束发散度可以较好地解释实验结果。对于斜入射强X射线辐照金属靶的过程,从理论上讨论了在界面产生超光速运动的Compton电流这一界面模式的可能性,并且讨论了该电流产生的电磁脉冲辐射。理论分析的结果表明金属靶表面的Compton电流可以产生强电磁辐射,并且这种机制在强X射线辐照条件下可能是产生电磁辐射的主要机制。更多还原

【Abstract】 Recently, high-energy-density physics (HEDP) has become an active area of research that receives considerable attentions. Progresses in theories have cast new lights on many HED phenomena. Developments in experimental techniques, such as ultra-intense lasers, pulsed power techniques and various advanced di-agnostics, enable us to create certain HED systems in laboratories, to detect processes occurred under HED conditions, and to estimate physical mechanisms responsible for some astrophysical phenomena far away in the universe. High-energy-density physics research has no only scientific significance, but also po-tentials of future applications. From the view of thermal and statistical physics, one important characteristic of HED systems is that they are usually under non-equilibrium conditions. Structures or modes often appear in systems under such conditions. Since the appearance of structures and modes is a common phe-nomenon in high-encrgy-density systems, investigation in this phenomenon is of considerable importance to get a deeper understanding of HED processes.Based on the reasons mentioned above, in this thesis we study the spon-taneous magnetization and surface charge density modulation mode selection processes in plasmas under high-energy-density conditions, as well as the effects of such structures and modes on relevant HED processes. We hope to provide new insights for certain HEDP problems and reference in relevant researches. The main topics and results contained in this thesis are as follows:1. The possibility of spontaneous magnetization in plasmas under high-energy-density conditions has been discussed. A quasi-static model is developed for qualitative calculations. By using a dynamic model, we investigated the responses of HED plasmas to interior statistical fluctuations. The temperature-density phase diagram for spontaneous magnetization of plasmas is obtained through these qualitative calculations and quantitative solutions of model equa-tions, indicating that the spontaneous magnetization process is possible, at least theoretically. Further more, we discussed the appearance of common cosmic magnetic fields and proposed a novel explanation for the origin of the large-scale magnetic field structures in the universe. We also discussed the relation between the inflation phase and the cosmic magnetic fields and gave a new energy source for the inflation.2. The mode selection of plasma surface under high-energy-density condi-tions has been investigated. We first discussed the evolution of one-dimensional electron systems under HED conditions by the least-action principle and variation method. Assuming that charge density modulations are basic modes and choos-ing the amplitude and spatial wavelength of these modes as general coordinates, we obtained the equations of energy conservation and force balance. Numerical solving these equations gives the temporal dependence of amplitude and spatial wavelength of the modes. We also discussed the mode selection of plasma surface in two-dimensional case, using fluid equations of plasma and eigen-mode method. The dispersion relations of surface charge density modulation modes have been obtained.3. The effects of structures or modes of high-energy-density plasmas on certain processes have been researched. In the case of generation of electron beams through ultra-intense laser-plasma interaction, we discussed the effect of magnetic field on the divergence of electron beams through theoretical analysis and classical trajectory Monte Carlo simulations. Results show that self magnetic field of electron beams has non-negligible influence on the their divergence. After including both electric and magnetic field in our consideration, our results are in good agreement with experiments. In the case of oblique incident intense x rays on metallic targets, we discussed the possibility of the generation of surface Compton current density, as well as electromagnetic pulse due to this current density. Theoretical analysis reveals that such surface Compton current density could generate strong electromagnetic pulses, and this mechanism might be of considerable importance in the generation of electromagnetic pulses.更多还原