激光等离子体相互作用中电子输运和成丝不稳定性研究
文献类型：学位论文
| 作者 | 白亚锋 |
| 文献子类 | 博士 |
| 导师 | 刘建胜 |
| 关键词 | Weibel不稳定性，Particleincell，电离前端不稳定性，实验室天体物理 Weibel instability, Particle in cell, intability of the ionization front, laboratory astrophysics |
| 其他题名 | Electron transport and current filament instability in laser-plasma interaction |
| 英文摘要 | 随着超强超短激光技术的发展，高能量密度物理作为一个新的学科逐渐成为国际上研究的热点。在传统的惯性约束聚变中，通过激光均匀辐照球形靶丸产生高温高压条件，实现聚变燃料的点火。由于聚变过程的复杂性，靶丸的内部结构以及靶丸压缩的对称性等对点火成败起到了关键的作用。在快点火中通过点火脉冲在预压缩靶的临界面处驱动强流电子将能量输运到靶丸核心，从而实现点火。由于电子在等离子体中输运过程的复杂性，电子在靶丸核心能量的沉积受到很多因素的影响。强流电子在等离子体中的输运过程非常复杂，值得深入研究。强激光激发的强流电子会诱导兆高斯量级的强磁场，强磁场的产生方法有很多种，其中一种是由于电子束-等离子体系统能量的异向性，这时电子束-等离子体系统是不稳定的，电子束在传输过程中撕裂成丝，产生强磁场。这种强磁场不仅在点火物理中意义重大，在天体物理中这种强磁场与gamma射线暴的形成密切相关，通过激光产生的高能量密度物理环境为实验室天体物理提供了非常理想的实验平台。 本论文通过实验和理论等多种研究途径相结合，对超强超短激光与物质的相互作用，高能电子在等离子体中的输运等过程进行了研究。实验中观测到了电子束在电离前端的不稳定传输以及电子束的分裂成丝等现象，理论和模拟成功地解释了这些实验观测结果。本文主要取得的结果如下： 1. 实验研究了激光与镀有铝膜的电介质靶材的相互作用，在SiO2内部观测到了以激光焦点为中心各向同性的电离云。电离云的形成与束流电子以及离子的碰撞电离有关，实验结果与理论模型相符。通过直边衍射条纹的移动分析了电子密度分布，发现在电离前端电子密度出现凹槽，凹槽的产生与电子束在绝缘体中的不稳定性输运有关。 2. 激光物质相互作用中强电流的出现预示着强磁场的产生，通过法拉第旋转法我们在SiO2靶材表面附近观测到强磁场，通过理论方法对磁场的时间和空间演化进行建模，得到了与实验符合的结果。这些结果对超强超短激光与物质相互作用中的磁场产生以及与之相关的领域如快点火，实验室天体物理等至关重要。 3. 在实验上将电子束导引至热膨胀等离子体系统中，对电子束经过不同标长等离子体的束斑状态进行测量。发现了电子束斑出现了成丝的迹象，并且丝状结构随等离子体标长的变化而变化，这一实验结果对实验室天体物理，离子加速，快点火，等相关领域具有重要的参考价值。 4. 作为研究组主要成员在实验中利用飞秒强激光驱动金属丝波导螺旋波荡器实现了强THz辐射。实验中，通过超强超短激光辐照金属丝靶打出电子束，在丝靶表面形成瞬态径向电场。打出的电子束在径向电场中做螺旋运动产生强THz辐射，能量的转化效率超过百分之一。; The availability of ultra-short, super-intense laser beams make High Energy Density Physics one of the hottest topics in the world today. In the concept of traditional inertial confinement fusion, a small pellet is illuminated to compress the fuel in the core to ignition. Due the complexity of the ignition process, the structure of the ignition pellet, symmetries to illuminate the target and so on are major difficulties to realize the ignition. In fast ignition, an intense ignition beam is reflected and absorbed in the critical density layer of the precompressed target. Hot electrons are induced in the critical layer and propagate into the core of the pellet and energy is deposited there. Intense plasma return current can be induced due to charge conservation. This kind of systems is unstable and is subject to filamentation instability. The intense magnetic field can trap the hot electrons and influence the energy deposition process. Countless experiments are devised to understand this process. The intense magnetic field induced by filamentation instability is believed to be of key importance in various high-energy astrophysical phenomena, such as the gamma-ray burst produced in compact object mergers or collisions, or during the death of massive stars. The gamma-ray burst is closely related to collisionless shock formation, non-thermal electron acceleration, strong magnetic field amplification, and synchrotron/jitter radiation of the electron beam in an intense turbulent magnetic field. In this essay, the physics of laser matter interaction and many relevate subjects such as the propagation of hot electron in dense plasma are studied. The unstable propagation of intense electron beam in a dielectric target as well as the filamentation of hot electron beam in a hot preplasma are observed. This thesis includes the following innovative results: 1. The propagation of laser-driven fast electron beams inside a dielectric target is studied with the ultrafast shadowgraphy method. In the experiment, an ionization sphere expanding with a speed greater than the speed of sound is observed in the target. The edge diffraction fringes near the surface of the target are distorted which is thought to be due to the unstable propagation of the hot electron beam inside the target. A simplified three-dimensional model is proposed to analyze the underlying physics. 2. The intense electron beam induced in laser plasma interaction can produce intense magnetic field and is observed with the Faraday rotation method. The rotation angle changed greatly and lasted ~2 ps after the illumination of the pump pulse. The experimental results may imply an azimuthal magnetic field near the target front surface. An analytical model is developed to explain the experimental observation. 3. In the interaction between an energetic electron beam and a laser-irradiated insulated target, the combined action of corrugation and Weibel instabilities was observed. The electron beam split into current filaments owing to the current filament instability (CFI) when the prepulse is on. Nearby current filaments attract each other and merged when the time delay between the two beams (the prepulse and the electron beam) was greater than 1ps. The characteristic filamentary structure disappeared for time delays greater than 3 ps. This was due to the nonlinear evolution of the current filament instability. 4. Intense THz radiation is observed in the interaction between a femtosecond laser pulse and a metal wire. The wire is charged while electron beam is emitted from the surface and is guided to move with a helical orbit. Intense THz radiation is emitted in this process. The conversion efficiency of laser light to THz radiation to greater than 1% thus is a new potential method for intense THz radiation. |
| 学科主题 | 光学 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31127]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 白亚锋. 激光等离子体相互作用中电子输运和成丝不稳定性研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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