飞秒强激光与团簇相互作用产生高能离子和中子的研究
文献类型：学位论文
| 作者 | 李洪玉 |
| 学位类别 | 博士 |
| 答辩日期 | 2008 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐至展 |
| 关键词 | 飞秒强激光脉冲 同核和异核气体团簇 库仑爆炸 等离子体细丝 激光驱动核聚变 |
| 其他题名 | Study on the Generation of Energetic Ions and Neutrons in the Interaction of Femtosecond Intense Laser Pulses with Clusters |
| 中文摘要 | 超强超短激光与原子、分子、电子以及等离子体等形态物质在极端条件下的高度非线性相互作用研究是当今强场物理的重要前沿研究领域。随着强场物理、团簇科学以及激光技术的迅猛发展，超强激光场（>1015 W/cm2）与团簇（通常是指大尺寸气体团簇）之间的相互作用已经成为强场超快激光物理领域的一个重要研究发展方向。作为介于气体原子、分子与固态之间的一种过渡形态，团簇兼有气体靶和固体靶的优点，研究飞秒强激光与团簇的相互作用对深入揭示强激光与物质相互作用的物理图象及其规律有着重要的意义。超强超短激光与团簇相互作用能产生能量高达兆电子伏量级的高能离子以及非常强的X射线辐射等，这对激光核聚变和X射线激光等领域的研究也会产生影响。 本论文从理论上研究了超强超短激光与团簇相互作用产生高能离子和中子的过程，研究成果主要包括以下四个方面： 1. 提出一个简化的库仑爆炸模型，研究了飞秒强激光脉冲辐照氢团簇发生爆炸产生的质子动能与激光强度、脉冲宽度及团簇尺寸的关系，发现只有当团簇尺寸与激光参数相匹配时才能获得最大质子动能。通过加入对团簇尺寸分布和激光焦斑强度分布的考虑，数值模拟计算的质子能谱和质子能量相对于光强的饱和效应与实验测量结果达到了较好的吻合，这表明此模型对于定性与定量地研究超短强激光脉冲与氢团簇相互作用都是有效的。 2. 在考虑团簇对激光能量吸收的基础上，建立模型研究了激光与氘团簇喷流作用产生等离子体细丝激发的核聚变反应，估算了从相邻团簇产生的高能氘核碰撞引发的核聚变（团簇间核聚变，intercluster fusion）和高能氘核与周围冷气体中的低能氘原子碰撞引发的核聚变（束靶核聚变，beam-target fusion）产生的中子产额，发现中子产额是与激光和团簇的参数（如激光能量、聚焦半径、聚焦位置、团簇尺寸等）密切相关的，只有两者的参数达到最佳匹配，才能获得最大中子产额。 3. 采用改进的库仑爆炸模型，系统研究了异核团簇库仑爆炸动力学过程中两种赶超效应的产生条件。首次提出了一个以重离子和轻离子的初始电荷密度之比表征的竞争参数ζ =ρBqB/ρAqA，用于判断异核团簇库仑爆炸过程中内层轻离子能否赶上并超越外层轻离子的赶超效应。若重离子的电荷密度高于两倍的轻离子电荷密度（即ζ>2），团簇内层的轻离子就可以赶上外层的轻离子形成一个冲击壳层，从而有可能驱动在单个氘代异核团簇内部发生氘氘核聚变。通过对中子产额的估算发现，由于异核团簇爆炸过程中可能发生的两种赶超效应将使氘核获得的能量更高、氘核分布在高能区域的数目更多，因此在提高激光加热团簇产生核聚变中子产额方面，氘代异核团簇相对于纯氘团簇是一个更好的候选作用对象。 4. 采用三维粒子动力学模拟方法，研究了甲烷/氘代甲烷团簇在强场中的非纯库仑爆炸动力学行为。甲烷/氘代甲烷团簇在超短强激光脉冲辐照下发生膨胀，大量质子/氘核超越慢速膨胀的碳离子从而形成两个分离的子团簇。强激光场作用下，氘核动能随团簇尺寸的增大而增加；随激光光强的增加、脉宽的减小而增大；负啁啾激光脉冲加热氘代甲烷团簇获得的氘核动能最高，无啁啾次之，正啁啾对应的氘核动能最小。 |
| 英文摘要 | The research of highly nonlinear interaction between ultra-intense ultra-short lasers and matters, such as atoms, molecules, electrons and plasmas, is one of the most important frontiers in the high-field physics. Especially, with the advanced progresses in high-field physics, cluster physics and intense laser technology, the interaction of ultra-intense lasers (higher than 1015 W/cm2) with clusters (generally with large size) has become an important developmenting aspect in the research field of ultra-intense ultra-fast laser physics. As bridge state from atoms, molecules to bulk solid, clusters have the unique advantage combining gases and solids. The study on the interaction of femtosecond intense laser pulses with clusters is very important to unveil the comprehensive micro and macro physical picture about the nature of intense laser-matter interaction. Clusters irradiated by intense laser pulses can generate MeV ions and intense X-rays, which will influence the research of laser-induced nuclear fusion and table-top X-ray laser, etc. In this thesis, some theoretical investigations on the production of energetic ions and neutrons in the interactions of femtosecond intense laser pulses with clusters have been carried out. The main work is given as follows: 1. By employing a simplified Coulomb explosion model, the explosion dynamics of hydrogen clusters driven by an ultrashort intense laser pulse has been analyzed analytically and numerically. The dependence of average and maximum proton kinetic energy on cluster size, pulse duration, and laser intensity has been investigated respectively. The existence of an optimum cluster size allows the proton energy to reach the maximum when the cluster size matches with the intensity and the duration of the laser pulse. In order to explain our experimental results such as the measured proton energy spectrum and the saturation effect of proton energy for the laser intensity, the effects of cluster size distribution as well as the laser intensity distribution on the focus spot should be considered. Good agreement between simulations and measurements indicates that this model is effective for the study of the interaction of ultrashort intense laser pulses with hydrogen clusters not only qualitatively but also quantitatively. 2. Taking the attenuation of laser intensity into account due to the laser energy absorption by clusters, a model is proposed to study the nuclear fusions inside the generated hot plasma filament when the intense laser pulses heat up the deuterium cluster jet. The neutron yield produced in the intercluster fusion which occurs among fast deuterons from expanding neighbor clusters, and beam-target fusion which occurs between these energetic deuterons and cold deuterium atoms inside the surrounding gas, are roughly estimated. It is found that the neutron yield depends on the laser-cluster parameters such as the cluster size, the laser energy, the focal spot radius and position. Only these parameters match with each other, can the neutron conversion rate or the neutron yield be maximized. 3. Two overrun effects in the Coulomb explosion dynamics of heteronuclear clusters have been investigated theoretically by use of a revised Coulomb explosion model. If the charge density of heavy ions is twice higher than that of light ions, i.e. a proposed competitive parameter(which is represented as the ratio of the initial charge density of heavy ions to that of light ions) ζ =ρBqB/ρAqA>2, the inner light ions can overtake those light ions on the surface of the cluster and form a shock shell during the explosion, which might drive the intracluster collision and fusion of light ions. Our analysis indicates that because both a higher energy region and a higher proportion of deuterons distributing in the high energy region can be created in the deuterated heteronuclear clusters, deuterated heteronuclear clusters are a better candidate compared with homonuclear deuterium clusters for increasing the total fusion yield. 4. The simulations of three-dimensional particle dynamics are carried out to investigate the non-pure Coulomb explosion dynamics of methane and deuterated methane clusters under the irradiation of an ultrashort intense laser pulse. It is indicated that as the cluster expands, the majority of protons/deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subclusters. With the intense laser irradiation, the deuteron energy increases with the increase of the cluster size and laser intensity, but with the decrease of the laser pulse width. The deuteron energy obtained from the intense laser pulses with negative chirp is found to be larger than that with positive chirp. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15568]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 李洪玉. 飞秒强激光与团簇相互作用产生高能离子和中子的研究[D]. 中国科学院上海光学精密机械研究所. 2008. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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