【作者】 刘勇；

【导师】 刘三秋；

【作者基本信息】 南昌大学 ， 材料物理与化学， 2011， 博士

【摘要】 随着激光强度不断提高、激光惯性约束核聚变实验技术不断进步以及激光天体物理实验的深入开展,相对论激光与等离子体的相互作用正越来越受到人们的关注。从理论上研究相对论激光等离子体和相对论激光与正负电子等离子体的相互作用有助于激光惯性约束核聚变快点火的实现以及实验激光天体物理的开展。本论文首先从李晓卿等人基于动力论得到的相对论激光等离子体中自生磁场的控制方程出发,通过微扰法得到了横扰动的色散方程。从该色散方程得到了特定的条件下最大增长率和与之相应的特征尺度的解析结果。考虑到色散方程的复杂性,我们进行了数值计算。计算结果与实验和数值模拟的结果一致。并且发现,解析结果是数值计算结果很好的近似,可以用之来估算相对论激光等离子体中自生磁场的增长率和特征尺度。其次,考虑到自生磁场控制方程能够自洽的描述高频横等离激元、离声运动和自生磁场的非线性演化,通过数值计算得到了静态极限下电场包络、自生磁场和密度空穴的演化图像。研究发现自生磁场的最大强度与激光本身的振荡磁场为同一量级,而密度空穴的排空率则可达到72%。自生磁场的出现与电场包络的强度和不均匀性相关,正是由于密度空穴中俘获了极强、极不均匀的横等离激元场,磁场才囿于密度空穴中。密度空穴中既存在超强包络电场,又存在超强的磁场。这种腔子结构对于高能粒子的产生,以及准直有着重要的作用。然后,基于李晓卿等人横等离激元动力学理论得到了极端相对论等温正负电子等离子体中相对论激光脉冲的非线性演化的控制方程。基于该方程研究发现,对于一维的线偏振激光而言,在非线性相互作用过程中由于调制不稳定性可形成稳定的孤子结构；考虑到一维结构与三维可能存在显著不同,通过线性分析得到了三维情况下激光脉冲的调制不稳定性的最大增长率和相应的特征尺度；虽然一维存在稳定的结构,但是从标度定律和维里定律可知,三维电磁包络场由于调制不稳定性将坍塌,在场的坍塌过程中场强不断增强,最终形成小尺度的局域结构的强场。讨论了在激光等离子实验中观测到这样一种结构的可能性,以及与脉冲星辐射微脉冲的关联。最后,基于李晓卿等人横等离激元动力学理论得到了相对论激光脉冲与极端相对论非等温正负电子等离子体相互作用中自生磁场的非线性控制方程。从该方程通过线性分析得到调制不稳定性导致的自生磁场的增长率和特征尺度,并讨论这样一种机制在天体物理方面的应用。更多还原

【Abstract】 With the increase of laser intensity, the development of laser inertial confusion technology and the progress of laser astrophysics experiment, there is increasing interest on relativistic laser plasma interaction. Theoretical investigation on relativistic laser plasmas and the interaction of laser pulse with electron-positron plasmas is conducive to the realization of laser inertial confusion and the development of laser astrophysics experiment.Firstly, from the governing equations for self-generated magnetic field in relativistic laser plasma interactions, which are obtained by Li Xiao-Qing et al., the dispersion equation for transverse perturbation is obtained by small perturbation method. The analytical solution for the maximum growth rate and the corresponding characteristic scale of spontaneous magnetic field is derived under given conditions within the framework of the dispersion equation. Concerning the complexity of the dispersion equation, the numerical calculations are performed. The numerical results are consistent with those obtained from experiment and numerical simulation. In addition, the analytical results are pretty good approximation for numerical ones, thus, one can use them to estimate the scale of spontaneous magnetic field.Secondly, concerning the governing equations for self-generated magnetic field can self-consistently describe the nonlinear evolution of high frequency transverse plasmons, ion acoustic motion and spontaneous magnetic field, the temporal evolution of the envolope of electric field, spontaneous magnetic field and density caviton is given by numerical calculation under static limit. It shows the maximum amplitude for magnetic field is of the order of the laser oscillating magnetic field, and the density depletion would come to 72%. The self-exited magnetic field depends on the intensity and inhomogeneity of the envelope of electric field. The reason why magnetic field is confined in density caviton is due to density caviton captured extremely strong and inhomogeneous transverse plasmons. Such a caviton structure is important for the production of collimated energetic particles.Consequently, the nonlinear governing equations for the interaction of relativistic laser pulse with ultra-relativistic isothermal electron-positron plasmas are obtained on the basis of the kinetic theory for transverse plasmons established by Li Xiao Qing et al. From the governing equation, one can find there will be stable solitary structure when one dimensional linear polarized laser pulse interacts with the ultrarelativistic isothermal electron-positron plasmas. Considering the difference between one dimensional structure and three dimensional one, the modulation instability for three dimensional case is investigated, the maximum growth rate and the corresponding characteristic scale for the envelope electric field are derived. Although there is stable structure in one dimensional case, yet from scale law and virial theorem one can see three dimensional electric field envelope will collapse for modulation instability. During the collapse process, the increase of wave field strength leads to the formation of density caviton with strong localized field. The possibility of creating the structure in the laser electron-positron plasma interactions, and the correlation to the pulsar micro-pulse radiation are discussed.Finally, from the kinetic theory for transverse plasmons established by Li Xiao Qing et al., the nonlinear governing equation for self-generated magnetic field by the interaction of relativistic laser pulse with ultra-relativistic nonisothermal electron-positron plasmas is obtained. Based on the nonlinear equations, the growth rate and characteristic scale for spontaneous magnetic field are obtained from linear analysis. And the possible application of the mechanism to explain the generation of small scale magnetic field in astrophysical environments is proposed.更多还原