【作者】 王洪建；

【导师】 肖沙里；

【作者基本信息】 重庆大学 ， 光学工程， 2010， 博士

【摘要】 激光驱动X射线源的实验研究是惯性约束聚变（Inertial confinement fusion, ICF）相关物理研究的重要内容之一。激光产生高温等离子体辐射的X射线包含着十分丰富的信息,如等离子体温度、密度、离化度、不透明度以及各种输运波动和不稳定性等参数。为真实了解高温等离子体内部的状态及各种运动过程,必须通过一定的实验手段对等离子体中各种离子和电子的上述状态参数进行测量。等离子体X射线极化度作为反映等离子体内部各向异性的主要物理参数,可以辅助校验等离子体密度、温度等参量,是激光等离子体X射线极化光谱诊断的重要研究内容。极化光谱学主要研究对象是离子-电子碰撞产生的极化光谱,极化X射线对电子分布及磁场非常敏感,能够提供等离子体各向异性的信息。本论文是在国家自然科学基金项目（NSAF,No.10576041）的资助下,对激光等离子体X射线极化光谱进行较深入研究。分析等离子体X射线极化机理、诊断方法和X射线晶体衍射理论,设计了以正交布置的“双晶技术”为基础的激光等离子体X射线极化谱仪,在中国工程物理研究院激光聚变研究中心20焦耳激光装置上实验,得到了铝元素激光等离子体类氦极化光谱,验证了激光等离子体内部存在各向异性现象。重点阐述了激光等离子体X射线极化度分析模型、极化光谱诊断方法、极化晶体谱仪设计和实验过程,利用实验数据分析并计算了等离子体X射线的极化度和电子密度。论文主要内容包括:1.在国内率先开展激光等离子体极化光谱基础理论及极化度计算模型的研究。通过激光等离子体中激光与等离子体相互作用、以及离子与原子碰撞产生分裂的激发辐射分析,在磁量子数变化ΔMJ=0或ΔMJ=±1的情形下会发生塞曼跃迁并辐射极化光谱。综合分析了基于斯托克斯参量、辐射截面和布居排列辐射的三种极化度算法,这三种方法本质上具有一致性,表明极化度会随着碰撞电子能量增加而减小,并逐渐趋近于零。2.针对现有双晶法和激光装置接口问题,提出了修正双晶综合诊断方法。该方法的特点是不受光程和全偏振角限制,能够满足晶体诊断X射线的实际应用情况。其中双晶技术相对于角矢量辐射法和旋转分光计法,更适合激光等离子体极化光谱诊断。本文根据实验装置接口情况,结合等光程和全偏振角双晶法的优缺点,提出了激光等离子体极化光谱修正双晶综合诊断方法,实验表明该方法是非常有效的极化光谱诊断方法。3.根据激光等离子体极化光谱诊断方法,研制了结构新颖的激光等离子体极化晶体谱仪。传统晶体谱仪一般只有一个通道或者对称的双通道,很难满足等离子体X射线极化光谱诊断。本文采用新型的正交布置双晶结构,即在与入射电子束方向垂直的平面内正交布置两片晶体分析器,形成正交双通道。而每一个通道的晶体分析器可以灵活采用不同几何结构,如平面、椭圆及球面,其色散元件也可以采用不同的晶体材料。4.探索激光等离子体极化光谱诊断的实验方案,验证等离子体内部存在各向异性现象。基于斯托克斯参量算法,计算了等光程和不等光程两轮实验数据,获得铝离子类氦共振线w及互组合线y的极化度,分别为+0 .1204_0.0096^0.0204和+ 0.0885_0.0916^0.0679,与极化度理论值较吻合,结果显示铝激光等离子体内部存在各向异性。5.根据类氦共振线与互组合线强度比密度诊断法,结合实验光谱数据,推算出Al离子电子密度为0.9¹.5×10²⁰cm^-3,与激光等离子体电子密度理论值基本一致。通过所测极化度和密度值探讨了这两个物理参量的定性关系。实验结果数据分析表明该极化晶体谱仪的性能已满足设计要求,适合激光等离子体X射线极化光谱诊断。更多还原

【Abstract】 Experimental research of laser-produced high energy X-ray source is one of the most important parts of Inertial Confinement Fusion （ICF）.The laser-produced high- temperature plasma contains very abundant information, such as the ion temperature, electron density, ionization, opacity, transport, fluctuation, instability, etc. In order to study laser-produced plasma, it is necessary to develop a key diagnostic technology to measure the parameters of ions and electrons. Polarization spectroscopy of X-ray lines represents a diagnostic tool to ascertain the presence of electron beams in high- temperature plasmas. Polarization spectroscopy focuses on the ratio of two orthogonal components of X-ray. And polarized X-ray is susceptible to the distribution of electrons and magnetic field. The anisotropy of plasma is relevant to the temperature and density of plasma electrons.This paper was supported by National Natural Science Foundation of China under Grant No.（NSAF）10576041. It has an in-depth study in the polarization theory of laser-produced plasma.The spectrograph has been designed based on X-ray crystal diffractive principle and perpendicularly disposed double-crystal method. The first experiment was carried out at the 20J laser facility of Laser Fusion Research Center, China Academy of Engineering Physics （CAEP）. The He-like spectrum emitted from the aluminum plasma was recorded by the imaging plate, which could be used to calculate the polarizability and density of plasmas by some arithmetics.The main tasks of author were the designment and experimental studies on polarized X-ray. In this paper, we draw the following conclusions:1. In order to analyze the mechanism of polarized X-ray and the polarization degree of physical parameters in laser-produced plasma, the basic theory of laser plasma polarization and computational model of polarization were researched. The polarization effect on X-ray was discussed which including the interaction effect between laser and charged particles, the collisional excitation between electron and ion in laser-produced plasma. The Zeeman transitions and polarized X-ray occurs whenΔMJ=0 orΔMJ=±1. Three theoretical computing methods of polarized X-ray were analyzed emphatically, which are Stokes parameters, magnetic sublevel atomic kinetics, population-alignment collisional-radiative （PACR）. The simulated results of three models are essentially in agreement, which respectively based on Stokes parameters, radiation cross-section and population-alignment.It shows that polarization of X-ray will decrease and gradually approaches zero with the increase of collisional electron energy in laser-produced plasma.2. The modified comprehensive diagnosis of double-crystal was proposed,which was not restricted to equal optical length and Brewster angle and satisfied to practical application of X-ray diagnosis. Compared with the method of measuring angular emission（MAE） and rotatable spectrometer technique（RST）, the method of double- crystal is more adapt to diagnose polarized X-ray. The advantages and disadvantages of three common methods for diagnosing polarized X-ray were discussed.The method of equal optical leghth was flexible but needed two equal optical length, the method of Brewster angle normalized spectral lines based on a non-or-weak polarized line. The experiments indicate that the modified method is extraordinary effective diagnostic method of polarization spectroscopy.3. The novel polarized X-ray crystal spectrometer was developed and manufactured with perpendicularly disposed Double-crystal technique. The traditional crystal spectrometer is difficult to diagnose polarization spectrum with only one or symmetric dual channel. In this paper, the new orthogonal double-crystal structure was adopted, that is, the two crystal analyzer was orthogonal layout in the plane perpendicular to the incident electron beam direction. Single channel crystal usually can be divided into three geometric structures, which are flat, elliptical and spherical crystal with different materials.4. The experimental scheme of diagnosing polarization spectrum was explored,which could exam the properties of this spectrometer and verify anisotropic phenomenon in laser-produced plasma. By Stokes parameter algorithm, we have worked out polarization of resonance line Pw = +0 .1204_0.0096^0.0204and intercombination line Py = + 0.0885_0.0916^0.0679 followed by calculating experimental data, which are well identical to the theory. The results show the laser-produced plasma is anisotropy.5. It has experimentally diagnosed electron density of Al plasma by ratio of resonance and intercombination.The electron density of Al plasma is 0.9¹.5×10²⁰cm^-3 which is consistent with the academic value. These experimental results imply that the performance of the spectrometer satisfies the design requirements and it is a good tool for diagnosing laser-produced high-density plasma.更多还原