【作者】 施军；

【导师】 肖沙里；

【作者基本信息】 重庆大学 ， 光学工程， 2009， 博士

【摘要】 Z箍缩喷气靶实验研究中,气体内爆产生高温等离子体辐射的X射线光谱包含着十分丰富的信息,如等离子体电子温度、密度和离化度等,这些参数通常都是依据辐射光谱强度比与谱线轮廓进行诊断。X射线极化光谱学是基于相互正交方向的X射线强度比对等离子体进行研究,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,与等离子体参数诊断紧密相关。在国家自然科学基金项目(No.10576041)的资助下,首次研制出X射线极化晶体谱仪,并在Z箍缩“阳”加速器上进行实验,探测等离子体电子温度,首次对X射线极化度进行了诊断研究。X射线极化光谱理论可以依据塞曼效应进行分析,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。X射线极化度的理论计算方法通常有光子密度矩阵法及多极辐射场法两种,其计算结果基本一致。极化度会随着碰撞电子能量的增加而减小,并逐渐趋近于零。从理论上分析X射线入射至晶体物质的反射及折射强度,推导出X射线的折射率表达式,计算出X射线的布儒斯特角约45°,检测X射线极化度的理想情形即要求X射线以布儒斯特角入射至晶体表面。晶面间距、半高宽、峰值衍射率和积分反射率是决定晶体性能的基本参数。晶面间距与被衍射X射线波长相对应,晶面间距较大的晶体既能使长波辐射发生衍射,又能使短波辐射发生衍射,但在短波段的角色散能力较低。表面处理可以改变半高宽、峰值衍射率和积分反射率。对不同类型的晶体谱仪进行分析,研制了极化晶体谱仪各部分结构:晶体分析器、闸板阀、转接法兰、胶片暗盒等,并研究了铝膜的透射率与其密度、厚度以及X射线波长之间的关系,铝膜透射率随X射线波长的增大有一定波动,而不是单调变化。极化晶体谱仪研制完成之后,在Z箍缩“阳”加速器装置上进行X射线探测实验,以诊断等离子体状态。实验成功得到理想的X射线信号,谱仪的光谱分辨率(λ/Δλ)可以达到1000以上。在此重点研究Z箍缩X射线极化度及等离子体电子温度诊断。系统地探讨了利用实验数据计算X射线极化度的三种方法,采用程序对实验结果进行处理,通过计算得到类氦共振线w及互组合线y的极化度数据。同时也分析了等离子体电子温度的三种探测方法,利用实验数据结合共振线与伴线比值测温法理论来诊断等离子体电子温度,测量结果为960~1060eV。研究极化度与Z箍缩打靶功率的关系以及极化度对等离子体电子温度诊断的影响,打靶功率高时X射线极化度会降低;而探测Z箍缩等离子体电子温度时,晶体衍射面与Z箍缩电场方向的角度变化会影响最终诊断结果,具有各向异性的等离子体都有类似特性,因此依据谱线强度比得到的等离子体电子温度、密度的诊断结果需要利用谱线极化度加以修正。更多还原

【Abstract】 In the experimental investigations of gas-puff Z-pinch implosion, the x-ray lines emitted from plasmas contain plentiful information, such as temperature, density and ionization of plasmas. Most of the spectroscopic diagnostics developed for plasmas have been based on properties of line intensity distributions and line profiles. X-ray line polarization spectroscopy is studied by changing the orientation of the crystal analyzer in separate measurements. The spectra were recorded simultaneously with two crystal crystal analyzers: one set up to record a polarization state parallel to the z-pinch column, and the other one set up to record a state of polarization perpendicular to the z-pinch axis, both crystal analyzers collected radiation emitted at 90°with respect to the z-pinch axis. Polarization x-ray lines from highly charged ions is especially useful, because such lines are typically less susceptible to the effects of magnetic and electric fields. Electron kinetic simulation and analysis of this regime indicate that the high-energy part of the electron velocity distribution exhibits noticeable deviation from a Maxwellian behavior and strong anisotropy. This paper was supported by National Natural Science Foundation of China (National Natural Science Associated Foundation) under contract No.10576041, the domestic first polarization crystal spectrograph has been successfully developed, and the experiments have been carried out at the Yang accelerator. X-ray lines emission has been used to diagnose the degree of polarization and electron temperature.X-ray line polarization spectroscopy can be interpreted with Zeeman effect. An electric dipole line transition with upper and lower states have the same value of the magnetic quantum number MJ, the emission is linearly polarized parallel to the direction of electron collision(z-axis). On the other hand, if the magnetic quantum number changes by one unit, the emission is polarized in a direction perpendicular to z-axis. The polarization degree is calculated with the multipole expansion of the radiation field and the photon density matrix in theory, and there is little different between the two approachs. The absolute value of polarization degree will decrease with the increase of collision-electron energy.The x-ray intensities of reflection and refraction from crystal are deduced in theory and the Brewster’s angle is near 45°through calculation. The Bragg angle is 45°for the optimum ratio of the crystal reflectivities of x-rays polarized perpendicular and parallel to the plane of dispersion crystal. The capability of crystal is determined by lattice spacing, full wave at half maximum, peak of diffraction efficiency and integral reflective coefficient. The lattice spacing of crystal is in connection with the wavelength of x-ray line. Crystal with high lattice spacing could diffract x-ray with long and short wavelength, but the capability of angular dispersion is feeble in short wave band. The full wave at half maximum, peak of diffraction efficiency and integral reflective coefficient can be influenced by surface treatment.Several kinds of crystal spectrographs are investigated and the frameworks of polarization crystal spectrograph including crystal analyzer, flashboard, flange and black box of film are fabricated. The x-ray transmissivity of Al has relations with its density, thickness and x-ray wavelength. It is not strictly monotone with the increasing of x-ray wavelength.The experiments have been executed to diagnose plasma at Z-pinch Yang accelerator after the polarization spectrograph is developed. The experiments suggest that the x-ray spectra emitted from Ar plasma are photographed by using the polarization spectrograph and the wavelength resolution is above 1000. In the paper the polarization degree and electron temperature of plasma are investigated. Three methods for calculating the polarization degree with spectra intensity are analyzed. The experimental results have confirmed considerable differences in the relative intensities of the Ar resonance line(w) and intercombination line(y). The linear polarization of resonance line and inter-combination line are calculated according to the intensity of the spectra. The methods for calculating electron temperature with spectra intensity are analyzed, and the electron temperature(960～1060keV) of plasma is estimated on the basis of the line ratios between dielectronic recombination satellites and the w-resonance line.We discuss of the polarization degrees and compare them with the total energy of Z-pinch. The polarization degree is decreasing with the increasing of Z-pinch energy. A characteristic feature of the spectra appears to be a distinct difference in relative intensities of the spectra registered with the two crystal analyzers simultaneously in different directions. So the polarization degree could affect on the diagnosis of electron temperature and excluding it may lead to serious overestimates of plasmas temperature. Anisotropic plasmas have the characteristics and the intensity ratios of x-ray lines have to be taken into account in plasma diagnostics for estimating plasma electron density and electron temperature correspondingly. So the further work must be done to verify all the relevant influences properly.更多还原