AlK壳层等离子体辐射谱模型的比对

Comparisons and analyses of the aluminum K-shell spectroscopic models

碰撞辐射模型的比对研究对校验发展等离子体辐射谱模型、提高等离子体参数的诊断精度具有重要意义.基于Al等离子体,对常用的辐射模型代码FAC和FLYCHK K壳层辐射谱模型开展了比对研究,详细比较了它们的离子丰度、特征线强度、谱发射率曲线和吸收系数曲线等特征,并根据各能态的速率方程,从FAC和FLYCHK模型的结构特点出发,分析了造成这些差异的原因.FAC和FLYCHK计算得到的类H、类He离子n=2,n=3激发态数密度有显著差异,进而引起特征线发射率及其比值(He-IC/He-α,He-β/H-β)的差异,从而对等离子体参数的诊断结果产生影响.除了模型中采用的能级结构和碰撞辐射过程速率外,计算结果显著地受到FAC和FLYCHK模型结构的影响.n=2激发态数密度的差异是由FAC和FLYCHK分别采用能级和超组态(组态)的方式构建n=2激发态的速率方程而引起的,而FAC代码忽略了n=3与更高激发态之间的碰撞耦合过程,是引起n=3激发态数密度差异的原因.主要特征线的吸收系数与基态能级的数密度相关,受到激发态数密度的影响较小,因此与谱发射率曲线相比,FAC和FLYCHK计算结果的差异更小.

Comparing different collisional-radiative models is of great importance for validating the models for plasma spectroscopy and improving the diagnostic accuracy of plasma parameters.In this paper,the widely applied K-shell spectroscopic models,FAC and FLYCHK,are compared based on their calculation results of the aluminum K-shell emissivity and absorption coefficient.The state abundances,K-shell line ratios,K-shell emissivities and absorption coefficients in a wide range of plasma temperatures and densities are calculated and compared,and the reasons for the differences between these two models are discussed.In an electron temperature range from 200 to 800 eV,and an electron density range from 10^（17） to 10^（24） cm^（-3）,the Al ions in the plasma are mainly composed of H-like and He-like ions.The groundstate populations of the H-like and He-like ions,calculated from FAC model,are in good agreement with the results from FLYCHK.Number densities of the excited states are two orders or more less than those of the ground states from both the models,and significant differences are observed in the number densities of n = 2 and n = 3 states of both the H-like and He-like ions.These differences will further result in the differences in spectral line emissivity and their line emissivity ratio,such as He-IC/He-a and H-β/He-β,which are key parameters used to diagnose the electron temperature and density.The line emissivity ratio Ly-α/（He-α ＋He-IC） is less dependent on the electron density,and the difference in line emissivity ratio between the two models mainly lies in the parameter region where both the electron temperature and density are high.The ratio He-IC/He-a is less dependent on the electron temperature when the electron density is more than 10^（19） cm^（-3） while significant differences are observed at a lower electron density.The reason for the difference between the number densities of the low-energy excited states from FAC and FLYCHK models is analyzed by comparing the rate coefficients of various collisional and radiative processes in the rate equation of each state.The differences in the n = 2 excited states of H-like ions come from the fact that FAC and FLYCHK models use the detailed-level model and the super-configuration model respectively to construct the rate equations of these states.The FAC model ignores the collisional excitation and de-excitation processes between the n = 3 state and higher excitation states（e.g.n = 4） in H-like and He-like ions,which are responsible for the density difference in the n = 3 excited state.Higher Rydberg states considered in FLYCHK model do not have any significant influence on the density of the ground-states.The difference in the absorption coefficient between the two models is smaller than that in the emissivity as discussed above,for the absorption coefficient mainly depends on the number density of the ions in ground state.