离子分布函数的20矩近似在非相干散射谱中的应用

根据Grad理论，以麦克斯韦分布函数为基，将离子分布函数展成20矩近似的形式,讨论了黏滞张量项与热流项对离子分布函数的影响.在电场比较弱的情况下，沿着E×B和E的方向上，热流矢量项和黏滞张量项是可以分别忽略掉的.离子温度的各向异性特征和分布函数的不对称性是由黏滞项和热流项引起的.利用Sheffield理论计算得到了非相干散射谱,并对13矩近似和20矩近似得到的非相干散射谱进行了对比.在电场比较弱的情况下，这两种近似基本一致，而当电场增强时，热流张量项的贡献变得很明显，温度各向异性的特征加剧.此时与13矩近似相比较，20矩近似能够更加准确地描述以温度各向异性为特性的非麦克斯韦分布等离子体.

Application of 20-moment approximation for ion velocity distribution function in calculations of incoherent scatter spectra

According to Grad′s theory, the ion velocity distribution function is expanded about a 20-moment approximation based on Maxwellian distribution. The effects of the stress tensor and the heat flow vector on the ion velocity distributions are discussed. When the electric field is weak, it is reasonable to neglect the heat flow vector and the stress tensor parallel to E×B and E, respectively. The ion temperature anisotropy and asymmetry in the distribution function are caused by the stress tensor and the heat flow term. Then according to Sheffield′s theory and the 20-moment approximation, normalized spectrum is calculated. Finally the incoherent scatter spectra calculated by the 13-moment approximation and the 20-moment approximation are compared. When the electric field is weak, the 13-moment is nearly consistent with the 20-moment approximation. 〖JP〗However it is unreasonable to neglect the heat flow tensor, and the temperature anisotropy is distinct in case of strong electric field. It is reasonable to use the 20-moment approximation to describe the non-Maxwellian plasma characterized by the temperature anisotropy.