Application of 20‐Moment Approximation for Ion Velocity Distribution Function in Calculations of Incoherent Scatter Spectra

Abstract

According to Grad's theory, the ion velocity distribution function is expanded to a 20‐moment approximation based on the 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 terms. Then using 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. However it is unreasonable to neglect the heat flow tensor, and the temperature anisotropic is distinct in the case of a large electric field. It this condition using the 20‐moment approximation is able to describe more accurately the non‐Maxwellian plasma characterized by the temperature anisotropy.

Progress in polar upper atmospheric physics research in China

“…The ion velocity distribution of the Maxwell molecule collision model can be obtained using the 16-moment approximation. According to Grad's theory, Xue et al [107] found that the ion velocity distribution function was expanded about a 20-moment approximation based on Maxwellian distribution. They discussed effects of the stress tensor and heat flow vector on the ion velocity distributions.…”