Boltzmann Equation Analyses for the Relaxation of Velocity Distribution of Neutrals with the Transient FTI Method

The relaxation process of the velocity distribution of neutral atoms injected into dilute atomic gases with Maxwellian and non-Maxwellian velocity distributions has been analysed by numerically solving the Boltzmann equation using the transient FTI method. Here, only isotropic scattering in the center of mass frame and the collision characteristics of constant collision frequency and of constant collision cross section are assumed. Numerical analysis for the relaxation of the velocity distribution of the entire gas with a non-Maxwell initial distribution was also carried out by linearizing the Boltzmann equation sequentially in time. The results obtained are very simple and suggestive. The mechanism driving the neutrals toward the Maxwell distribution is discussed.