Standard Moment Method in the Problems on Ion Kinetics in Neutral Gas

ABSTRACT

A new method for calculating matrix elements of the collision integral is presented. This method is applied both for the determination of ion mobility on atom background and the construction of the ion distribution function in the case when an electric field or crossed electric and magnetic fields are switched on instantaneously. The limits of the nonstationary moment method are explored. Five interaction models are studied in detail, and the evolution of the distribution function is presented for various electric field strengths. It is shown that the angle and energy dependence of the crosssection strongly influences the distribution especially in the high velocity domain. In particular, the runaway of ions for the Coulomb interaction is determined. Moreover, the mobility vector is shown to move along a spiral to its stationary value when an electric and cross magnetic field are switched on.

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