The swarm parameter has been calculated as a function of the amount of NF3 in Ar, He and N2 using the two-term Boltzmann equation. In particular, the attachment coefficient and attachment rate coefficient in NF3 are compared with the experimental values measured by Lakdawala et al. The large discrepancies between the measured and calculated values of the attachment rate coefficient for NF3 mixture in Ar, which were pointed out by Lakdawala et al., are discussed.

We propose a numerical method to obtain the drift velocity and the diffusion coefficient for ions moving in neutral gases using random walk theory. This method can be applied to the experimental study of ion swarms very efficiently. We verified the validity of our method with computer simulation and the analysis of the experimental result obtained by Takebe et al. [J. Chem. Phys. 73 (1980) 4071]

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Mixing time of N2 and SF6 was measured. The local mixing ratio was determined by variation of the corona onset voltage on the needle-plane electrodes. Owing to the mass difference of two kinds of gases the mixing time was influenced by mixing methods. The mass difference makes flow of the gases in the mixing container and accelerates the diffusion. Then the wide range of diffusion (or turbulent diffusion) coefficients was obtained.