Avalanche growth in Ar+SF6 mixtures

Parameters that influence the growth of an electron avalanche are drift velocity, mean and characteristic energy, ionization coefficient and in electron attaching gases, the attachment coefficient. These parameters can be calculated by solving the Boltzmann equation numerically, and by appropriate integration of the resulting electron energy distribution. In this paper the results of such calculations have been provided for mixtures of argon and sulphur hexafluoride. The computations have been carried out over a wide range of E/N (E=electric field, N=gas number density) in each gas separately. The results are compared with the published data, to establish that correct cross sections have been employed. The technique is then extended to the mixture and the swarm parameters are presented both as a function of E/N and gas mixture ratio. An interesting finding is that the swarm coefficients and the electron-neutral collision frequency do not change monotonically as the mixture proportion is increased from argon to SF₆ An abrupt decrease in collision frequency is observed with small percentage mixtures of argon in SF₆.