When Can Swarm Data Be Used to Model Gas Discharges

Abstract

Electron swarm data (e.g., first Townsend coefficient, diffusion coefficient, drift velocity) have at least two important uses. The first is that swarm data may be used to derive electron impact cross sections. These cross sections may then be used, in conjunction with solving Boltzmann’s equation, to obtain reaction rate coefficients to model gas discharges. The second use is to directly model gas discharges using the coefficients obtained from swarm experiments. The use of swarm data in this manner presupposes that the conditions under which the swarm parameters were measured resemble those of the gas discharges in question. With this in mind, one must consider whether differences in current density, nonequilibrium aspects of the electron energy distribution, and cleanliness of the system affect the validity of using swarm data to directly model gas discharges in this manner. In this paper, we discuss the parameter space in which swarm data may be directly used to model gas discharges, while paying attention to these parameters. We will also suggest that swarm data may be extended beyond the accepted parameter space by using scaling laws.