Diffusion tensor in electron transport in gases in a radio-frequency field

Electron transport theory in gases in a radio-frequency field is developed in the hydrodynamic regime from the density gradient expansion method of the Boltzmann equation. Swarm parameters for the radio-frequency (rf) field with periodic time modulation are derived as functions of both reduced effective field strength and reduced angular frequency from the time dependent velocity distribution function. The rf electron transport in phase space is analyzed from the series of governing equations by a direct numerical procedure (DNP). Electron velocity distribution function and corresponding swarm parameters obtained from DNP agree with those of the Monte Carlo simulation in the frequency range 10{endash}200 MHz at 10 Td for Reid`s inelastic ramp model gas. The temporal modulation of the ensemble average of energy and the diffusion tensor are discussed. The appearance of the anomalous time behavior of the longitudinal diffusion coefficient is discussed in particular detail, and we provide an explanation of the observed effect. {copyright} {ital 1997} {ital The American Physical Society}