Diffusion of electrons in time-dependent E(t) × B(t) fields

We present results of Monte Carlo simulations for the components of electron diffusion tensor in time-varying E × B fields. In particular we follow the development of anomalous behaviour due to the change of the sign of the electric field which was found for longitudinal diffusion in purely electric rf fields (K Maeda et al 1997 Phys. Rev. E 55 5901). Similar behaviour was found to be present in crossed fields for the longitudinal N D_E component and absent for one perpendicular N D_B component. It turns out that anomalous behaviour for the N D_E×B component is induced even for a relatively small magnetic field. Reid's ramp model was used for calculations but the conclusions are quite general as these effects occur for most real gases. The transient kinetic phenomena are usually not taken into account in continuum models of rf plasmas. Our results show that it is important to include such processes in modelling and to verify the electron kinetic codes for their ability to represent the transient phenomena.