Rectification effect of gradient antiparallel magnetic fields on electron conduction in a gas under a radio-frequency electric field

Electron transport in CF4 under linearly gradient antiparallel magnetic fields was analysed in order to investigate the fundamental properties of magnetic neutral loop discharge plasmas used for material processing. The electron motion was simulated by a Monte Carlo method under a radio-frequency (rf) electric field applied perpendicularly to the directions of both the magnetic field and its gradient. Two typical electron motions, meandering in a weak magnetic field and gyration in a strong magnetic field, were observed with particular directionalities. The meandering electrons drifted forward on average similarly to those under a dc electric field. The gyration induced an electron drift towards the inverse direction. The direction of electron flux was dependent not only on the rf phase but also on the distance from the magnetically neutral midplane between the antiparallel magnetic fields. The electron conduction path formed along the midplane had a structure consisting of forward and inverse lanes. A peculiar result was that the direction of local electron flux was always forward in the strong magnetic field whereas the drift of gyrating electrons was towards the inverse direction. This seemingly paradoxical result can appear in the presence of the density gradient of the electron distribution.