Anomalous Cross-Field Transport of Electrons Driven by the Electron-Ion Hybrid Instability Due to the Velocity Shear in a Magnetized Filamentary Plasma

Abstract

The effect of cross-field velocity shear of electrons on the plasma transport has been experimentally investigated in a steady-state filamentary plasma whose effective column radius r p is smaller than the ion Larmor radius ρ i and much larger than the electron Larmor radius ρ e (ρ e ≪ r p <ρ i ). When the shear frequency ω S (= v 0 / L E , where v 0 is the maximum flow velocity in the sheared flow and L E is the shear scale length), which is the measure of the strength of the velocity shear, becomes much larger than the lower hybrid frequency, electrostatic plasma fluctuations of the lower hybrid range of frequency are excited in the significantly sheared flow. It is observed that these enhanced fluctuations induce the anomalous, non-ambipolar diffusion of electrons across magnetic field lines. The estimated cross-field diffusion coefficient of electrons obeys the Bohm scaling. The observed instability can be identified as the electron-ion hybrid shear instability through comparison between experimental and numerically obtained results.