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 ρi and much larger than the electron Larmor radius ρe (ρe≪r p<ρi). When the shear frequency ωS (=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.

Effects of Controlled Flow-Shear on Low-Frequency Instabilities in Magnetized Plasmas

“…In the perpendicular shear case, many experimental investigations on the relation between the perpendicular flow shears and the instabilities have been performed [15][16][17][18][19][20][21], and it has been recently reported that the net ion flow shear which is determined based on both E × B drift and diamagnetic drift is important for stabilizing the drift-wave instability [22]. In such experiments, however, there exists neutral gas and collisional effects on the fluctuations may have to be considered.…”

Sheared-Flow-Driven Electrostatic Waves in Laboratory and Space Plasmas

“…The essential element of the experiment is a strong radial electric field produced in a cylindrical shell with thickness comparable to or smaller than an ion gyroradius and the perpendicular electron current that arises in this thin layer. More recent laboratory experiments on lower-hybrid waves excited in sub-gyroradius shear layer have been interpreted with the electron-ion hybrid model and have found good agreement [34,35], however in one case the mode appears as one or more relatively narrowband spectral features in the lower-hybrid range and in the other case the mode appears as a single, more broadband, spectral feature. There is a need to explore the nonlinear manifestation of the electron-ion hybrid instability and compare it the computer simulations in the literature.…”

“…Perpendicular-velocity shear can be produced by radially inhomogeneous radial electric fields that cause the ions and electrons to have a radially inhomogeneous E Â Bdrift-velocity profile. These radial electric fields have been produced using biased, radially segmented, circularelectrode segments either at the electron-injection boundary [23,[31][32][33][34][35], at the electron-termination boundary [36][37][38], or at both end boundaries [39]. The radial profile of perpendicular-velocity is characterized by the maximum derivative ðdv =drÞ max ; the displacement L v over which the derivative is a significant fraction of this maximum value, and the difference ðv E Þ max between the large and small E Â B-drift-velocity values.…”

Interrelated laboratory and space plasma experiments

“…A Q machine [ Rynn and D'Angelo , 1960] is distinguished by its unique source that contact‐ionizes alkali atoms and thermionically emits electrons. As illustrated in Figure 15, SCAMP devices typically have a large‐diameter, low‐magnetic‐field source and a small‐diameter, high‐magnetic‐field plasma [ Ellis et al , 1980; Hansen et al , 1994; Matsubara and Tanikawa , 2000]. As shown in Figure 16, space chambers have a larger diameter plasma and a smaller magnetic field strength.…”