Laboratory investigation of boundary layer processes due to strong spatial inhomogeneity

Abstract

Laboratory experiments have been conducted to simulate the dynamics of highly localized magnetospheric boundary layers. These regions, such as the plasma sheet boundary layer and the magnetopause, are primary regions of solar wind mass, energy, and momentum transport into the near-Earth space environment. During periods of solar activity, the boundary layers can become compressed to scale lengths less than an ion gyroradius. Theoretical predictions indicate that the plasma can respond to relax these highly stressed conditions through the generation of instabilities in the lower hybrid frequency range. The experiments reported here document the characteristics of waves associated with these instabilities.

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.…”

Upgrades to the Auburn linear experiment for instability studies

“…In ALEXIS and other magnetized linear plasmas, this control is often accomplished through the use of one or more concentric rings, located either at the end of the column opposite the plasma source, 27,30 or at the center of the column using electrodes with a sufficiently low enough opacity that the plasma can pass through the ring or rings. 31 ALEXIS implements the former configuration, with a set of concentric rings that can be independently biased with respect to ground.…”

Coherent structure generated in the boundary layer of a laboratory‐created ionospheric depletion

“…The onset of EIH mode leads to the formation of vortex-like coherent structure in the electrostatic potential [Romero et al, 1992b], which are believed to play a crucial role in the evolution of the ionospheric depletion. Such vortex-like coherent structures possibly exist in some artificially created ionospheric irregularities [Scales et al, 1994b;Fu and Scales, 2013] and laboratory-generated sheared E × B flows [Amatucci et al, 2003;DuBois, 2013;DuBois et al, 2013]. However, few laboratory experiments have been specially designed to study the formation and evolution of the coherent structure until recently.…”