Sheared ExB Stirring and Cross-Field Electron Inertial Length Structuring Generated by Shear Alfvén Wave Heating

Alfvén waves play many important roles in the interaction of the Earth’s magnetosphere and ionosphere. In one significant example, shear Alfvén waves triggered by reconnection in the magnetotail carry energy along field lines mapping back to the auroral ionosphere; there, where the electron thermal speed is small compared to the Alfvén speed, electron inertial effects are important, and these Inertial Alfven Waves (IAWs) possess a parallel electric field which accelerates electrons. In some cases, the incoming IAW Poynting flux is sufficient to completely power the aurora [1]. Measurements of the electron acceleration process have even been recently performed in a laboratory plasma [2]. Bulk heating of electrons can also occur by IAWs when electron-ion Coulomb collisions become important in the lower ionosphere. The cross-field density of the ionospheric plasma has been found to contain a great deal of structure, including density cavities. Some of these cavities are co-located with IAWs and measurements by the FAST satellite [3] show that the waves can create the cavities. We present results of an investigation aimed at complementing the understanding of such phenomena from a parameter-scaled, laboratory experiment. Our results demonstrate that, among other effects, sheared cross-field ExB flows can restructure any existing plasma nonuniformities into what appear to be electron-inertial length scale wavelike features, as well as generate expanding, cross-field diffusion waves.