Drift-Alfvén fluctuations and transport in multiple interacting magnetized electron temperature filaments

Abstract

The results of a basic electron heat transport experiment using multiple localized heat sources in close proximity and embedded in a large magnetized plasma are presented. The set-up consists of three biased probe-mounted crystal cathodes, arranged in a triangular spatial pattern, that inject low energy electrons along a strong magnetic field into a pre-existing, cold afterglow plasma, forming electron temperature filaments. When the three sources are activated and placed within a few collisionless electron skin depths of each other, a non-azimuthally symmetric wave pattern emerges due to interference of the drift-Alfvén modes that form on each filament’s temperature gradient. Enhanced cross-field transport from chaotic ( $\boldsymbol{E}\times \boldsymbol{B}$ , where $\boldsymbol{E}$ is the electric field and $\boldsymbol{B}$ the magnetic field) mixing rapidly relaxes the gradients in the inner triangular region of the filaments and leads to growth of a global nonlinear drift-Alfvén mode that is driven by the thermal gradient in the outer region of the triangle. Azimuthal flow shear arising from the emissive cathode sources modifies the linear eigenmode stability and convective pattern. A steady-current model with emissive sheath boundary predicts the plasma potential and shear flow contribution from the sources.

Emissive cathode immersed in a plasma: plasma–cathode interactions, operation and stability

“…For instance, the Big Red Ball [35] and the Plasma Couette eXperiment [36] at the University of Wisconsin implement the interaction of large current injection from emissive cathodes with large-scale or multipolar magnetic fields to study laboratory astrophysical relevant phenomena such as the dynamo instability, the magnetorotational instability or the dynamic of the Parker spiral in the solar wind [37]. Hot emissive cathodes immersed in a preexisting plasma also shed new light on transport and plasma turbulence in magnetized plasma columns [38,39], plasma flow generation [40,41], or the dynamic of interacting plasma filaments [42,43]. The control of electric fields perpendicular to the ambient magnetic field is also crucial for a number of applications of E × B configurations [44], and among them, high-throughput plasma mass separation [45,46].…”