Alfven wave experiments in the Large Plasma Device-Upgrade at UCLA

Alfven wave experiments in the Large Plasma Device-Upgrade at UCLA will be reviewed briefly. Emphasis will be placed on an experimental observation of a stationary Alfvén (StA) wave which is a nonfluctuating, nontravelling, spatially periodic pattern in the electromagnetic field and fluid quantities [Knudsen, J. Geophys. Res. 101, 10761 (1996)]. This nonlinear Alfvenic perturbation is supported by the simultaneous presence of magnetic-field-aligned current and cross-magnetic-field plasma flow. In the upgraded Large Plasma Device (LAPD) at UCLA [Gekelman et al., Rev. Sci. Instrum. 87, 025105 (2016)], experiments were performed in helium plasma for comparison with the theoretically predicted [Finnegan et al., Nonlin. Processes Geophys., 15, 957 (2008)] patterns in ion density and electron energy. A variety of electrodes (e.g., multi-disk, mesh, emissive, etc.) provided experimental control of the azimuthal (i.e., cross-B-field) plasma flow across an off-axis positioned, along-axis-aligned, localized current channel having electron drift directed either parallel or antiparallel to the background magnetic field direction. In this talk, theoretical predictions and experimental measurements are compared for various cases. The StA wave is a plausible mechanism for the formation long-lived, static discrete auroral arcs. Observation and statistics of auroral arc formation-collapse duration (lifetime) are presented.