Experiments and simulation of the nonlinear interaction between spinning and entangled magnetized plasma pressure filaments*

Filamentary plasma structures aligned with magnetic fields are ubiquitous in various laboratory and space plasma environments. In numerous magnetic confinement devices such coherent structures called blobs or blob-filaments, are intermittently formed in the boundary layer region of the device and transported across magnetic field lines through ExB convective motion. These structures can be much more efficient at transporting particles and energy than standard diffusive processes. The magnetized plasma pressure filaments are often created in pairs or bundles, therefore filament-filament interaction is important for purposes of estimating their lifetime. The goal of this study is to understand the nonlinear saturated state of small scale (few electron skin depths) magnetized plasma pressure filaments in close proximity that undergo drift-Alfvén wave turbulence driven by their internal pressure gradients. Experiments were designed to form multiple field-aligned plasma pressure filament structures (~10m long) within a large linear magnetized plasma device; for this purpose, the upgraded Large Plasma Device at UCLA was used. The setup consists of multiple biased probe-mounted crystal cathodes that inject low energy electrons along a strong magnetic field into a pre-existing cold afterglow plasma, thus forming rotating plasma pressure filaments with a controllable variable cross-field separation. Langmuir probes inserted in the plasma measure the low frequency (~10-20 kHz) gradient-driven fluctuations. A statistical study of the fluctuations reveals amplitude distributions that are skewed, which is a signature of intermittency in the transport dynamics. For three filaments in close proximity, large amplitude temperature fluctuation bursts have been analyzed and are related to spatiotemporal structures which propagate azimuthally and radially outward from the filaments. Details on the time scales of density, temperature and vorticity mixing in the interacting filaments alongside comparisons with fluid and kinetic simulation modeling will be presented.