The Evolution and Dynamics of Magnetized Plasma Jets in the MoCHI.LabJet Experiment

Abstract

Magnetized plasma jets are generally modeled as magnetic flux tubes filled with flowing plasma governed by magnetohydrodynamics (MHD). Recent theoretical work has outlined a more fundamental approach based on flux tubes of canonical vorticity, where canonical vorticity is defined as the circulation of a species’ canonical momentum. This approach extends the concept of magnetic flux tube evolution to include the effects of finite particle momentum and enables visualization of the topology of plasma jets in regimes beyond MHD. Under the appropriate conditions, this framework suggests how to form and drive stable, collimated plasma jets with very long aspect ratios. To explore this possibility, a triple electrode planar plasma gun (MoCHI.LabJet) has been designed to produce helical shear flows inside a driven, magnetized plasma jet. This thesis presents the motivation, foundational theory, design, and initial results from this novel pulsed power experiment. The formation of long (1.1 m), collimated, stable jets with aspect ratios ≳20:1 was observed following an improvement to the insulation between the gun electrodes. Ion Doppler spectroscopy measurements of these jets suggest the presence of strong helical flows with sufficient shear to stabilize current driven kink-instabilities. Magnetic field measurements suggest an additional mechanism for enhanced stability by indicating that the magnetic field of the jet is qualitatively similar to a Taylor double helix. Strong flows, a plasma 𝛽≈1, and the unbounded nature of jets in the MoCHI experiment; however, are inconsistent with a Taylor state, suggesting a unique and heretofore unobserved plasma state that may be best described as a generalized, non-Taylor, driven equilibrium.