Laminar and Turbulent Plasmoid Ejection in a Laboratory Parker Spiral Current Sheet

TL;DR

This study investigates the formation and ejection of plasmoids in a laboratory and simulation setting, revealing how pressure gradients influence whether plasmoids are laminar or turbulent, and providing a model consistent with solar observations.

Contribution

It introduces a heuristic model explaining plasmoid formation due to loss of equilibrium, linking laboratory, simulation, and solar streamer phenomena.

Findings

Laminar plasmoids occur at modest pressure gradients.

Turbulent plasmoid ejection happens at higher drive conditions.

The model predicts plasmoid periodicity consistent with solar observations.

Abstract

Quasi-periodic plasmoid formation at the tip of magnetic streamer structures is observed to occur in experiments on the Big Red Ball as well as in simulations of these experiments performed with the extended-MHD code, NIMROD. This plasmoid formation is found to occur on a characteristic timescale dependent on pressure gradients and magnetic curvature in both experiment and simulation. Single mode, or laminar, plasmoids exist when the pressure gradient is modest, but give way to turbulent plasmoid ejection when the system drive is higher, producing plasmoids of many sizes. However, a critical pressure gradient is also observed, below which plasmoids are never formed. A simple heuristic model of this plasmoid formation process is presented and suggested to be a consequence of a dynamic loss of equilibrium in the high-$\beta$ region of the helmet streamer. This model is capable of explaining the periodicity of plasmoids observed in the experiment and simulations and produces plasmoid periods of 90 minutes when applied to 2D models of solar streamers with a height of $3R_\odot$. This is consistent with the location and frequency at which periodic plasma blobs have been observed to form by LASCO and SECCHI instruments.