Torsional Alfven Oscillation in the Regime of Firehose Instability as a Mechanism of Plasma Stratification in a Laboratory Experiment on Modeling a Coronal Arch

TL;DR

This study investigates torsional Alfven oscillations under firehose instability in a laboratory plasma arch, revealing how rapid growth of these oscillations causes plasma redistribution and stratification similar to coronal loops.

Contribution

It demonstrates the excitation of torsional Alfven oscillations in a laboratory setting and links their rapid growth to plasma stratification via firehose instability mechanisms.

Findings

Unstable Alfven oscillations cause plasma redistribution.

Plasma stratification occurs along the outer wall of the tube.

Oscillations are linked to firehose instability growth rates.

Abstract

The compact laboratory stand ``Solar Wind'' (Inst. Appl. Phys. of Russ. Acad. Sci.) forms an arch structure of the coronal loop type, in which the plasma pressure varies from zero to values of the order of and above the magnetic pressure. The arc discharge in each of the bases of the magnetic tube creates a plasma that is characterized by a significantly higher ion temperature along the magnetic field line than across the latter one. In the stationary state (when the ion pressure is below the threshold value for rupture of the system at the top of the loop), the plasma is found to be stratified in the form of a cylindrical layer along the outer wall of the tube or possibly two belts along the upper and lower vaults of the arch. The paper discusses the excitation of a torsional Alfven oscillation in the loop in the regime of firehose instability. In the case of rapid growth (with an increment of the order of an ion cyclotron period), the unstable Alfven oscillation essentially reallocates the particles between the central axis and the tube wall, which manifests itself in the form of the observed cylindrical layer.