Evolution of an arched magnetized laboratory plasma in a sheared magnetic field

Kamil D Sklodowski,Shreekrishna Tripathi,Troy Carter

doi:10.1017/s0022377821001239

Kamil D Sklodowski, Shreekrishna Tripathi + Show 1 more

Open Access

https://doi.org/10.1017/s0022377821001239

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Abstract

Arched magnetized structures are a common occurrence in space and laboratory plasmas. Results from a laboratory experiment on spatio-temporal evolution of an arched magnetized plasma ( $\beta \approx 10^{-3}$ , Lundquist number $\approx 10^{4}$ , plasma radius/ion gyroradius $\approx 20$ ) in a sheared magnetic configuration are presented. The experiment is designed to model conditions relevant to the formation and destabilization of similar structures in the solar atmosphere. The magnitude of a nearly horizontal overlying magnetic field was varied to study its effects on the writhe and twist of the arched plasma. In addition, the direction of the guiding magnetic field along the arch was varied to investigate its role in the formation of either forward- or reverse-S shaped plasma structures. The electrical current in the arched plasma was well below the current required to make it kink unstable. A significant increase in the writhe of the arched plasma was observed with larger magnitudes of overlying magnetic field. A forward-S shaped arched plasma was observed for a guiding magnetic field oriented nearly antiparallel to the initial arched plasma current, while the parallel orientation yielded the reverse-S shaped arched plasma.

Highlights

Arched magnetized plasma structures are ubiquitous in the solar atmosphere
The reversal of the sign of the sigmoid with a guiding magnetic field is confirmed. These results indicate that the arched plasma is not in a force-free state
The effect of a nearly horizontal overlying magnetic field on the evolution of an arched magnetized plasma has been studied in this laboratory plasma experiment

Summary

Introduction

Arched magnetized plasma structures are ubiquitous in the solar atmosphere. Solar prominences and coronal loops are notable examples of such structures that confine a current carrying plasma by closed magnetic fields. Modelling solar prominences in a laboratory or computer simulation often involves creation of flux ropes – twisted magnetic structures arising from a significant poloidal magnetic field generated by a toroidal electrical current (see figure 1(b) for coordinates) (Low 2001; Fan 2005; Chen 2011; Török et al 2011). The generation of laboratory experiments on arched plasmas were developed in the early 2000s by the Caltech group (Bellan & Hansen 1998; Hansen 2001; Hansen, Tripathi & Bellan 2004; Tripathi, Bellan & Yun 2007) Their findings included an explanation of sigmoidal shapes and filamentation of the current channels via a force-free state equation, and demonstration that the strapping field can inhibit the eruption of solar prominences. The parallel and antiparallel orientations of the guiding magnetic field have been correlated with the occurrence of forward-S and reverse-S shaped arched plasmas

Experimental set-up

Results and discussion

Summary