The Impact of Plasma Inflows on Magnetic Twists Along Prominence Threads

Abstract

This thesis aims to investigate the impact of plasma flows on magnetic structures in the solar atmosphere. Previous works have suggested that a coupling between plasma flows and waves in the magnetic field may amplify torsional motions in both in the presence of negative flow gradients, which prompts the need for this study. Such amplification merited investigation, particularly in the context of solar prominence formation which depend on a twisted local topology and so this could have represented an in-situ formation mechanism. The conclusions of this study express a robust analysis of twist formation in prominences, and aims to yield insights in to how and where magnetic twisting may occur from the presence of plasma flows. A short introductory review of literature and concepts is followed by three peer reviewed studies. The first of these studies investigated whether the amplification of small scale perturbations in the presence of a plasma inflow was a fundamental feature of plasma physics. Analytical solutions are constructed in terms of the generalised hypergeometric functions, and solutions are demonstrated to grow in time, despite the absence of any influxes of energy or magnetic fields. These results are confirmed numerically and an additional amplification form is discussed in the presence of fast plasma flows. The second study presented here aims to bridge the first study and the final work. A
key step in this process was understanding how magnetic threads may expand in a non-uniform magnetic field. A general divergence-free condition in curvilinear coordinates is derived and used to obtain the correct condition for the variation of a nearly vertical magnetic field. Finally the set of magnetohydrodynamic equations in curvilinear coordinates for axisymmetric motions is derived. For the final study, we model a stratified solar atmosphere, and simulate a mass loading prominence thread. The spatial and temporal evolution of torsional perturbations, driven by simulated photospheric turbulence, serves to model the arches and threads of varying lengths. We demonstrate that twist amplification is universal, however the dominant amplification mechanism varies with the length and corresponding height of the magnetic threads. Additionally, the susceptibility to twisting also varies. This study presents a broad view of how different magnetic features of the solar atmosphere may be experiencing twists and stresses.

Date of Award	2022
Original language	English
Awarding Institution	Aberystwyth University
Sponsors	Science and Technology Facilities Council
Supervisor	Yeghiazar Taroyan (Supervisor)