numerical modelling of accelerated charged particles by magnetic reconnection in solar flares

Abstract

In this thesis we introduce the fundamental theory leading to the occurrence of solar flares. Observations from different missions support theoretical postulates concerning the mechanism proposed for such events, ``magnetic reconnection'', where we illustrates its basic theory, and consider one of its most important consequences, ``particle acceleration''. DC electric field associated with magnetic reconnection is now widely studied as one of the primary processes of particle acceleration in solar flares. Individual particle trajectories and acceleration due to direct DC electric mechanism in solar flares are modelled here using two approaches. The first is the full particle trajectory approach by solving Lorentz equation of motion that fully describe particle's motion. To do so we wrote what we call the ``Full Code'' that solves numerically, using different methods, the Lorentz equation. The second approach, known by Guiding Centre Approximation (GCA) Theory, is widely used when particles behave adiabatically. For this approach we used an existing code called ``GCA'' to simulate particle trajectories. A full comparison is presented to show the applicability of the GCA theory and its efficiency and when it can be used. Both approaches operate on an analogous model trying to simulate magnetic reconnection leading to the formation of a current sheet where particles are primarily accelerated and gain sufficient energy allowing them to be ejected to the outer space or come back to the Sun's surface. We consider the 2-Dimensional MagnetoHydroDynamic ``MHD'' model generating data files for background fields which serve as an input for our particle trajectory codes. We extract some limitations for important parameters such as mass-to-charge ratio and grid size and perform experiments at different locations at the current sheet (at the centre, far away from the centre, and at magnetic islands) to fully discuss differences between the 2 approaches. This coupling between particle trajectory models and data on grid arising from finite difference models is studied numerically and analytically. Different numerical methods, relativistic effects, analytical configurations, particle specie and mass effects and some others are taken into account.

Date of Award	1 Aug 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Philippa Browning (Supervisor)