Constraining the properties of turbulent solar flare acceleration regions

Abstract

Solar flares are efficient particle accelerators, with a large fraction of the released magnetic energy (10%–50%) converted into energetic particles such as hard X-ray producing electrons. However, the properties and location of the region in which electrons are accelerated to energies greater than 20 keV are not well constrained, with competing theories of the acceleration mechanism. MHD plasma turbulence is one proposed mechanism responsible for electron acceleration. The imaging spectroscopy abilities of RHESSI, and now STIX onboard Solar Orbiter (SolO), have provided spatially resolved X-ray spectra of bremsstrahlung-emitting electrons accelerated during flares. Thus, hard X-ray emission has been a vital tool in determining the properties of flare-accelerated electrons. This thesis uses multi-wavelength observations alongside state-of-the-art kinetic modelling to constrain the properties of solar flare acceleration regions (i.e., spatial extent, spatial distribution of turbulence, velocity dependence, and acceleration timescale). Firstly, EUV spectral line observations are used to map turbulence across a solar flare, the results of which suggest turbulence has a much more complex temporal and spatial structure than previously assumed. Then, a kinetic turbulent acceleration and transport model is developed. Using this model, a parameter study determines a method to constrain the properties of a turbulent solar flare acceleration region using X-ray imaging and spectroscopy diagnostics. Finally, X-ray observations are compared to model outputs to constrain the acceleration region properties of three large solar flares observed by RHESSI or STIX. This comparison successfully constrained several acceleration region properties such as the spatial extent of the acceleration region. However other acceleration region properties (i.e. the spatial distribution of turbulence) remain unconstrained and improved spatially resolved X-ray imaging and spectroscopy may help to determine these properties.

Date of Award	26 Sept 2024
Original language	English
Awarding Institution	Northumbria University
Supervisor	Natasha Jeffrey (Supervisor)