We research plasma processes in the Sun and beyond, developing mathematical models of the complex interactions between plasmas and magnetic fields.
Some key research questions are:
• How is plasma in the solar corona heated to temperatures of millions of degrees?
• How does the process of magnetic reconnection work in the solar corona and elsewhere?
• What is the origin of high-energy charged particles in solar flares?
We are also involved in modelling the interaction of plasma with magnetic fields in magnetically-confined fusion devices such as spherical tokamaks.
A central theme of our research is modelling the nature and effects of magnetic reconnection in the solar atmosphere. Magnetic reconnection is a process of fundamental importance in astrophysics, with relevance ranging from galactic magnetic fields, to stellar and solar activity, to planetary magnetospheres, as well as in magnetically-confined fusion plasmas. Reconnection restructures magnetic fields and provides an efficient means for converting magnetic energy into thermal energy and particle kinetic energy – thus, it plays a central role in solar flares and coronal heating.
Our knowledge and understanding of the solar atmosphere has been revolutionised in recent decades by a wealth of observations, especially from space observatories such as (currently) Solar Dynamic Observatory, RHESSI, IRIS and Hinode. However, new observations have increasingly revealed the complex and dynamic nature of solar magnetic activity, and significant advances in theory and modelling are required in order to understand the physical processes. A particular challenge for theory is the vast range of spatial scales – from global scales of the order of Mm, which can be well treated using a fluid approach, down to plasma scales, such as the ion gyro-radius, of the order of m or less, which require kinetic models. Our research thus utilises both magnetohydrodynamic (fluid) models and kinetic plasma approaches, and we are currently developing new techniques to bridge the gap between fluid and kinetic scales. Our modelling involves both large-scale numerical simulations and analytical calculations.
Solar flares are dramatic and complex events which are of interest both in their own right and because of their significant effects on the Earth's space environment by shaping "space weather". A solar flare involves the release of up to 1025 Joules of stored magnetic energy, in timescales of minutes - hours, with signatures across the electromagnetic spectrum. There is now a considerable body of evidence demonstrating that magnetic reconnection is the fundamental process of energy release in solar flares. However, many mysteries remain unsolved. One challenge is to explain the origin of the large numbers of high-energy charged particles which are observed, and we are developing models to tackle this question.
Explaining how solar coronal plasma maintained at temperatures of millions of degrees Kelvin, while the surface temperature is only a few thousand degrees, is a major unsolved problem in astrophysics. A promising candidate for effective dissipation of stored magnetic energy is magnetic reconnection, the same process which is responsible for the energy release in large-scale solar flares. It has thus been proposed that coronal heating is due to the combined effect of many small flares, known as nanoflares. We are currently involved in modelling heating by nanoflares, focusing on energy dissipation in twisted magnetic fields.
Over recent years, we have pioneered models of heating in twisted magnetic flux ropes triggered by the ideal kink instability, with application both to understanding confined flares and to coronal heating. Recent work has focused on predicting the observational signatures of heating in twisted fields, considering both thermal (EUV) and non-thermal emission (Hard X-rays, microwaves).
Our research is supported by grants from STFC. We have active collaborations with groups in the UK and internationally.