Astrophysics PhD Projects 2011

Note that these are suggested project topics rather than projects for which a funded PhD place is necessarily available and will evolve over time. Please contact the supervisor concerned for details.

You can consult the list of project topics in plasma physics by opening this PDF file.

Other joint astrophysics projects are also available with the Institute for Gravitational Research, mostly on the analysis of recent gravitational wave data: contact Prof G. Woan for details.

Neutron astronomy

Supervisor: Dr A. MacKinnon

Free neutrons in space testify to the bombardment of some baryonic target (Sun, planets) by energetic ions. They are a crucial diagnostic of transient solar ion acceleration (in flares, but possibly also at other times). They will also result from other cosmic targets bombarded by cosmic rays. The main focus of this project will be the development of data analysis techniques for innovative neutron detectors, being developed by our collaborators in the University of New Hampshire (UNH) with a view to flying on future inner heliosphere space missions. A major side theme will be the modelling of nuclear processes that produce free neutrons, to explore fully their diagnostic potential. The project will involve working closely with collaborators in UNH and elsewhere.

Pulsar Magnetospheres

Supervisor: Dr D. Diver, Dr H. Potts

Pulsar atmospheres consist of electron-positron plasmas. Such plasmas are very energetic, and given that the positive and negative species have equal mass, these plasmas have unique properties. We are investigating wave propagation in magnetised pair plasmas, from the perspective of trying to understand the wave processes that could contribute to the pulsar radiation source. To date we have examined the radiation damping of quasi-linear electron-positron plasma oscillations, using computer simulations. Complex analysis has allowed us also to reformulate the Bernstein modes in a weakly relativistic pair plasma, with a view to studying how such weakly damped magnetic modes might act as a vehicle for radiation transport in a non-uniform plasma. The landau damping of fully relativistic pair plasmas is also a developing investigation.

The project will be concerned with

1. developing simulations of the interaction between fast particle streams and large-amplitude collective oscillations;
2. extending our analytical attack on realtivistic Landau damping, and exploiting the new physics that arises; and
3. creating the necessary relativistic transformations that allow the radiation field to be translated into the observer's frame.

Plasma Sheath stability and plasma acoustics

Supervisor: Dr D. Diver, Dr H. Potts

A project to model (i) the impact that a plasma source can have on neutral gas and (2) the time evolution of the sheath around a free-surface in a streaming plasma.

1. In plasma acoustics, the ion wind and localised heating of a plasma source in a neutral gas can trigger significant sonic disturbances
2. In the sheath stability studies, the electrostatic environment at the perimeter of a possibly deformable conducting (or dielectric) structure placed directly in a flowing plasma.

These projects are computational and analytical in character, sharing basic plasma physics but applied to different situations. Several competing scale-lengths will contribute to the complexity of the evolution: the collisional mean free path of the plasma, the free-fall sheath length scale, the typical wavelength of deformation of the conductor and the scale-length for non-uniformity of the plasma flow. The competition between these characteristic scales will lead to strong time-dependence in the local electric field, and the consequence non-linear feedback on both the impinging plasma flow, sonic disturbances and the free-surface deformation of the obstruction. The most obvious application of the sheath stabilitiy analysis is to space tethers in the solar wind environment, but the relevance extends beyond this to spacecraft generally, and to laboratory plasmas used for surface processing in which the surface topography evolves self-consistently. Analysis of photoionisation of the lunar regolith, and the consequent development of the lunar plasma exosphere, is another possible research project. For the plasma acoustics, the direct generation of sound waves by plasma heating has a long history, but recent advances in plasma technology mean that this exciting problem can be tackled afresh. Our particular interest is in the generation of pressure disturbances orders of magnitude greater than normal acoustics, but in specialised vessels that suppress shock formation.

Self-consistent dust growth in plasmas

Supervisor: Dr D. Diver, Dr H. Potts

The evolution and character of plasma dust has wide-ranging implications for astrophysics and laboratory plasmas, including fusion and plasma processing. Whilst there are many studies of plasma crystals, in which pre-formed grains are injected into a plasma, there are fewer investigations of the more profound problem of growing the dust from first principles directly in the plasma.  Condensation mechanisms, in which fluid agglomerates around a seed particle in the classical Salpeter approach, are not as relevant in the plasma context, since in the latter the local electrostatic conditions can influence enormously the conditions for dust growth, leading in some cases to naturally occurring prolate-spheroidal dust shapes. The implications of non-spherical dust grains for electromagnetic extinction and polarisation in astronomical observations are well-known, but though progress has been made in characterising the effects of composite grain structure and spheroidal  shapes, there is little in the way of a holistic approach to the problem. We aim to model the formation and evolution of dust in the original supporting plasma, and then simulate the remote diagnosis of the medium by computational analysis of the resulting polarisation signatures. We will examine the electrostatic charging of dust over a range of scales, and its subsequent growth, with and without a magnetic field. Surface chemistry, particularly the absorption of gases, will be accommodated where appropriate.

Cosmic Magnetism and Plasma Cosmology

Supervisor: Dr D. Diver, Dr L. Teodoro & Dr M. Hendry

The role of the magnetic field in medium scale cosmic evolution is not well understood, given the complexity of the possible interactions. We aim to focus on two specific areas: (1) the natural evolution of jets and other linear structures; (2) the development of density structure in large-scale mixed flows of plasma and neutrals; and (3)the evolution of magnetic fields in extreme circumstances, from the weak but large-scale cosmological magnetic field, to the intense, but highly-localised pulsar field.
(1) Self-guiding magnetic fields arising from energetic plasmas have been modelled (computationally and analytically) in the context of dense, relativistic plasma flows in laser-plasma interactions. These fields are produced by Inverse Faraday Rotation, in which the internal plasma currents create an axial magnetic field component that is projected ahead of the plasma front, so guiding the direction of the flow. Such phenomena could play a role in the evolution of large-scale astrophysical jets, in which rectilinear structures stretch for remarkably large distances with very little deviation, but with tell-tale internal structure that is suggestive of strong axial plasma rotation.
(2) Plasma-neutral gas mixtures are a unique medium, if momentum transport is incorporated between the charged fluid and its neutral counterpart. Density structures evolve that are hybrids of the plasma response to magnetic perturbations, and the neutral gas sonic pressure waves. The resulting mixture leads to an anisotropic medium that can support a large variety of pressure variations, with disturbances propagating with complex group and phase velocities. Linear computational studies already hint at beautiful structures; we plan to push on with a fully non-linear model that will allow larger perturbations to evolve.
(3) Magnetic field evolution in the early universe prior to recombination is uncertain; however, the effect of recombination must be significant, since the large-scale formation of neutrals has a major impact on the conduction current. Removing the charged particle current carriers must induce an electromagnetic response, and this project will address the relevant physics: by incorporating the correct electromagnetism and plasma kinetics, we will investigate (a) the acceleration of ambient charged particles by the creation of a displacement current, and (b) the intrinsic evolution of the distribution function during recombination, and the interpretation of the temperature during this behaviour.

Surface flow induced ionization in the Sun

Supervisor: Dr D. Diver, Dr H. Potts

A numerical and theoretical investigation of Alfven ionization processes in strong solar photospheric flows. The kinetic energy of mixed-species neutral gas flowing through a magnetised plasma can result in pockets of energetic plasma electrons (confined by the magnetic field) that are able to ionize specific neutrals in the flow via electron-impact ionization. Such  a process has already been implicated in creating the anomalous chemical composition of the solar wind; we aim to extend this study by correlating solar surface flows and magnetic structures together with improved data on solar abundances to clarify the overall picture of ionised species evolution in the magnetic environment of the sun. Specifically, this project will address the creation and transport of particular ions via interaction with a defined magnetic structure, investigating the differential diffusion of minority species in order to model directly the resulting abundance anomalies in the solar wind. This will allow us to incorporate time-dependence arising from the photospheric flows and the character of the magnetic structures, as well as longer timescales invoked by the solar cycle.

Diagnostics of particle acceleration on the Sun - a cosmic prototype

Supervisors : Prof. J. C. Brown; Dr A.L. MacKinnon; Dr. L. Fletcher

Particle acceleration is a ubiquitous cosmic phenomenon from the scale of active galactic nuclei down to planetary magnetospheres with the resulting fast particles having an energy density high enough to influence their environment. Acceleration processes are far from well understood, either theoretically or phenomenologically from data interpretation. The nearby sun offers a unique opportunity to study particle acceleration via high resolution spectra and images at radio to gamma-ray wavelengths from ground and space observatories, and by direct particle detection in space, (Solar energetic particles are a key component of Space Weather and its effects on the Earth environment.) As the UK Co-I Group on the NASA high energy RHESSI solar mission (http://hesperia.gsfc.nasa.gov/hessi/) , and with close involvement in other solar missions, Glasgow is involved in a wide range of theoretical and numerical projects on diagnosing data on solar electron and ion acceleration. Results are used as tests of particle acceleration and transport models and of the role of particles in heating of the flaring and active solar atmosphere. A range of possible thesis topics is available in these areas, all involving varying mixes of : data mining and reduction; signal analysis (spectrum and image deconvolution); tests of phenomenological models against data; numerical simulations and analytic modelling of plasma/particle processes. Work in this area involves numerous collaborations including NASA Maryland, Berkeley, Alabama, Lockheed-Martin CA, Graz, Genova, Paris and Zurich.

Particles, Plasma and Electromagnetic Waves in the Heliosphere

Supervisors: Dr E. P. Kontar; Prof. J. C. Brown; Dr. L. Fletcher

Analysis and interpretation of Hinode observations of solar flares and related phenomena

Supervisor: Dr. L. Fletcher

1. Analysis of Hinode magnetic field observations to identify the locations of photospheric field changes, and their relationship to plasma heating and particle acceleration
2. Imaging and spectroscopic studies of large-scale coronal disturbances such as propagating flare waves and flows, to understand their origin and drivers
3. Spectroscopic studies of solar flare plasmas

Data analysis is core to this project, however candidates with a strong interest in theory will be encouraged to explore theoretical modeling relevant to their observations.