Nature of project: theory, software
Available to students on full-time physics degree schemes or joint students.
Alfven waves are magnetic waves that are often invoked as the only candidates that can make the journey from the photosphere of the Sun to the corona without being strongly reflected or dissipated on their way. Other types of waves are expected to decay much more rapidly, since they steepen to form small length-scales.
Alfven waves are a result of the competing effects between magnetic tension and plasma inertia. Since their discovery in the 1940s Alfven waves have been studied in various contexts including the heating of laboratory plasmas and the solar atmosphere, the formation of spicules, and the acceleration of the solar wind.
The project will explore the properties of linear and nonlinear Alfven waves. Dispersion relations for linear and nonlinear, circularly polarised Alfven waves will be derived. The effect of magnetic diffusion on these waves will be investigated.
A successful project will develop beyond the above in one/some of the following directions:
The diffusion time will be estimated analytically for different wavelengths corresponding to waves in uniform media and to waves with steep gradients. The likelihood of different types of Alfven waves reaching the corona without significant loss of energy will be evaluated.
When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.
Additional scope or challenge if taken as a Year-4 project: A dispersion relation will be derived for linear Alfven waves to examine the effects of diffusion on the wave damping and the frequencies.
Please speak to Youra Taroyan (yot) if you consider doing this project.
Initial literature for students:
The project presents an excellent opportunity for those with good analytical skills. Assistance will be provided.
|milestone||to be completed by|
|Alfven waves, their properties||end of October|
|Dispersion relations for linear and nonlinear Alfven waves||Christmas|
|Analytical estimates for the diffusion times||end of February|
|Discussion of results||Easter|