The latest issue of Philosophical Transactions A looks at dissipation and heating in solar wind turbulence. Dr Khurom Kiyani, a research associate at the Laboratoire de Physique des Plasmas at Ecole Polytechnique, who guest edited the issue along with Dr Kareem Osman and Professor Sandra Chapman, talks to us about the issue as well as his own research.
Tell us a bit about what your theme issue covers.
The issue covers the latest research, and summarises our current understanding of small-scale plasma turbulence. In particular, it looks at how turbulent energy is irreversibly dissipated in a plasma without the normal channels of viscosity and electrical resistivity. It also looks at how entropy can increase in the absence of significant collisions, thereby causing the plasma to reach thermal equilibrium. Plasma physics is an incredibly rich discipline. Investigating, and ultimately understanding and solving the above problems, involves the interaction and cross-fertilisation of various fields, from statistical physics and fluid dynamics to signal processing and high performance computing. This issue attempts to cover these broad specialisations and provide the reader with an over-arching understanding of the current state-of-the-art in the topic.
What are the big challenges still remaining in this field?
The issue focuses on the unique environment of the interplanetary solar wind. Aside from obtaining an understanding of how energy is dissipated in a highly turbulent plasma, the big challenge is discerning the mechanisms behind this dissipation. There are likely to be many of these, including wave–particle interactions, plasma instabilities, and the exotic process of magnetic reconnection. Discerning such processes is crucial to solving outstanding challenges such as the coronal heating problem and how the solar wind is accelerated and heated.
The image on the front cover is particularly striking – could you explain what it illustrates?
The image attempts to illustrate both the source of solar wind turbulence – our closest star the Sun – and the complicated patterns and structures which result in turbulent plasma flows. The foreground is an actual high-resolution image of a solar prominence being emitted from the Sun’s surface, which was imaged by the Solar Dynamics Observatory. The background image shows the intensity of the current density from a snapshot of a very large resolution magnetohydrodynamics fluid simulation. This illustrates in a very striking fashion the complicated, structures which constitute the plasma flow, which are both coherent and random at the same time. In particular through this image we attempted to convey the strong roles that both observations and computational simulations/experiments have in shaping the topic. These are after all our lenses into this most complicated of dynamical systems, in which pure analytical work has consistently, and in many cases rapidly, come to un-scalable obstacles. Through the instruments on-board interplanetary spacecraft missions, and simulations which push our current computational power to its limits, we are now overcoming these obstacles and seeing glimmers of solutions.
What are you working on in your current research?
The main focus of my research is working on these problems above. Although I dabble with simulations, the main thrust of my research is observational. This involves the analysis of very large data sets from multiple instruments and multiple spacecraft — data sets which span over two decades — and developing the statistical and signal processing tools to calibrate and analyse such datasets. I am deeply fascinated with and have developed a profound respect for sound statistical methodology and the correct application of such methodology in my research. As an aside I also work on other statistically based collective dynamics such as socio-economic systems e.g. the collective dynamics of densely populated human crowds, and large scale statistical laws arising in the global financial markets.
What do you enjoy doing in your spare time?
Reading in cafes, taking long walks with my friends and spending as much time as possible with my baby daughter, Sidra. I am lucky in the sense that my work is also my hobby, so although I don’t like to admit it, I often spend a large amount of my spare time reading around my subject. In particular I really enjoy learning and tinkering with novel techniques and advancements in computational and statistical data analysis. My ideal holiday oscillates between one in which I also spend a significant amount of time learning about something completely new, or hiking a long distance over a few days.