Complexity and Plasma Physics for Fusion Power
Supervisor: Colm Connaughton (Warwick Mathematics Institute and Centre for Complexity
Science)
Co-supervisors: Richard Dendy (Warwick Physics Department and Euratom/UK Atomic Energy
Authority) and Sandra Chapman (Warwick Physics Department)
Background
The fourth state of matter, plasma, dominates the visible universe. In magnetically confined
fusion experiments such as MAST and JET at Culham in Oxfordshire, in the near-Earth space
environment, and in the solar corona, plasmas are typically characterized by extremely high
temperatures and low density. It is therefore paradoxical that such plasmas are a classic locus for
complex systems science: for an accessible outline, see “Fusion, space and solar plasmas as
complex systems” by Dendy, Chapman and Paczuski, Plasma Physics and Controlled Fusion 49
A95 (2007).
Fundamentally, plasmas support complex systems phenomenology because distinct physical
processes, operating across an exceptionally broad range of lengthscales and timescales, couple
together to deliver the observed global behaviour. In fusion experiments, for example, the overall
performance of the plasma – its ability to confine energy and burn hydrogen isotopes in nuclear
fusion reactions – is an emergent property arising from multiple coupled nonlinear processes
spanning many scales: nanoseconds to seconds, millimeters to metres.
Although there are many aspects of fusion plasmas which can be thought of under the umbrella of
complex systems, the suggested research topic for this mini-project will be ``Self organized
criticality and the sandpile paradigm''. Brief accessible papers include: “A simple avalanche
model as an analogue for magnetospheric activity” by Chapman, Watkins, Dendy et al,
Geophysical Research Letters 25 2397 (1998); “Sandpile model with tokamak-like enhanced
confinement phenomenology by Chapman, Dendy and Hnat, Physical Review Letters 86 2814
(2001); and “Solar flares as cascades of reconnecting magnetic” loops by Hughes, Paczuski,
Dendy et al, Physical Review Letters 90 131101 (2003). One possible mini-project would be to
investigate the extent to which the sandpile phenomenology developed in these papers is
applicable to a continuous driven dissipative system such a turbulent cascade which is generated
by a partial differential equation rather than a cellular automaton.
PhD Extension
The central, and most rewarding, question is to understand the how the global phenomenology of
plasmas emerges from the processes that operate on smaller spatiotemporal scales. This requires a
breadth and depth of understanding of both complex systems science and plasma physics that can
only be acquired on the scale of a PhD project. The ability to quantify, by various state-of-art
methods, correlation in strongly nonlinear experimental plasma datasets is an essential skill to
develop, and the available mini projects focus on this. CFSA is fortunate in having access to
datasets from some of the world’s leading fusion experiments, notably those at CCFE. In
addition, bearing in mind that the search for universality in plasma phenomenology is highly
topical, CFSA also has observational datasets from space-based instruments that measure cognate
natural systems.
Importantly, these datasets are available as a result of carefully developed long-term collaborative
partnerships between Warwick and large, typically international, scientific facilities. They reflect
a substantial collective investment – scientific and financial. For this reason, applications for
these mini projects are sought only from those who consider it likely that they would wish to
pursue a PhD in this area. Any follow up PhD project would be supervised by Chapman and
Dendy.