Tokamak transport and strong, structured flows

Fusion power is an attractive potential technology for electrical power generation. To get the next generation of fusion devices to ignite, we
need deeper theoretical understanding of the plasma turbulence which is responsible for most of the heat loss in tokamaks. In addition
to the direct practical application, understanding the dynamics of this problem is also a fascinating physics problem, because turbulence leads
of the spontaneous creation of complex structures, like blobs and shear flow layers, on scales from millimetre-size turbulent eddies
to the several-metre radius of the device itself.

One crucial aspect of turbulence is the presence of large scale flows: even in simple situations like water running over a rock in a stream,
there is a fascinating interplay between the flow and turbulent eddies downstream. Analogously, bulk plasma flows are widely recognised
as one of the key features in tokamak turbulence[12].

We outline a framework for investigating the interaction of kinetic plasma turbulence with strong flows, on the full range of length scales.
The project will extend a massively-parallel computational tool, NEMORB[6], to treat tokamaks with strong flows, and exploit this tool to study
flow self-organisation and interaction with turbulence. This requires the implementation of an advanced mathematical formalism in the code.
A key aspect is the unified treatment of flows on all length scales, in order to capture global-scale flows, flows associated with
step-like transport barriers, and turbulence-scale flow fluctuations.

This project forms part of long-term worldwide research program aimed at developing fusion power reactors. The most important impacts of this work are indirect and long term, to address the crucial problem of reliable low-carbon energy production, in order to work towards energy-independence in the UK. Outside of the university sector, this involves industrial research into magnetically confined fusion at non-government facilities.

This project will exploit research linkages between the fusion community and the broader turbulence modelling and applied mathematics community. Inter-disciplinarity is promoted at Warwick university via platforms such as the Centre for Complex System. To exploit insight developed into the grand challenge topic of far-from-equilibrium systems, a route is provided through McMillan's involvement in Bogdan Hnat's grand challenge Network-plus.

High-level interfaces between public bodies and the CFSA already exist, through the placement of senior staff members, and in particular, Richard Dendy, on government panels. This provides a route to policy impact for any relevant research outcomes.
One key stakeholder in the UK is the industrial partner at the Culham Centre for Fusion Energy UK, with whom the Proposer, and the host institution, have an established partnership. This research is of particular interest for the researchers of the MAST spherical tokamaks, where the impacts of strong rotation are known to be substantial. The ultimate outcome of the work is a dynamical model for flow organisation, which could be directly applied to make predictions in the MAST tokamak: this would be a natural fit given that Several academics at CCFE use an existing global gyrokinetic simulation code (NEMORB, which the Proposal aims to extend), and desire to exploit the proposed code extensions to make predictions at MAST as soon as they are available. The current codebase is is a production research tool for a number of institutes worldwide, including the Max-Planck Institut fur Plasmaphysik in Garching, Germany, and the CRPP at the EPFL, Switzerland.

The PDRA and graduate students involved in the project will receive training in the application of numerical techniques, and the use of high performance computing. This will serve to broaden the UK skill base in these critical knowledge areas. Warwick university also supports staff personal development through several programs incluing the transferable skills award.