Conceptual design of an internal magnetic field diagnostic for magnetic fusion confinement devices based on cosmic muons (plasma strand project).

Supervisor/s – M. Cecconello & P. Stowell (University of Durham)

Toroidal magnetic confinement is a major avenue to achieve a self-sustaining fusion burning plasma with a positive net energy balance. The attainment of the desired magnetic field equilibrium is monitored and controlled using poloidal and toroidal magnetic field coils and magnetic flux pick-up coils that are placed outside the plasma. A careful design and implementation of the magnetic field equilibrium is required to avoid plasma instabilities that reduce the plasma performance and that can result in abrupt plasma terminations that can potentially damage the reactor. In particular, the measurement of the internal structure of the magnetic field (especially of the poloidal magnetic field) and of the plasma current density distribution is crucial to insure the MHD stability of the plasma.

Internal magnetic field measurements are inherently indirect measurements: several techniques have been developed such as Motional Stark Effect (MSE) and the observation of the deflection of the orbits of injected heavy ion beam by the magnetic field. These diagnostics provide a line integrated measurement of the magnetic field and rely on the injection of fast ions in the plasma and on the presence of strong magnetic field (above 0.5 T). The injection of fast ions is obtained using the additional heating Neutral Beam Injection system or dedicated diagnostic beams. MSE and HIBP methods are thus limited by and depend on these external sources of fast ions. In addition, dedicated HIBP and diagnostic beams complicate the overall design of a fusion reactor.

The aim of this project is to explore the possibility of using cosmic muons to measure the internal magnetic field in fusion devices and to develop a proof-of-principle design. This will be achieved by modelling of the equilibrium magnetic field in MAST Upgrade, the source of cosmic muon (flux and energy spectrum), MAST Upgrade device itself and the track detectors in sufficient details for radiation transport calculations to determined the expected signal. Radiation transport calculations will be carried out using GEANT4.

Full training will be provided on the use of GEANT4 for radiation transport and ROOT for high level statistical analysis and data inversion.

This is mainly a modelling project and will be based at Durham University. Participation to international conference and workshops are foreseen.

The project will be mainly based in Durham, but there may be opportunities to travel to conferences and collaborate with industry to support the project.

P. Stowell is a director of Geoptic a University of Durham spin-out company that develops muon sensors for ground engineering investigations. The company directors have over 20 years combined experience developing muon systems for the nuclear non-proliferation and civil engineering sectors. There is scope for the student to travel to Geoptic to learn about limitations of portable muon systems and techniques to optimise sensor placement for specific target applications.

P. Stowell is also a member of the international Muographers network, and is currently involved with a project deploying prototype muon sensors at Boulby underground lab as part of the Tokyo-bay Aqua-line project through this network. Alongside presentations at fusion research related conferences there is scope for the student to present their work at the yearly Muographers conference.

This project is offered by The University of Durham. For further information please contact: john.p.stowell@durham.ac.uk

This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.