Motional Stark effect (MSE) measurements of microwave-driven current profile on MAST-Upgrade (plasma strand project)

Supervisors: Roddy Vann (University of York) & Sam Gibson (UKAEA)

In the next generation of spherical fusion devices, plasmas will be predominantly heated using microwave technology. It is critical to understand on current spherical tokamaks, such as MAST Upgrade (MAST-U), how to achieve high performance plasmas heated with electron Bernstein waves (EBWs). As part of a suite of enhancements to the novel MAST-U device, high power gyrotrons are to be installed. These gyrotrons have the capability to drive up to a megawatt of injected power using EBWs. This gives us a unique and timely opportunity to investigate how EBWs modify the current and safety factor (q) profile in a fusion device for the first time.

Internal measurements of the current profile are challenging but can be obtained using novel polarimetry techniques. MAST Upgrade is a well diagnosed machine which poses an excellent opportunity to measure the current profile using the motional Stark effect (MSE) diagnostic. This diagnostic provides an essential measurement of the internal magnetic pitch angle, from which the current density distribution is inferred. Additional diagnostics such as the new synthetic aperture microwave imaging (SAMI) diagnostic can obtain current measurements at the plasma edge with high temporal resolution.

Using these two novel diagnostics, this PhD project looks to measure the impact of EBWs on the current profile, and with well assessed measurement uncertainties, validate existing current drive models. If achieved, this will allow us to exploit a vast range of new physics from the gyrotron project. Research questions to answer with this PhD project include: What is the feasibility of measuring EBW driven current using the MSE diagnostic? Can we demonstrate that EBWs can be used for q profile tailoring, and ultimately mitigate performance limiting magneto hydrodynamic (MHD) instabilities (such as tearing modes) using targeted EBW current drive?

Further development of the project could include designing a scheme for realtime control of the safety factor q profile using the MSE diagnostic. Through this project, the PhD student will become a world leading expert in q profile control using novel non-inductive current drive methods. They will develop desirable skills as a future fusion researcher such as; an innate understanding of essential plasma diagnostics, diagnostic calibration methods and measurement uncertainties. The student will become an expert in widely used fusion codes, develop their own software to analyze experimental data from a variety of optical spectroscopy, polarimetry and probe-based diagnostics. Finally, they will gain a broad knowledge of plasma physics, as well as focusing on EBW heating and current drive physics and MHD instabilities.

This project will be based at either the University of York or UKAEA depending on student preference. There will be opportunities to present research at relevant conferences and collaborate with other international fusion laboratories.

This project is offered by University of York. For further information please contact: Roddy Vann ( or Sam Gibson (

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

Figure above: Synthetic data from a newly designed imaging motional Stark effect diagnostic, modelled for a typical MAST Upgrade plasma.

Figure below: Evolution of the current profile at the edge of a MAST plasma, measured by the motional Stark effect diagnostic.