Microwave current drive in prototype spherical tokamak reactors (plasma strand) project – accepting applications

Supervisors/s: Roddy Vann (University of York), Vladimir Shevchenko (Tokamak Energy), Simon Freethy (UKAEA)

Tokamaks require an electrical current in the toroidal direction (the “long way” around the doughnut) for both plasma confinement and stability. In pulsed experiments with short plasma discharges, this has traditionally been at least partly provided by transformer action from a ramped current in a solenoid in the middle of the device.

As we move towards the reactor era, it is increasingly important that this current can be produced for long periods, which means that inductive operation cannot be used. Microwave current drive is particularly attractive because the power units can be located a long way from the device, the in-vessel launchers are relatively small and the current can be  driven locally and relatively precisely inside the plasma.

Microwaves are used routinely to drive currents at a number of tokamaks worldwide. However, significant theoretical challenges remain when translating this experience to a spherical tokamak reactor, which will be operating at much higher toroidal beta (the ratio of the plasma kinetic pressure to the toroidal magnetic field pressure) than existing devices. For example:

(a) how will the microwaves traverse the density cut-off in the plasma edge?

(b) can a series of scenarios be developed to ramp up the size and energy of the plasma whilst using the same current drive system throughout?

(c) will the microwave beam become unstable through a process called parametric decay?

(d) can the very early stages of the plasma lifetime be sustained using microwaves?

(e) can microwaves be used for ion heating as well as electron heating?

This project constitutes a three-way collaboration between the University of York, Tokamak Energy (a private company based in Milton Park, Oxfordshire) and the UKAEA Culham Centre for Fusion Energy. You will undertake modelling of both existing devices and future prototype reactors to study the feasibility of microwave current drive in a range of operational scenarios. This will require the use of a number of predictive simulation tools. Whilst these are pre-existing, you may need to write additional modules if the current codes are missing any important features. You will consider parameters spaces in simulation that have not been previously explored, whilst also validating your predictive models against experimental results from the ST40 tokamak at Tokamak Energy and the MAST-U tokamak at UKAEA.

This project will be based at York for the first 9 months. Thereafter, your time will be split between Tokamak Energy and UKAEA (both in Oxfordshire). There will be opportunities for you to present work at conferences both in the UK and overseas.

The modelling tools to be used were developed at several research centres in Europe and USA. Close contacts and collaboration with original code developers and supporters will be a part of your work throughout the entire project.

This project constitutes an exciting opportunity to work across three world-leading centres of research. As well as building technical skills in high performance computing and data analysis, you will also become an effective scientific communicator to a range of stakeholder audiences.

This project is offered by University of York. For further information please contact: Roddy Vann (roddy.vann@york.ac.uk), Vladimir Shevchenko (vladimir.shevchenko@tokamakenergy.co.uk), Simon Freethy (simon.freethy@ukaea.uk)