Development of detailed plasma-atom-molecule reaction schemes for modelling divertor gas seeding – plasma strand project

Supervisor: Andrew R Gibson (University of York, lead) and Christopher Ridgers (University of York).

Magnetically confined fusion (MCF) devices are one of the major classes of current and future fusion technology. In these systems, magnetic fields are used to confine the hot plasma so that fusion can be achieved. However, because of the enormous amount of energy present in these systems, a key challenge in the design of future MCF devices relates to properly and sustainably processing heat that is ejected from the core plasma. These heat fluxes are generally directed towards the outside of the core plasma via the magnetic field configuration in the so-called “divertor” region, where they interact with the plasma facing material of the divertor “target”. The magnitude of the heat flux incident on these plasma facing materials is generally too large for currently available materials to handle on a long-term basis. Therefore, removing power from the plasma before it reaches these materials is an important strategy for long-term operation in fusion power plants.

A key mechanism by which power is dissipated from the plasma before it interacts with the target is via radiation of excited species. This can be accentuated by the addition of seed gas impurities in the form of noble gases or nitrogen into the divertor region, which can help to “detach” the hot plasma from the target. In the detached region, a plasma with much lower electron temperature than the core – in the range of several eV to several tens of eV – is formed. At these lower electron temperatures a complex “plasma chemistry” is generated. This plasma chemistry leads to the formation of a wide range of atoms, molecules, and ions in a variety of excited states, via collision processes whose rates are dependent on fundamental atomic and molecular collision physics. A quantitative understanding of this complex mixture is important in order to understand the overall power balance in the region, optimise the divertor and the use of seed gases, and finally to minimise heat fluxes to plasma facing materials and enable sustainable, long-term operation.

In this project, the student will work at the University of York to develop plasma-atom-molecule reaction schemes relevant for divertor gas seeding, taking insights and tools from the low temperature plasma modelling community. For examples, see references [1 – 3] below. The ultimate direction of the project is flexible and can be tailored to the particular interests of the student, in discussion with the supervisory team. As an example, a project outline may include some or all of the following aspects. (1) Development of a detailed reaction scheme for plasma-atom-molecule interactions occurring during divertor gas seeding. The study of nitrogen seeding, i.e. hydrogen/nitrogen mixtures, is envisaged, however, other seed gases are also possible, and the final decision on gas mixtures will be made during the project itself. These studies will be carried out using a 0-D modelling framework available in the group. (2) Development and application of model reduction methods to produce simplified reaction schemes for use in multi-dimensional simulation frameworks for the divertor, such as Hermes-3. (3) Use of Hermes-3 for multi-dimensional simulations of the physics and chemistry in the divertor region with a more detailed plasma chemistry.

Within the project the student will have the opportunity to develop valuable skills in coding, for example in Julia and Python, simulation methods and fundamental atomic and molecular physics. Students will also have the opportunity to gain skills and experience in teamwork, communication, scientific writing and scientific presentation.

Since the project topic sits at the boundary between fusion and low temperature plasma science, the student will have the opportunity to work with scientists in both research areas. This could, for example, include collaborations on model validation with other members of the low temperature plasma group at the University of York with interests in this area, such as James Dedrick and Erik Wagenaars.

National, and international collaborative opportunities will also be possible within the project, and can be tailored based on the interests of the student in consultation with the supervisory team. Presentation of work at national and international conferences is also strongly encouraged. Together, this will give the student the opportunity to develop deep scientific networks and experience of different research environments.

[1] Helen L Davies et al 2023 Plasma Sources Sci. Technol. 32 014003 https://doi.org/10.1088/1361-6595/aca9f4

[2] Gregory J Smith et al 2024 Plasma Sources Sci. Technol. 33 025002 https://doi.org/10.1088/1361-6595/ad1ece

[3] M Osca Engelbrecht et al 2024 arXiv Preprint, arXiv:2402.08092 https://doi.org/10.48550/arXiv.2402.08092

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

This project is offered by University of York. For further information please contact: Andrew R Gibson (andrew.gibson@york.ac.uk)