To harness fusion energy on Earth, the fusion research community builds experimental reactors that trap fusion fuel and heat it to over 150 million degrees Celsius. Protecting the reactor wall from this extreme heat is a major challenge. In his research, PhD researcher Gijs Derks developed models to manage the interaction of hot fuel with the wall. On 2 March 2026 he successfully defended his thesis called ‘Dynamic exhaust modeling for fusion reactors’.
Just before his promotion, Derks was still in the United Kingdom, where he participated in an experimental demonstration for simultaneous control of both the core and the two exhausts of a fusion machine. It’s the research area Derks has been focusing on in the last four years. To be more precise, Derks focused on models in view of the operation of power producing reactors in the future.
Time-dependency
To protect the target plates of a fusion reactor, the stream of hot exhaust plasma must be actively cooled down. This is achieved by injecting gases into the exhaust region to establish a gas atmosphere. However, injecting too much gas can cool the reactor core and can hamper fusion energy production. This careful balancing act can only be performed by a control algorithm that automatically adapts the gas injection. To do that, we need time-dependent models. In his PhD research, Derks developed a simple time-dependent 1D plasma exhaust model called DIV1D.
Derks: “To test whether the time-dependence in DIV1D is good enough to design a control algorithm, its behavior is compared with experimental data from a research reactor in Switzerland. The data was specifically gathered to design an exhaust controller. The comparison shows that DIV1D can align with the measurements if it is coupled to a core plasma and a neutral gas atmosphere outside the plasma. Findings in this thesis provide a step towards the knowledge base for the design of exhaust controllers in future fusion reactors; ones that should produce net energy.”
Memories
As one of the most memorable moments of his PhD trajectory, Derks mentions the experiments he conducted at MAST-U in the summer of 2023, together with fellow researchers Bob Kool and Tijs Wijkamp. “I was staying in Nijmegen because of the Vierdaagse, a big walking event in the Netherlands. We had tested everything beforehand, like the cables between the camera and control system. Bob and Tijs were in England at MAST-U, when directly, on the first day of our experiments things went wrong. There seemed to be a gas calibration error in an algorithm we had programmed. So, 4 AM in the morning, I checked the algorithm from my guest room in Nijmegen, and contacted the colleagues in the UK. After some adjustments, they were able to redo the experiments, which succeeded!”
Next steps
After finishing his PhD, Derks will continue his career at DIFFER: “I’m going to work as a postdoc researcher, in which I will spend a third of my time at EUROfusion, to work as a research topic coordinator in machine generic integrated control. This involves coordinating control-oriented fusion experiments in Europe, taking place at TCV in Switzerland, ASDEX Upgrade in Germany, MAST-U in the United Kingdom and WEST in France. My goal is to further advance model-based control there. I will encourage them to design the controllers in advance using models. This means: that we have a well-founded design before an experiment takes place, so that we can make full use of the time we have available.”
The title of Gijs Derks’s thesis is ‘Dynamic exhaust modeling for fusion reactors’. His supervisor is Matthijs van Berkel, his co-supervisors are Egbert Westerhof and Sven Wiesen.
More to discover
- Read more about Gijs Derks’s work and download the full thesis on the TU/e website
- Article Innovation News Network (October 2025): ‘Advanced control strategies for divertor power sharing and core density regulation in fusion energy devices’
- Article DIFFER (April 2024): ‘Building the cruise control of a nuclear fusion reactor’
Authors: Gijs Derks, Rianne van Hoek
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