Power exhaust is one of the key challenges in nuclear fusion development. In his PhD research, Bob Kool explored the control of power exhaust in novel power exhaust solutions. His work showed that, in addition to improving power exhaust performance, these solutions also bring major advantages for power exhaust control. They might therefore play a crucial role in maintaining feasible exhaust conditions in future nuclear fusion power reactors. On 5 March 2026, Kool successfully defended his thesis.
The work of Kool demonstrates power exhaust control in alternative divertors for the first time. Kool conducted experiments on UKAEA’s Mega Ampere Spherical Tokamak - Upgrade (MAST-U) in the United Kingdom, where he investigated the benefits and drawbacks of these configurations for power exhaust control systems. His research can be considered as the first study that clearly shows their implications for control technology.
Super-X
Kool studied how to control heat exhaust in ‘alternative divertor configurations’ (ADCs). He specifically looked at the so called ‘Super-X configuration’ which are innovative magnetic designs that spread heat over a larger area. Kool: “MAST-U is one of the first machines built for researching alternative exhausts.”
The experiments on the MAST-U fusion device showed that these geometries not only improve the ability to handle extreme heat, but also reduce the demands on the exhaust control systems that are required in future power producing reactors. “Before we started, no one had ever shown exhaust control in alternative divertors. We have shown that it can be done, we have that confirmation now.”
First insights
Kool’s work delivered the first experimental insights into how these alternative divertors respond to disturbances. The Super-X was found to naturally absorb power fluctuations more effectively than conventional divertors, greatly reducing the response time requirements on exhaust control systems. He also demonstrated the first active control system in combination with alternative divertors. At the same time, the research identified challenges for exhaust control in the so-called double-null configuration, finding an extremely fast exhaust response to changes in how power is shared between upper and lower divertors.
The study further revealed that isolating the exhaust region physically greatly helps to decouple them from each other and the core plasma density, simplifying integrated plasma control. His findings provide valuable guidance for the first fusion plants such as the UK’s STEP program. This work highlights how alternative divertors, together with predictive control and robust diagnostic strategies, could be key to maintain acceptable exhaust conditions in fusion power-reactors.
Team performances
Going to MAST-U in the UK, was something Kool enjoyed most of his PhD trajectory: “First of all, because you get to work with the machine itself. Secondly, because I really felt like part of the team. You could say that we are important partners in science for each other, there is a lot of contact between DIFFER and UKAEA. The collaboration has grown substantially over the past years. While I was alone in the beginning, nowadays a handful of DIFFER colleagues is working together with the MAST-U and STEP team.”
In recent years, besides the many visits to the UK Kool has travelled abroad for all kinds of conferences. One of his most memorable trips was the one to Oakridge, Tennessee: “We travelled to the USA with several colleagues from DIFFER and extended our stay with a nice road trip. As expected, we had lots of fun.” What Kool and his colleagues achieved together was real teamwork, Kool says: “The weeks of working abroad were always very intense, but it's great how we did this together, as a group. For me it feels like a kind of friendship has developed in the past years.”
More to discover
- Read more about Bob Kool’s work and download the full thesis on the TU/e website (open access as of 6 September 2026)
- Article Innovation News Network (October 2025): ‘Advanced control strategies for divertor power sharing and core density regulation in fusion energy devices’
- Publication Nature Energy (September 2025): ‘Demonstration of Super-X divertor exhaust control for transient heat load management in compact fusion reactors’
- News article DIFFER (September 2025): ‘Novel ‘Super-X’ design shows major advantages in handling hot exhaust of fusion energy’
- Scientias.nl (September 2025): ‘Nederlandse onderzoekers brengen kernfusie stapje dichterbij met techniek die hitteprobleem kan oplossen’
Authors: Bob Kool, Rianne van Hoek
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