Control of novel power exhaust solutions in nuclear fusion
Source: https://www.tue.nl/en/news-and-events/news-overview/05-03-2026-control-of-novel-power-exhaust-solutions-in-nuclear-fusion Parent: https://www.tue.nl/en/research
Share
Control of novel power exhaust solutions in nuclear fusion
March 5, 2026
Bob Kool defended his PhD thesis at the Department of Mechanical Engineering on March 5.
Nuclear fusion is widely regarded as a promising future energy source. Yet realizing fusion power comes with major challenges such as the power exhaust problem. In the core of a nuclear fusion reactor, hydrogen gas is heated to extreme temperatures to form a plasma in which particles fuse together. This plasma is confided with a tokamak, a carefully shaped magnetic cage. Interaction with the reactor wall occurs in a dedicated exhaust region known as the divertor, but the immense heat and particle loads in this region greatly exceed material limits. In his PhD research, Bob Kool explores the control of power exhaust in alternative divertor configurations (ADCs) for the next generation of fusion reactors.
To maintain manageable conditions in the divertor, additional hydrogen and impurity gases are injected into this region. These particles interact with the plasma and dramatically reduce heat loads. However, the amount of gas required is not constant. It must be adapted in real time as the power flowing from the plasma core fluctuates. In reactor‑scale devices, such fluctuations can be fast and severe and it’s not a certainty that they can all be suppressed. This makes exhaust control an essential area of development.
Exhaust control in alternative divertors
Bob Kool investigates how ADCs affect the ability to control power exhaust. These modified divertor shapes spread the exhaust power over a larger area and improve interaction with the surrounding neutral particles to massively improve the divertor conditions. Experiments on the Mega Ampere Spherical Tokamak - Upgrade (MAST-U) in the United Kingdom were used to investigate the benefits and drawbacks of these configurations for power exhaust control systems. This research provided the first experimental insights into how ADCs respond dynamically to disturbances.
The ADCs were found to absorb fluctuations more effectively than conventional designs, which is a major benefit for exhaust control systems. Building on these insights, an exhaust controller was designed and demonstrated, achieving active exhaust control in ADCs for the first time. This confirmed that these alternative geometries can be combined with active control strategies as required for reactor-scale devices.
Limitations uncovered
The experiments also revealed important limitations. In the double‑null configuration, where an additional exhaust region is located at the upper side of the device, the distribution of power between these two divertors changes extremely quickly. Once an imbalance develops, it almost immediately affects the power arriving at each divertor target. This is likely too fast for gas actuators to counteract, making power-sharing disturbances one of the most critical challenges for reactors using this configuration.
Decoupling between the divertor and the density of the reactor
Another notable finding was the strong natural decoupling between the divertor and the density of the reactor. This effect is likely caused by the closed divertor chambers in MAST‑U and it’s a major advantage for the integration of core and divertor control systems. This decoupling was further enhanced using a Multiple-Input Multiple-Output (MIMO) control strategy, demonstrating simultaneous, near-independent control of both the upper and lower divertors together with the core plasma density for the first time.
Toward future fusion power reactors
Finally, the implications of the experimental results for reactor-scale devices were conceptually explored in the context of the Spherical Tokamak for Energy Production (STEP). The aim of STEP is to deliver fusion electricity to the UK grid in the 2040s. In addition to ADCs, this research propose predictive control elements and robust diagnostic strategies for power exhaust control. The results of this research demonstrates how alternative divertors can play a crucial role in achieving manageable exhaust conditions in fusion power reactors.
Title of PhD thesis: Power exhaust control in novel divertor solutions - Exploring real-time power exhaust control in alternative divertors with implications for the Spherical Tokamak for Energy Production (STEP). Supervisors: Dr. Matthijs van Berkel, Prof. Marco de Baar and Dr. Kevin Verhaegh.
Media Contact
Linda Milder
(Communicatiemedewerker)