In the final months of 2023, as researchers and engineers across Europe converge on the Culham Science Campus near Oxford, the Joint European Torus (JET) reactor is in the spotlight. This doughnut-shaped fusion device, Europe’s flagship experimental fusion reactor for four decades, is set to retire and enter decommissioning in the new year. But before it does, the JET team is squeezing every last bit of scientific insight from the reactor, culminating in a new world record for the most fusion energy released in a single shot. This achievement is not just about setting records; it’s about pushing the boundaries of our understanding of fusion energy and paving the way for future power plants.
Among the flurry of experiments, a team of Dutch researchers, led by PhD candidate Thomas Bosman, is focusing on managing the heat exhaust in future fusion power plants. Their task is to fine-tune a control algorithm that guarantees detachment—a regime where heat is diffused before it touches the reactor wall—in just three ten-second plasma shots. Bosman explains, “In JET, the plasmas are short and relatively benign. Sturdy wall materials like tungsten can manage the heat directly. But future fusion power plants will be an order of magnitude more powerful, with much harsher conditions. If you do not manage the heat exhaust very carefully, you could damage the inside walls in seconds.”
Bosman’s approach is a testament to the power of engineering in fusion research. While physicists have spent years understanding the underlying interactions between the outer plasma edge, the plasma core, and the reactor walls, Bosman and his colleagues have managed to fine-tune a control algorithm without delving into the complex physics. “In principle, that was all the information we needed to set the rules for our controller,” Bosman recalls. This success is a significant step forward in the engineering approach to fusion, demonstrating that even complex systems can be managed with basic models.
However, Bosman is quick to acknowledge that this success is built on years of physics research. “Getting there took years of physics research to understand the heat problem and develop a scenario to manage it; without that solid foundation, Bosman’s controller would not know where to start or what to achieve.” This interplay between physics and engineering is crucial for the future of fusion energy.
Looking ahead, the challenges in fusion control are far from over. Bosman acknowledges that detachment remains a challenge, but he is confident that with the right system, the exhaust can be maintained in the desired state. Meanwhile, plasma physicist and computer modeller Sven Wiesen is tackling the complex, non-linear challenges of fusion, such as managing growing instabilities and long-term issues like the slow erosion of a reactor wall.
Wiesen’s work with high-fidelity models like the Scrape-Off Layer Plasma Simulator (SOLPS) has been instrumental in understanding the many interacting processes at the edge of a fusion reactor. However, the increased pace in the fusion community demands faster, more agile predictions. Wiesen is part of a movement that uses machine learning and artificial intelligence to train surrogate models, which can reproduce the same overall behaviour in minutes instead of months.
These surrogate models open up new possibilities in the world of fusion. Control engineer Thomas Bosman envisions an advanced controller with a fast model of the plasma inside, looking ahead at what the plasma will do and deciding how to tweak conditions to dampen or avoid unwanted behaviour. This predictive capability could be a game-changer for fusion control.
As the fusion community continues to push the boundaries of what’s possible, the work of researchers like Bosman and Wiesen is crucial. Their efforts are not just about setting records; they’re about shaping the future of clean energy. The insights gained from these experiments will inform the development of future fusion power plants, bringing us one step closer to harnessing the power of the Sun as a clean energy source on Earth. The race for fusion is far from over, but with each new discovery, we’re inching closer to a future powered by clean, limitless energy.