In the quest to harness the power of fusion, scientists are grappling with a formidable challenge: runaway electrons. These high-energy particles, accelerated to near the speed of light, pose a significant threat to the material structures of future fusion reactors, particularly large tokamaks like the European DEMO. A recent study, led by Dr. Francesco Vannini of the Max Planck Institute for Plasma Physics in Garching, Germany, sheds new light on this issue, offering insights that could shape the future of fusion energy.
The research, published in the journal Nuclear Fusion, focuses on the formation, vertical motion, termination, and wall loads of runaway electron (RE) beams in a plausible plasma configuration for the European DEMO fusion power plant. The study uses the JOREK code to perform predictive numerical simulations, providing a detailed look at the complex dynamics of RE beams.
“Runaway electron loads onto material structures are a major concern for future large tokamaks due to the efficient avalanching at high plasma currents,” Vannini explains. “Our work aims to understand and mitigate these loads to ensure the safety and longevity of fusion reactors.”
The study begins with axisymmetric predictions of RE beam formation in a mitigated scenario, where the plasma current is reduced to minimize the risk of runaway electrons. The researchers then simulate the vertical motion of the RE beam due to loss of position control, a phenomenon known as a Vertical Displacement Event (VDE). This is followed by a 3D simulation of the RE beam termination triggered by a burst of magnetohydrodynamic (MHD) activity during the vertical motion. Finally, the researchers calculate the resulting deposition pattern of the REs onto wall structures, assessing the suitability of a possible sacrificial limiter concept for the protection of first wall components.
The findings of this study have significant implications for the commercialization of fusion energy. By understanding the dynamics of runaway electrons and developing effective mitigation strategies, researchers can design safer and more efficient fusion reactors. This, in turn, could accelerate the deployment of fusion power plants, providing a virtually limitless source of clean energy.
The research also highlights the importance of advanced numerical simulations in fusion research. The JOREK code, used in this study, is a powerful tool for predicting the behavior of plasma and runaway electrons in fusion reactors. As fusion technology continues to advance, such tools will become increasingly important for designing and optimizing fusion reactors.
The study, published in Nuclear Fusion, is a significant step forward in the quest to harness the power of fusion. By providing a detailed understanding of runaway electron dynamics, it paves the way for the development of safer and more efficient fusion reactors, bringing us one step closer to a future powered by clean, abundant fusion energy.
