Fusion researchers have published a roadmap aimed at predicting how runaway electrons can damage the inner walls of tokamak reactors, a problem described as both cross-disciplinary and time-critical for present and future fusion machines. The roadmap, published in Plasma Physics and Controlled Fusion, seeks to connect runaway electron modelling with plasma-surface interaction and material-damage modelling, areas that have traditionally developed along separate tracks.
Runaway electrons are energetic particles that can be generated during disruptions in tokamaks, and when they strike plasma-facing components they can cause severe material damage. The roadmap identifies the key physics, modelling, experimental and validation challenges that must be addressed to achieve predictive capability for these wall loads and the resulting damage. According to the authors, closer integration of the relevant modelling chains is essential because current approaches do not adequately link the behaviour of runaway electrons to the material response of the components they hit.
The work is presented as a roadmap by S. Ratynskaia, M. Hoelzl, E. Nardon and colleagues, and it highlights the present state of the field while pinpointing the most important gaps in current modelling chains. It also sets out future challenges for ITER and next-step fusion devices, where the consequences of runaway electron damage could be more severe and harder to mitigate than in today's smaller machines.
A webinar accompanying the roadmap will feature four speakers with expertise spanning plasma physics, runaway electron simulation and tokamak experiments. Svetlana Ratynskaia is a professor at the Royal Institute of Technology in Stockholm, Sweden, whose research focuses on plasma-material interactions and tokamak edge plasmas. Her current projects concern damage to plasma-facing components under high transient heat loads such as edge-localized modes, disruptions and runaway electrons, as well as metallic melt generation and motion, emissive sheaths in magnetized plasmas, and powder and dust transport under reactor-relevant conditions.
Chang Liu is an assistant professor in the School of Physics at Peking University. He earned his bachelor's degree from Peking University and his PhD in plasma physics from Princeton University, then worked at the Princeton Plasma Physics Laboratory before 2025. His research focuses on runaway electrons, energetic particles, plasma instabilities and computational methods for magnetic confinement fusion. He developed the runaway electron simulation code QUADRE and is one of the major developers of the M3D-C1 kinetic-MHD code.
Eric Hollmann is a scientist working on fusion energy research whose work is primarily experimental and based dominantly at the DIII-D tokamak in San Diego, USA. He has also assisted with experiments on linear plasma devices and stellarators, and his favourite present research topics are tokamak disruptions and plasma-materials interactions. Mathias Hoppe received his PhD in plasma physics in 2022 from Chalmers University of Technology in Gothenburg, Sweden, with a thesis on runaway electron model development and validation in tokamaks, which was later awarded the EPS 2024 PhD Research Award. After a postdoc at the Swiss Plasma Center in Lausanne, Switzerland, he began a tenure track position as assistant professor in fusion plasma physics at KTH, and he is the lead developer of the DREAM and SOFT codes.
The roadmap appears in Plasma Physics and Controlled Fusion, a monthly journal dedicated to original results on all aspects of plasma physics and associated science and technology. Its editor-in-chief is Jonathan Graves of the University of York, UK, and EPFL, Switzerland. The publication arrives as fusion research intensifies around ITER and other next-step devices, where reliable predictions of wall damage from runaway electrons will be needed to design components that can withstand disruption events.
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