ITER to Monitor Extreme Plasma Conditions with Advanced Optical Technology
Inside ITER, the world’s largest fusion experiment, plasma is expected to reach a staggering 150 million degrees Celsius—ten times hotter than the core of the Sun. Monitoring the components exposed to this intense environment is critical, and a cutting-edge optical system called the Wide-Angle Viewing System (WAVS) will be key in enabling scientists and engineers to do so.
Part of Europe’s contribution to ITER’s diagnostic systems, the WAVS will observe both visible and infrared light emitted from the reactor’s divertor and inner chamber walls. This optical data will provide real-time surface temperature readings, helping operators identify any areas in danger of overheating and take preventive action to protect the equipment.
The WAVS system is composed of 15 lines of sight, strategically positioned across four vacuum vessel ports, enabling it to monitor approximately 80% of ITER’s inner surfaces. Each line of sight collects light through an entrance pupil. The light is then transmitted via a sequence of precision mirrors and lenses to a set of cameras housed in the port cells. This complex arrangement includes more than 600 opto-mechanical components, 60 cameras, and various auxiliary devices.
Fusion for Energy (F4E), the EU body overseeing Europe’s contribution to ITER, is leading the design of the 15 WAVS lines and the procurement of 11 of them. To accelerate the development process, F4E purchased pre-shaped raw materials in 2023 from German supplier Rolf Kind. More recently, F4E awarded a contract to a consortium known as EBA—comprising Empresarios Agrupados, Bertin Technologies, and AVS—to begin manufacturing key port plug components.
Among the initial components are three “first mirror units,” which play a crucial role by capturing and redirecting incoming light into the system. While the optical principles behind these units are standard, their design had to be adapted for the harsh conditions inside the ITER reactor. To withstand such an environment, the mirrors will be equipped with thermohydraulic cooling circuits and coated with rhodium, which enhances durability and reflectivity.
In December 2022, tests performed at INTA (the Spanish National Institute for Aerospace Technology) on a mirror prototype exposed to thermal cycling showed no loss in reflectivity or degradation of the coating—validating the effectiveness of the design.
These achievements stem from over a decade of collaborative research involving major European scientific institutions such as CEA (France), CIEMAT (Spain), INTA, SCK CEN (Belgium), KIT (Germany), and the industrial partner Bertin. “We conducted comprehensive material evaluations, R&D programs, and prototyping,” said Frédéric Le Guern, Project Manager at F4E. “Together, we’ve developed robust solutions to address some of the most critical challenges in the system.”
One such challenge was the risk of the first mirrors becoming obscured by particle deposits. To tackle this, F4E partnered with the University of Basel in Switzerland to develop an innovative in-situ cleaning method called radio frequency cleaning. This technique uses a localized plasma to clean the mirror surfaces without removing them from the system, maintaining optimal performance over time.
Looking forward, F4E, the ITER Organization, and their partners have taken steps to anticipate potential challenges during manufacturing. According to Le Guern, this strong collaboration has been vital. “Our joint planning has given everyone the confidence needed to move into production. We’re excited about progressing to the next stage.”
With the WAVS moving steadily from design to implementation, it stands as a hallmark of international cooperation and technological innovation—key elements in the mission to make fusion energy a reality.
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