Scientists and engineers from eight nations, including Poland, have carried out a project using lasers on the Joint European Torus (JET) to study fusion fuel retention.

Laser Induced Breakdown Spectroscopy (LIBS), an analytical technique that uses a high-powered laser to measure the composition of a material, was deployed using a remotely operated robotics system on JET.

Initial use of the LIBS system detected JET’s fuel mix of tritium and deuterium on the tokamak’s plasma-facing components.

JET provides an ideal engineering and diagnostic testbed for developing technologies to manage tritium inventories in future power plants.

“The experiment was the culmination of several years of efforts to create a method for measuring fuel retention and the accumulation of impurities in the walls of thermonuclear reactors such as ITER. The Institute of Plasma Physics and Laser Microfusion has played an important role in this research from the beginning, which will now focus on developing artificial intelligence models to analyse the LIBS measurements in real time. Due to the numerous unknown factors related to the operation of future fusion power plants, this is certainly a big challenge, but when we started working with LIBS over a decade ago, the successes now achieved at JET seemed no less significant," said Dr. Paweł Gąsior from the Department of Fusion Plasma Research at the IPPLM.

In addition to Polish researchers, teams from Finland, Germany, Italy, Estonia, Latvia, Slovakia and Great Britain also took part in the international cooperation. These countries belong to EUROfusion, a consortium engaged in the research and development of fusion energy.

The project partners include:

• ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development (Italy)
• Forschungszentrum Jülich (Germany)
• VTT Technical Research Centre of Finland Ltd
• United Kingdom Atomic Energy Authority

The work was also supported by:

• Comenius University of Bratislava (Slovakia)
• Institute of Plasma Physics Laser Microfusion, IPPLM (Poland)
• Institute of Solid State Physics, University of Latvia
• University of Tartu (Estonia)

LIBS on JET, Credit: UKAEA

How LIBS technology works

Jari Likonen, Principal Scientist at VTT, explained: “LIBS works by firing a laser beam rapidly at the surface of a tile or component. This generates a small plasma containing atoms, ions and free electrons which emit light that is in turn measured by a spectrometer.”

The LIBS technique is already widely used in industry sectors that involve challenging environments for humans and require rapid, comprehensive chemical analysis at the atomic level. Applications include geological analysis in space exploration, diagnostics of archaeological artifacts, and the study of metal diffusion in solar photovoltaic cells.

For its deployment on JET, modifications were made to adapt the LIBS technology to the facility’s vacuum pressured, donut ringed shaped environment. Salvatore Almaviva, Researcher for Laser-Based Metrology at ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development in Italy, said: “The technology was made compact, lightweight, reliable and robust to perform hundreds of measurements in JET.

The LIBS sensor was mounted on MASCOT, JET’s remotely operated robotic system designed for maintenance, repair and diagnostics tasks within its radioactive environment. Almaviva added, “With a single laser shot, the sensors aim to detect all the chemical elements present in the tile or component being analysed and, within limits, their isotopes.”

Rahul Rayaprolu, from Forschungszentrum Jülich (FZJ) in Germany, elaborated on the data collection process: “The LIBS unit transfers the collected light through a 20-metre-long optical fibre into four high-resolution spectrometers for spectral analysis. One spectrometer provides detailed insights into retained fuel, while a compact broad-range spectrometer simultaneously captures and records the overall spectral overview.”

Ionut Jepu, Materials Research Scientists at the UK Atomic Energy Authority, highlighted the importance of the facility: “JET offers the perfect testbed. Following its recent deuterium-tritium experiments, important measurements of tritium were attempted[GU2] within its tiles and components while reducing the hazard to humans and minimising any shutdown time.”

Over 800 locations within JET’s inner vessel were exposed to the LIBS system. Further details of the project’s results will be presented at the 20th International Conference on Plasma-Facing Materials and Components for Fusion Applications to be held in May 2025 in Slovenia.

The collaborative effort demonstrates the potential for future joint initiatives in the design, safety and operational efficiency of technologies for future fusion machines and exploring fuel retention management.

Source: EUROfusion