A surgical assembly to upgrade LIPAc

Europe and Japan are progressing in the validation of technologies for the International Fusion Materials Irradiation Facility (IFMIF). One of the key joint projects within the Broader Approach agreement is LIPAc, a prototype accelerator in Rokkasho (Japan) that will help recreate the intense radiation inside a fusion reactor.

After closing a successful round of beam operations, engineers are concentrating on the next component for LIPAc: the Superconducting Radio Frequency (SRF) linear accelerator. Once integrated with the others, this high-energy section will speed a beam of 125 mA up to 9 MeV, aiming to reach continuous waves (CW). It will be a ground-breaking performance for a superconducting accelerator. The goal is now a crucial step closer, as the European teams have completed the clean room assembly, under the coordination of Fusion for Energy (F4E). It's a big accomplishment for them, who knew that only flawless execution was acceptable.

The core of the SRF system is a string of cavities operating at ultra-high vacuum and cryogenic temperatures to generate the electromagnetic fields that accelerate the beam with precision and unprecedented power. However, their performance is a delicate matter. Even the smallest contamination could decrease the performance or cause disruptions.

The assembly required meticulous procedures, specialized skills and an environment where no unwanted particle floats loose. Inside the clean room, the technicians from Research Instruments, F4E's contractor, wore their suits, gloves and masks to assemble the cavities with surgical care. Later, the integrated tests with the vacuum pumping line confirmed the system met airtight standards.

The Superconducting Radio Frequency linear accelerator ready for the last assembly stages outside the clean room. ©F4E

The most critical chapter is now closed, and the teams are ready for the next phase. The components will soon be integrated with the cryogenic systems (that will keep them cooled at -269 ºC) and inserted into the cryostat, a shield structure to maintain the cold temperature. The transport of the 15-tonne SRF line to the LIPAc vault is planned for early next year. It's only a 500 m commute, but with the harsh northern-Japanese winter looming, the teams have prepared a protective structure to secure it.

The integration of the SRF accelerator to the LIPAc beamline and its operation, expected by 2026, will be "the culmination of years of design, manufacturing, tests, and collaboration between multiple international stakeholders," claims Hervé Dzitko, Programme Manager of the EU Home Team and head of the Accelerator Science and Technology group at F4E. His team has worked closely with QST, host of LIPAc, and the European laboratories CEA and CIEMAT, that provided all the SRF components. "The success underlines the technical excellence and the fruitful teamwork by the Japanese and European teams," added Yann Carin, Project Leader of IFMIF/EVEDA.

For the European and Japanese fusion communities, the progress of LIPAc is always encouraging news. The accelerator prototype serves as a demonstrator and is paving the way for future facilities like IFMIF-DONES, that will test the materials for next-generation fusion power plants.

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