News Release

- A Major Step Toward the Start of ITER Operations -

One of the world’s largest superconducting^※1 toroidal field (TF) coils manufactured by the National Institutes for Quantum Science and Technology (QST) and Toshiba Corporation has successfully passed excitation testing under cryogenic conditions at -269°C. The test replicates the actual operating conditions of the ITER^※2 nuclear fusion reactor, and marks a major step toward start of operation of ITER.

The TF coil is one of the most critical components of ITER, the generator of the powerful magnetic field required to confine the plasma. As ITER moves toward the start of operations, a key technical challenge for the project's success is to strengthen the reliability of the integrated system through testing in conjunction with the power supply and cryogenic plant.

In collaboration with the ITER Organization, the TF coil was cooled from room temperature to its operating temperature of -269°C, confirming its transition to the superconducting state. The coil was then successfully energized up to 10,000 amperes for the first time under superconducting conditions. This is the first successful excitation test of an ITER TF coil under superconducting operating conditions. The results validated the manufacturing method used to produce a large-scale coil employing niobium-tin (Nb₃Sn) superconducting conductors, which are highly sensitive to strain. The test also provided key data required to ensure stable operation under cryogenic conditions, including resistive heating at conductor joints and coolant flow characteristics at low temperatures. Both were confirmed to be within the design expectations. Furthermore, no abnormalities, such as coolant leakage during cool-down or energization, were observed, confirming the integrity of the TF coil.

TF coil experts dispatched by QST played a key role in the implementation of the test. Working closely with the ITER Organization and drawing on expertise gained through the manufacture of the TF coils, they led the development of the test plan and contributed significantly to its successful execution.

This achievement demonstrates that Japan possesses world-leading core technologies for large-scale superconducting coils, which are essential for the development of fusion energy. The test also represents a major step toward the start of ITER operations. By supporting the establishment of operating procedures, the training of operators, and the identification of technical issues for risk mitigation, the test will contribute significantly to the integrated commissioning of the ITER superconducting magnet system and help reduce risks associated with future operations.

• Superconductivity is a phenomenon in which certain materials, known as superconductors, exhibit zero electrical resistance when cooled to extremely low temperatures. By exploiting this phenomenon and using superconducting materials as conductors carrying large currents, it is possible to generate extremely powerful magnetic fields.
  The superconducting conductor used for the TF coils consists of a cable made by cabling together 900 superconducting strands and 522 copper strands, each 0.82 mm in diameter, and enclosing the cable in a stainless-steel jacket. The superconducting material is niobium-tin (Nb₃Sn), which becomes superconducting when cooled below −255°C.
• Japan is contributing to the ITER Project, a global collaboration among 34 countries also representing one of the seven members, aimed at demonstrating the scientific and technological feasibility of fusion energy through the construction and operation of ITER. At the construction site in Saint-Paul-lez-Durance in southern France, assembly of key components is progressing steadily toward the commencement of operations, while the manufacturing of ITER components by the participating members continues to advance successfully.
  URL: https://www.fusion.qst.go.jp/ITER/english/iter.html (English)

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