Japan Completes Cryogenic Test of World's Largest Superconducting Toroidal Field Coil for ITER

Japan's National Institutes for Quantum Science and Technology (QST) and Toshiba Corporation announced on August 25 that they had successfully completed the first cryogenic current test of the world's largest superconducting toroidal field coil at the construction site of the International Thermonuclear Experimental Reactor (ITER). The test was conducted at an operating temperature of approximately minus 269 degrees Celsius, marking a critical technical milestone before ITER's commissioning.

The superconducting toroidal field coil installed in the test facility

The toroidal field coil, also known as the TF coil, is a key component of ITER's superconducting magnet system, used to generate the strong magnetic field required to confine plasma. During the test, the team cooled the coil from room temperature to cryogenic conditions, confirmed its transition to the superconducting state, and for the first time achieved stable conduction of 10,000 amperes of current while the coil was in the superconducting state.

The test also validated the effectiveness of the manufacturing process for large coils using strain-sensitive niobium-tin superconducting conductors. The team simultaneously acquired critical data required for cryogenic operation, including joint resistance heat generation and cryogenic refrigerant flow characteristics. According to the announcement, all relevant values fell within the expected ranges from the design phase; during coil cooling and current application, no faults such as refrigerant leakage were detected, and the coil's integrity was confirmed.

ITER's superconducting magnet system measures approximately 30 meters in diameter, weighs approximately 10,000 tons in total, and consists of 18 D-shaped TF coils arranged toroidally. A single TF coil is 16.5 meters high, 9.2 meters wide, and weighs approximately 310 tons, comprising the winding pack and the support structure. Its winding pack is designed to generate a maximum magnetic field of 11.8 tesla, with the straight section bearing electromagnetic forces equivalent to approximately 60,000 tons.

Under the ITER project work-sharing arrangement, Japan is responsible for manufacturing 25% of the TF conductors, all 19 TF structures, and 9 TF coils. QST signed the TF coil procurement agreement with the ITER Organization in 2008, subsequently collaborated with industry partners on development, and completed the manufacturing of 9 TF coils in 2023.

This cryogenic current test provides operational data for subsequent integrated testing and commissioning of ITER's superconducting coil system, and also contributes to refining operating procedures, training operators, and identifying potential risks in advance. QST stated that this achievement demonstrates that Japan has established the engineering foundation in large superconducting coil manufacturing and cryogenic operation technology to support fusion energy research and development.

ITER fusion experimental reactor main body and TF coils

Structure of the TF coil

Completed TF coil