A Decade of Achievement: UK-based TE's Demo4 Completes World-Leading Testing, Validating the Technology for Commercial HTS Magnet Systems
2026-09-09
A decade in the making—hundreds of conversations and thousands of days of effort.
On September 9, UK-based Tokamak Energy (TE) announced that its Demo4 high-temperature superconducting (HTS) magnet system had successfully completed a 14-month test campaign, validating TE's ability to design, manufacture, integrate and operate a complete HTS system. As a core supplier of HTS tape to TE, Shanghai Superconductor worked closely with TE, supplying high-consistency HTS tape in batches for winding the PF (poloidal field) magnets of the Demo4 device. The valuable engineering data and experience accumulated through Demo4 are now being applied to the development of the HTS magnet system for the STEP fusion programme.
Demo4 is a complete all-HTS spherical tokamak fusion magnet system composed of 44 HTS coils, including 14 TF (toroidal field) magnets (made up of 28 HTS coils) and 2 PF (poloidal field) magnets (made up of 16 HTS coils). During the 14-month campaign, the magnet system accumulated about 10,000 hours of operation under different energised states, much of it at high field, reaching a maximum magnetic field of 13.7 T and a toroidal field coil operating current of 5,600 A, across a working temperature range from 77 K to 17 K, while withstanding transverse mechanical stresses of up to 150 MPa.
The test results showed that the HTS magnet system exhibited excellent thermal stability, early quench detection and active cooling, allowing it to effectively avoid quenches. Through fault testing and a forced discharge experiment at 12.5 T, the system demonstrated strong resistance to impact, with no hotspots or performance degradation observed throughout, fully validating the disturbance tolerance of HTS magnet systems under fault conditions.
"Two days before the official announcement, we happened to be at ASC together, and they shared the news with me in person—I was truly so happy for them!" said Zhu Jiamin, President of Shanghai Superconductor, with evident excitement. "Our cooperation with TE dates back to 2017, when we had only just begun mass production and our production level and capacity were still at an early stage. TE brought nuclear fusion applications into our view; the TE team was full of passion for this technology and ignited that passion in our team as well. We did our utmost to meet TE's project requirements and, after multiple rounds of R&D and process iterations, supplied HTS tape suitable for the Demo4 PF coils in batches in 2018 and 2019. At the end of 2022, our team visited TE and could already see the PF coils successfully wound from Shanghai Superconductor's tape. Today, HTS fusion coils are emerging one after another and may not seem so unusual, but in 2022 this was truly rare and deeply impressive. Over all these years, although TE's Demo4 project kept a low profile externally, our technical exchanges never stopped. Watching the TE team push forward steadily step by step, I actually felt quite certain—they would succeed. Now, seeing the fruit of their ten years of effort, I am so happy for them."
"Over the past decade, TE has grown, and so has Shanghai Superconductor. We have each had our low points and our difficulties, but we never gave up and kept moving forward. We may move slowly, yet we can go further—time has become our best friend, and quality our finest achievement."
Since 2017, Shanghai Superconductor has grown into a leading domestic supplier of second-generation HTS tape in mass production. Through supplying large projects at home and abroad, it has accumulated extensive engineering and project supply experience and supporting technical service capabilities. As the company's comprehensive capacity-expansion plan advances in an orderly manner, these experiences and capabilities have also driven the company to further build and improve a complete industrial production, R&D and quality control management system that meets both the requirements of domestic customers and international standards. During this period, the company successfully passed TE's systematic and rigorous audits and reviews of its supplier quality system, and became the only Chinese company among the HTS tape suppliers for the UK's STEP programme, as well as the sole supplier for the STEP TFMC project. In the second half of 2025, Shanghai Superconductor won the contract for the STEP project's 200 km HTS tape (wide tape) and completed delivery quickly and with assured quality by the end of that year. TE is also a partner in the magnet system of the UK's STEP fusion programme. Leveraging its expertise in magnet design and manufacturing, TE has secured a GBP 70 million contract from the UK's UKFE (with a term until March 2029). Shanghai Superconductor and TE will carry out deeper cooperation and exchanges on the STEP project.
The Demo4 test results validated the complete system integration from fusion device design to the HTS magnet system, power supply, control system and quench protection mechanisms, providing highly valuable technical insights for the integration, testing and operation of dozens of high-field fusion HTS magnets worldwide. Shanghai Superconductor will continue to devote itself to the R&D and scaled production of second-generation HTS tape, providing stable and reliable material support for global fusion engineering and projects with high-performance, highly reliable and highly consistent mass-produced HTS tape products, helping to advance the commercialisation of the fusion industry.