In the early hours of September 5, 2021, engineers at MIT’s Plasma Science and Fusion Center (PSFC) achieved a groundbreaking milestone by demonstrating a world-record magnetic field strength of 20 tesla with a new high-temperature superconducting magnet. This breakthrough is crucial for advancing fusion power technology, with the potential to usher in an era of virtually limitless energy.

The test of the new magnet was declared a resounding success as it met all the design criteria for the SPARC fusion device, which relies on these advanced magnets as a key component. The team’s accomplishment was the result of extensive preparation, including rigorous testing and analysis. This involved not only reaching the record-breaking magnetic field but also subjecting the magnet to extreme conditions to uncover potential failure modes and ensure its reliability.

The results of these tests were comprehensively detailed in a special edition of IEEE Transactions on Applied Superconductivity published in March. This edition features six peer-reviewed papers that cover the magnet’s design, fabrication, and diagnostic evaluation. These papers confirm that the new design is a solid foundation for the next generation of fusion power plants, highlighting the effectiveness of the high-temperature superconductors used and the overall system’s performance.

Dennis Whyte, Hitachi America Professor of Engineering, emphasized the significance of this achievement, referring to it as “the most important development in the last 30 years of fusion research.” Prior to this breakthrough, superconducting magnets were powerful enough to support fusion energy but were prohibitively large and costly. The new magnet’s compact size and reduced cost have transformed the economics of fusion energy, significantly lowering the cost per watt of fusion reactors and making them more feasible.

Fusion, the process that powers the sun and stars, involves combining light atoms into heavier ones. Replicating this on Earth has been an immense challenge, requiring materials that can withstand extreme temperatures and pressures. Traditional superconducting magnets operate at temperatures around 4 kelvins, but the new material, REBCO (rare-earth barium copper oxide), operates effectively at 20 kelvins. Although this temperature is only 16 kelvins warmer, REBCO offers substantial advantages in terms of its material properties and practical engineering.

The integration of REBCO into magnet designs necessitated a fundamental redesign of conventional principles. One major innovation was the elimination of insulation around the superconducting tape, a move initially met with skepticism. Engineers relied on REBCO’s superior conductivity to maintain current flow without insulation, which simplified the fabrication process and addressed high-voltage issues.

The magnet assembly, a scaled-down model of those planned for the SPARC device, comprises 16 plates. Each plate features a spiral winding of superconducting tape and cooling channels for helium gas. The no-insulation design, while considered risky, proved successful during testing, demonstrating the stability and effectiveness of the new approach.

The test program included pushing the magnet to its limits, including creating quenching events where the magnet overheats. This approach was essential for gathering critical data to validate design models and understand the magnet’s behavior under extreme conditions. Despite the risks, these tests provided valuable insights, confirming the magnet’s performance and identifying areas for further improvement.

The final test revealed that most of the magnet survived with minimal damage, leading to design revisions expected to enhance durability in future devices. This success was attributed to the extensive expertise and infrastructure at PSFC, coupled with effective collaboration between MIT and Commonwealth Fusion Systems (CFS) (CSA, CSM).

The partnership between MIT and CFS combined academic and industrial strengths, with CFS playing a crucial role in scaling up the supply chain for the magnet’s critical materials. This collaboration was key to achieving the project’s ambitious goals and showcased the benefits of integrating academic research with industrial capabilities to drive technological innovation.

The successful demonstration of the 20-tesla magnet represents a significant advancement in fusion research. This achievement paves the way for the development of practical and economically viable fusion power plants.

The innovations introduced, particularly the use of high-temperature superconductors and the no-insulation design, mark a major leap forward in the field, with the potential to revolutionize energy production and bring us closer to a future where fusion power becomes a reality.

Image: A team lowers the magnet into the cryostat container. Credit: Gretchen Ertl

Source: MIT News