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Advancing Fusion Energy: High-Field REBCO Superconducting Magnets in the SPARC TFMC Program


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Feb 16, 2024
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Superconductivity is a phenomenon where certain materials can conduct electricity with zero resistance when cooled below a certain temperature. This property can lead to highly efficient power transmission systems and has significant implications for clean energy technologies. Fusion energy seeks to mimic the Sun’s power generation mechanism on Earth by fusing light atomic nuclei, such as hydrogen, to form heavier nuclei, releasing vast amounts of energy in the process. Both technologies face significant technical and engineering challenges. For superconductivity, the main challenge lies in developing materials that can operate at higher temperatures to reduce cooling costs. For fusion energy, achieving a sustained, controlled fusion reaction that produces more energy than it consumes remains a monumental task. Despite these challenges, advances in materials science, engineering, and plasma physics are steadily pushing these technologies closer to commercial viability. Applied superconductivity is already enhancing the efficiency of various applications, and although fusion energy is likely still decades away from being a practical power source, its potential as a clean, inexhaustible energy source makes it a crucial area of research in our quest for sustainable energy solutions. The integration of applied superconductivity in fusion reactors exemplifies how these technologies can synergize to unlock new possibilities in clean energy. The successful development and deployment of fusion energy, supported by advances in superconductivity, could dramatically reduce our reliance on fossil fuels, mitigate climate change, and secure a clean, abundant energy future for generations to come. The SPARC Toroidal Field Model Coil (TFMC) Program, led by Professor Zachary Hartwig of the MIT Plasma Science and Fusion Center, the authors focused on the development and demonstration of high-field superconducting magnets using rare earth barium copper oxide (REBCO) technology. The program aimed to address the design, fabrication, and operational risks associated with large-scale, high-field superconducting magnets, which are crucial for the advancement of fusion energy technologies. The new study is now published in IEEE Transactions on Applied Superconductivity.

Before the authors conduct a full-scale testing, the program undertook an extensive review of the design and fabrication processes of the TFMC. This included validating the novel REBCO superconductor technologies developed during the program, assessing the manufacturing techniques for the coil, and ensuring that all components met the stringent requirements necessary for high-field operation in a fusion reactor. The validation process confirmed the program’s capability to produce a high-quality, high-field superconducting magnet, setting the stage for experimental testing. The core experiment of the TFMC Program was the high-field performance test, where the TFMC achieved a peak field-on-conductor of 20.1 T at a terminal current of 40.5 kA. This experiment not only demonstrated the TFMC’s capability to achieve high magnetic fields, essential for efficient plasma confinement in fusion reactors, but also validated the theoretical and computational models used in the magnet’s design. The successful achievement of high-field conditions confirmed the potential of REBCO superconductors in enabling compact and efficient fusion reactor designs. Another critical aspect of the experiments was assessing the TFMC’s ability to withstand the mechanical stress and Lorentz loading, which are significant in the operational environment of a fusion reactor. The TFMC was subjected to almost 1 GPa of mechanical stress and 815 kN/m of Lorentz loading on the REBCO stacks. The coil’s structural case, designed to accommodate these loads, was rigorously tested and performed within expected parameters. This experiment demonstrated the TFMC’s robustness and reliability under the extreme conditions present in fusion reactors.

The team tested the TFMC Program and a novel cryogenic cooling scheme designed to remove the large amount of heat generated during operation. This scheme utilized a parallel, single-pass, pressure-vessel style coolant approach, which was experimentally validated during the testing campaigns. The cooling system’s effectiveness in maintaining the magnet’s temperature within operational limits under high current and high magnetic field conditions was confirmed supporting the feasibility of using such cooling methods for large-scale, high-field superconducting magnets in fusion reactors. Moreover, the program conducted tests to evaluate the electromagnetic performance of the magnet, including dc and ac characteristics, and the effectiveness of its passive self-protection mechanism against quenches, a sudden loss of superconductivity that can lead to rapid temperature rises and potential damage. The TFMC successfully demonstrated passive self-protection during a controlled quench event, despite not being optimized for quench resiliency. The experimental assessment of passive, self-protection against a quench in the fusion-scale NI TF coil was a significant step toward understanding and managing quench scenarios in high-field superconducting magnets. Furthermore, a unique feature of the TFMC was its fifteen internal demountable pancake-to-pancake joints, designed to operate within the 0.5 to 2.0 nΩ range at 20 K and in magnetic fields up to 12 T. The performance of these joints was critically assessed and found to meet the operational requirements, demonstrating the feasibility of using such joints in the construction and maintenance of large-scale superconducting magnets for fusion energy applications.

The authors found TFMC’s successful operation at 20.1 T peak field-on-conductor confirmed the high-field capability of REBCO superconductors, supporting their use in compact, efficient fusion reactor designs. Additionally, the coil withstood nearly 1 GPa of mechanical stress and significant Lorentz loading, validating the structural design and material selection for high-field magnet applications in fusion energy. They also validated the novel cryogenic cooling scheme, demonstrating the system’s capability to manage the heat loads expected in operational fusion reactors effectively. The experimental assessment of passive self-protection mechanisms against quenches provided valuable insights into managing such events in high-field superconducting magnets. Furthermore, the internal demountable joints’ successful operation highlighted the potential for modular construction and maintenance strategies in future fusion reactor magnet systems.

The program successfully developed novel superconductor technologies, confirming the high-fidelity computational models through extensive testing, and validating a new coolant scheme capable of significant heat removal represent substantial progress in the superconducting magnet field. Particularly noteworthy is the exploration of passive self-protection mechanisms against quenching in fusion-scale no-insulation (NI) TF coils. This aspect is critical for ensuring the safety and reliability of superconducting magnets in fusion energy systems. Furthermore, the TFMC Program has significantly impacted the superconducting materials industry, driving down the cost of REBCO tape and fostering advancements in manufacturing and characterization techniques. This economic effect facilitates broader adoption and further development of REBCO-based technologies across various applications, beyond fusion energy. In summary, the SPARC TFMC Program, led by Professor Zachary Hartwig and his team, has made significant advancements to the field of applied superconductivity and fusion energy. By successfully demonstrating the capabilities of high-field REBCO magnets, the program paves the way for the next steps in fusion energy development, moving closer to the realization of fusion as a clean, abundant, and sustainable energy source.

Advancing Fusion Energy: High-Field REBCO Superconducting Magnets in the SPARC TFMC Program - Advances in Engineering

CAD rendering of the TFMC magnet showing the principal components.


About the author​

Zachary Hartwig

Robert N. Noyce Career Development Professor
Department of Nuclear Science and Engineering
Massachusetts Institute of Technology

Zachary (Zach) Hartwig is the Robert N. Noyce Career Development Professor at MIT and an Associate Professor in the Department of Nuclear Science and Engineering (NSE) with a co-appointment at the MIT Plasma Science and Fusion Center (PSFC). He has worked primarily in the areas of large-scale applied superconductivity, magnet fusion device design, and plasma-material interactions with additional activities in nuclear security, radiation detector development, Monte Carlo particle transport simulation, and accelerator science and engineering. His active research focuses primarily on the development of high-field superconducting magnet technologies for fusion energy and accelerated irradiation methods for fusion materials using ion beams.​


Zachary S. Hartwig, Rui F. Vieira, Darby Dunn, Theodore Golfinopoulos, Brian LaBombard, Christopher J. Lammi, Philip C. Michael, Susan Agabian, David Arsenault, Raheem Barnett, Mike Barry, Larry Bartoszek, William K. Beck, David Bellofatto, Daniel Brunner, William Burke, Jason Burrows, William Byford, Charles Cauley, Sarah Chamberlain, David Chavarria, JL Cheng, James Chicarello, Van Diep, Eric Dombrowski, Jeffrey Doody, Raouf Doos, Brian Eberlin, Jose Estrada, Vincent Fry, Matthew Fulton, Sarah Garberg, Robert Granetz, Aliya Greenberg, Martin Greenwald, Samuel Heller, Amanda E. Hubbard, Ernest Ihloff, James H. Irby, Mark Iverson, Peter Jardin, Daniel Korsun, Sergey Kuznetsov, Stephen Lane-Walsh, Richard Landry, Richard Lations, Rick Leccacorvi, Matthew Levine, George Mackay, Kristen Metcalfe, Kevin Moazeni, John Mota, Theodore Mouratidis, Robert Mumgaard, JP Muncks, Richard A. Murray, Daniel Nash, Ben Nottingham, Colin O’Shea, Andrew T. Pfeiffer, Samuel Z. Pierson, Clayton Purdy, Alexi Radovinsky, Dhananjay K. Ravikumar, Veronica Reyes, Nicolo Riva, Ron Rosati, Michael Rowell, Erica E. Salazar, Fernando Santoro, Akhdiyor Sattarov, Wayne Saunders, Patrick Schweiger, Shane Schweiger, Maise Shepard, Syun’ichi Shiraiwa, Maria Silveira, FT Snowman, Brandon N. Sorbom, Peter Stahle, Ken Stevens, Joshua Stillerman, Deepthi Tammana, Thomas L. Toland, David Tracey, Ronnie Turcotte, Kiran Uppalapati, Matthew Vernacchia, Christopher Vidal, Erik Voirin, Alex Warner, Amy Watterson, Dennis G. Whyte, Sidney Wilcox, Michael Wolf, Bruce Wood, Lihua Zhou, Alex Zhukovsky. The SPARC Toroidal Field Model Coil Program. IEEE Transactions on Applied Superconductivity, 2024; 34 (2): 1 DOI: 10.1109/TASC.2023.3332613

Go to IEEE Transactions on Applied Superconductivity
The post Advancing Fusion Energy: High-Field REBCO Superconducting Magnets in the SPARC TFMC Program appeared first on Advances in Engineering.
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