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New High-Temperature Superconductor (HTS) Cable Demonstrates High Performance

Cambridge, MA – October 7, 2020 – Commonwealth Fusion Systems (CFS), a startup commercializing fusion energy, joined researchers at the MIT Plasma Science and Fusion Center (PSFC) to announce they have designed, built, and demonstrated a new high-temperature superconductor (HTS) cable that can be engineered into magnets directly applicable to the high magnetic field approach to fusion. The findings, published in the journal Superconducting Science and Technology, showed that this new HTS cable, called VIPER, is able to carry high levels of current, exceeding 50 kA, at very high magnetic fields, exceeding 10 T, or about six times stronger than a typical hospital MRI.

“HTS cables have long held promise for fusion energy applications that use high-field electromagnets to strongly confine plasmas, but until now none of the few HTS cable designs in existence have been capable of simultaneously withstanding the extreme currents, field strengths, and mechanical and thermal environments of a fusion device,” said CFS CSO Brandon Sorbom. “This is an exciting and important technological development in our mission to bring commercial fusion energy to the world.”

Certain fusion magnets need to turn on and off continually, and as a result VIPER was tested for thousands of on-off cycles and exhibited minimal performance degradation, despite the extreme electromagnetically induced mechanical forces under operation, exceeding 10,000 PSI. The key innovation in VIPER is its combination of hundreds of individual tapes into a soldered, monolithic block of conductor that enables a high degree of current sharing among tapes, and between tapes and a copper housing. This approach produces highly reproducible behavior even in the presence of large tape-to-tape variations, which is essential to its reliable incorporation into complex engineering systems.

VIPER is also resilient against a common fault condition called “quench” in which a portion of an HTS cable warms up enough to lose its superconducting properties, leading to irreversible damage. Quench in superconducting cables is usually detected by measuring local voltages along the cable length. But this approach is often too slow to catch and halt quench in HTS cables before damage occurs. VIPER integrates fiber optic systems developed by CERN and the Robinson Research Institute in New Zealand to detect and prevent quench much faster than voltage-based techniques. Its design, which incorporates a central cooling channel and generous use of copper stabilizer, is also inherently stable against thermal anomalies.

CFS and PSFC scientists and engineers are currently adapting VIPER cable for use in high-field fusion power plants. A variant of VIPER will be used in an ARPA-E funded program that will produce a fast-ramping, high-field central solenoid magnet capable of initiating and sustaining plasma current in a tokamak device on its own. This novel magnet will significantly reduce the cost and complexity of commercial fusion power plants. It may also be used in the SPARC tokamak, the collaborative project between CFS and MIT’s PSFC on track to be the first device to demonstrate net energy from fusion for the first time in history. Additionally, VIPER cables and variants are expected to find use in other fusion concepts and high-field magnets, aided by their high manufacturability 

About CFS

Commonwealth Fusion Systems (CFS) is on track to bring fusion energy technology to market. CFS was spun out of MIT and is collaborating with MIT’s Plasma Science and Fusion Center to leverage decades of research combined with the innovation and speed of the private sector. CFS has assembled a world-class team working to design and build fusion machines that will provide limitless, clean, fusion energy to combat climate change. Supported by the world’s leading investors in breakthrough energy technologies, this CFS team is uniquely positioned to deliver the fastest path to commercial fusion energy.