In the predawn hours of Sept. 5, 2021, engineers achieved a major milestone in the labs of MIT's Plasma Science and Fusion Center , when a new type of magnet, made from high-temperature superconducting material, achieved a world-record magnetic field strength of 20 tesla for a large-scale magnet. That's the intensity needed to build a fusion power plant that is expected to produce a net output of power and potentially usher in an era of virtually limitless power production.
Before the Sept. 5 demonstration, the best-available superconducting magnets were powerful enough to potentially achieve fusion energy -- but only at sizes and costs that could never be practical or economically viable. Then, when the tests showed the practicality of such a strong magnet at a greatly reduced size,"overnight, it basically changed the cost per watt of a fusion reactor by a factor of almost 40 in one day," Whyte says.
Taking advantage of this new higher-temperature superconducting material was not just a matter of substituting it in existing magnet designs. Instead,"it was a rework from the ground up of almost all the principles that you use to build superconducting magnets," Whyte says. The new REBCO material is"extraordinarily different than the previous generation of superconductors. You're not just going to adapt and replace, you're actually going to innovate from the ground up.
But the no-insulation design was considered risky, and a lot was riding on the test program."This was the first magnet at any sufficient scale that really probed what is involved in designing and building and testing a magnet with this so-called no-insulation no-twist technology," Hartwig says."It was very much a surprise to the community when we announced that it was a no-insulation coil.
Whyte says,"Basically we did the worst thing possible to a coil, on purpose, after we had tested all other aspects of the coil performance. And we found that most of the coil survived with no damage," while one isolated area sustained some melting."It's like a few percent of the volume of the coil that got damaged." And that led to revisions in the design that are expected to prevent such damage in the actual fusion device magnets, even under the most extreme conditions.