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MIT’s nuclear fusion reactor is closer: its 20-tesla superconducting magnet, the most powerful ever created of its kind, is ready

MIT scientists have reached one of the necessary milestones to continue building their promising nuclear fusion reactor. A milestone that allows them to remain optimistic for 2025, the date they have set for the creation of SPARC and later ARC, the most compact and economical alternative to ITER. These days the team of researchers has shown the World’s Most Powerful High Temperature Superconducting Magnet for the creation of the nuclear fusion reactor.

A magnet that has been able to reach a magnetic field of 20 tesla. This is a record-breaking magnetic field capable of lifting the equivalent of SpaceX’s 739 Falcon 9. Although this figure does not allow us to define all the interesting properties of a superconducting magnet for nuclear fusion, we can get an idea of ​​its magnitude if we compare it with the 11.8 teslas of the magnets that will be used in ITER or the 8, 3 teslas that have the magnets used in the LHC particle accelerator.

A powerful superconducting magnet that powers the SPARC reactor

The comparison with ITER is inevitable, although the two major projects to achieve nuclear fusion have a different strategy. In the case of the MIT and Commonwealth Fusion Systems project, its reactor will be a tokamak made up of 18 magnets, equivalent to those that this week have managed to verify that they are capable of stably produce the magnetic field necessary to attempt to efficiently produce energy through nuclear fusion.

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Recreation of the SPARC. Image: T. Henderson, CFS / MIT-PSFC, 2020

With a weight of 9.2 tons and a 3.3 meter radius size, MIT’s superconducting magnet produces a magnetic field up to twelve times stronger than that of an MRI machine, but it does consuming only 30 watts of energy. A ridiculous amount, more so compared to the 200 million watts consumed by traditional copper-wired magnets previously tested by the same team, as described by Dennis Whyte, co-founder of CFS.

ITER magnets will have a less intense magnetic field, but their greater radius (6.2 meters) will allow a larger volume of plasma to be compacted. And is that in the stabilization of plasma is one of the challenges to achieve nuclear fusion. It is a process that is theoretically well studied, but requires high-level engineering to be able to produce a profitable energy reaction.

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Commonwealth Fusion Systems, the MIT engineering firm behind the nuclear fusion reactor, has been working on this project for several years, has received more than $ 250 million and employs more than 150 workers. Its intention is to build its first reactor in 2025 and have the first commercially viable reactors by 2030. Nails dates considerably more optimistic than those set by ITER, a larger and more ambitious project that does not plan to fuse tritium and deuterium nuclei before 2035.

The construction of this new magnet was considered the biggest obstacle to obtaining the nuclear fusion reactor. How did they do it? The solution has been obtained through the use of new superconducting materials. Specifically, the magnet is powered by coils of a high temperature superconducting material called ReBCO (Rare earth barium and copper oxide). A material with which they work at a temperature of 20 Kelvin.

“The magnetic material is only part of the engineering challenge. It must be held in place by a structure that can withstand both extreme temperatures and extreme forces,” explains Brian LaBombard, researcher at Commonwealth Fusion Systems. For this structure to reach 20 teslas it was necessary to cool for two weeks then gradually increase the current through the superconductor. And this is where the “magic” of the superconducting material comes in, since much less energy was lost in this process than with normal copper.

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Stack of superconducting coils. Image: Commonwealth Fusion Systems.

The totals are overwhelming. For MIT’s “little” superconducting magnet they needed 270 kilometers of this superconducting material.

Having a stronger magnetic field will theoretically allow smaller reactors. Again two different strategies to try the goal of generating energy through nuclear fusion.

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The 20 tesla figure is a record for the construction of a superconducting magnet for nuclear fusion, but it does not mean the creation of the strongest magnetic field. The Magnet Lab team managed to reach 32 teslas with a diameter of 34 mm and we saw the record in 2019 with up to 45.5 teslas. Although, the merit of the CFS team is the production of a magnet that they will then have to replicate for the construction of the tokamak.

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“We relied on conventional plasma physics and familiar tokamak designs, but applying a new magnet technology“explains Martin Greenwald, deputy director at the Plasma Science and Fusion Center (PSFC). Although there is still much work ahead, the creation of these magnets is an important step in the pursuit of nuclear fusion energy.

“I am now genuinely optimistic that SPARC can achieve positive net energy, based on the demonstrated performance of the magnets,” concludes Maria Zuber, MIT vice president for research.

More information | MIT
Imagen | Gretchen Ertl, CFS / MIT-PSFC, 2021