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REBCO and MIT superconducting magnets make commercial nuclear fusion realistic by 2030

Nuclear fusion

A comprehensive MIT study of high-temperature superconducting magnets confirms that they meet the requirements for a low-cost, compact fusion power plant.

A detailed report by researchers at PSFC and MIT spinout Commonwealth Fusion Systems (CFS) was published in a collection of six peer-reviewed articles in a special issue of the March issue of IEEE Transactions on Applied Superconductivity.

Superconducting magnets are an essential element for the construction of a nuclear fusion reactor, because they allow the super-heated hydrogen plasma to be concentrated and compressed to the pressure necessary to obtain the fusion itself. The fact that we can have these magnets able to work at temperatures higher than those close to absolute zero, at which they normally work is a factor of enormous importance that paves the way for nuclear fusion in practice.

Together, the documents describe the design and manufacturing of the magnet and the diagnostic equipment needed to evaluate its performance, as well as lessons learned from the process. Overall, the team found that the predictions and computer modeling were correct, verifying that the magnet's unique design elements can serve as the basis for a fusion power plant .

Already on September 5, 2021 , engineers achieved an important milestone in the laboratories of MIT's Plasma Science and Fusion Center (PSFC), when a new type of magnet, made of high-temperature superconducting material, reached an intensity of magnetic field of 20 tesla, world record for a large-scale magnet. This is the intensity needed to build a fusion power plant that would produce net energy and potentially usher in an era of virtually unlimited energy production.

The test was immediately declared a success, having met all criteria established for the design of the new fusion device, called SPARC, for which magnets are the key enabling technology. Champagne corks popped as the exhausted team of experimenters, who had worked long and hard to make the achievement possible, celebrated their achievement.

But this was certainly not the end of the trial. Over the next few months, the team disassembled and inspected the magnet's components, examined and analyzed data from hundreds of instruments that recorded test details, and performed two more tests on the same magnet, finally pushing it to the breaking point to learn details of each possible failure mode.

Enabling practical fusion energy

The success of the magnet test, said Hitachi America engineering professor Dennis Whyte, who recently retired as director of the PSFC, was “the most important thing, in my opinion, of the last 30 years of magneto research. fusion" .

Before the 2021 demonstration, the best superconducting magnets available were powerful enough to potentially achieve fusion energy, but only at sizes and costs that could never be practical or economically viable. Then, when tests demonstrated the feasibility of such a strong magnet at a greatly reduced size, the cost of producing one watt from nuclear fusion was reduced by 40 times. What was an economic nightmare has become a dream.

The comprehensive data and analysis of the PSFC magnet test, as illustrated in the six new papers, demonstrated that plans for a new generation of fusion devices – the one designed by MIT and CFS, as well as similar designs by others Commercial fusion companies – are built on solid scientific foundations.

The superconducting breakthrough

Fusion, the process of combining light atoms to form heavier atoms, powers the sun and stars, but harnessing this process on Earth has proven to be a daunting challenge, with decades of hard work and many billions of dollars spent on experimental devices . The long-sought but never achieved goal is to build a fusion power plant that produces more energy than it consumes. Such a power plant could produce electricity without emitting greenhouse gases during operation and generating very little radioactive waste. Fusion fuel, a form of hydrogen that can be made from seawater, is virtually limitless.

Unfortunately, making it work requires compressing the fuel to extraordinarily high temperatures and pressures, and since no known material can withstand such temperatures, the fuel must be held in place by extremely powerful magnetic fields. Superconducting magnets are needed to produce such strong fields, but all previous fusion magnets have been made of a superconducting material that requires freezing temperatures of about 4º above absolute zero (4 kelvin, or -270º Celsius).

In recent years, a newer material called REBCO (rare earth barium copper oxide) has been added to smelting magnets, allowing them to operate at 20 kelvin, a temperature that, despite being hotter than just 16 kelvin , offers significant advantages in terms of material properties and practical engineering.

To take advantage of this new, higher-temperature superconducting material, it wasn't enough to replace existing magnet designs. Instead, “it was a reworking from scratch of almost all the principles that you use to make superconducting magnets,” Whyte said. The new REBCO material is “strikingly different from the previous generation of superconductors. It's not just about adapting and replacing, but about innovating from the ground up." New papers published in Transactions on Applied Superconductivity describe the details of this redesign process now that patent protection is in effect.

Spherical tokamak, which could benefit significantly from new superconducting magnets

A key innovation: no insulation

One major innovation, which made many others in the industry skeptical of its chances of success, was the elimination of the insulation around the thin, flat ribbons of superconducting tape that formed the magnet. Like virtually all electrical wires, conventional superconducting magnets are fully protected by insulating material to prevent short circuits between the wires. In the new magnet, however, the ribbon has been left completely uncovered; engineers relied on REBCO's increased conductivity to maintain current flow through the material. Electricity flows through the REBCO tapes due to the lower resistance encountered, therefore there is no need to isolate the REBCO tapes from each other.

The fact of being able to avoid insulation layers means that the ordinary construction of magnets, obtained by alternating layers of conductive and insulating material, can be incredibly simplified and lightened, obtaining much more powerful magnets with much lower weights. However, this is a new and potentially dangerous procedure, which must be tested carefully.

The array of magnets is a slightly scaled-down version of those that will form the donut-shaped chamber of the SPARC fusion device, currently under construction at CFS in Devens, Massachusetts. It consists of 16 plates, called pancakes, each of which features a spiral winding of superconducting tape on one side and cooling channels for helium gas on the other.

Push yourself to the limit… and beyond

The initial test, described in previous articles, showed that the design and manufacturing process not only worked, but were also very stable – something some researchers had doubted. The next two tests, also performed in late 2021, pushed the device to its limits by deliberately creating unstable conditions, including completely shutting down incoming power that can lead to catastrophic overheating. Known as quenching, this is considered a worst-case scenario for the operation of these magnets, with the potential to destroy the equipment.

Even during this test, which involved simulating the melting of one of the 16 magnets that made up the complete coil, the magnet managed to continue working equally and the interruption did not lead to the implosion of the entire coil, maintaining the damage at a controlled and limited level.

This test was extremely important because it provides the certainty that traumatic events cannot occur even in the case of anomalies in one of the various REBCO tapes. The realization of these experiments makes MIT's claim to have a commercial experimental facility for nuclear fusion by 2030 realistic.


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The article REBCO and MIT superconducting magnets make commercial nuclear fusion realistic by 2030 comes from Economic Scenarios .


This is a machine translation of a post published on Scenari Economici at the URL https://scenarieconomici.it/i-magneti-superconduttori-rebco-el-mit-rendono-realistica-la-fusione-nucleare-commerciale-entro-il-2030/ on Wed, 06 Mar 2024 10:00:40 +0000.