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Smaller, stronger magnets could improve devices that harness the fusion power of the sun and stars

Smaller, stronger magnets could improve devices that harness the fusion power of the sun and stars

PPPL chief engineer Yuhu Zhai showing images of a high-temperature superconducting magnet, which could improve the performance of spherical tokamak fusion devices. Credit: Kiran Sudarsanan/PPPL Office of Communications

Researchers at the U.S. Department of Energy (DOE) Princeton Plasma Physics Laboratory (PPPL) have found a way to build powerful magnets that are smaller than before, aiding the design and construction of machines that could help the world harness the power of the sun to generate electricity without producing greenhouse gases that contribute to climate change.

The scientists have found a way to build high-temperature superconducting magnets made of material that conduct electricity with little or no resistance at temperatures warmer than before. Such powerful magnets would fit more easily into the cramped space in spherical tokamaks, which are more like an apple core than the doughnut-like shape of conventional tokamaks, and are being explored as a possible design for future fusion power plants.

Because the magnets could be placed in the central cavity of the spherical tokamak separately from other machines to corral the hot plasma that fuels fusion reactions, researchers were able to fix them without taking anything else apart.

“To do this, you need a magnet with a stronger magnetic field and a smaller size than current magnets,” said Yuhu Zhai, a chief engineer at PPPL and lead author of a paper reporting the results in IEEE Transactions on Applied Superconductivity. “You only do that with superconducting wires, and that’s what we did.”

Fusion, the force that drives the sun and stars, combines light elements in the form of plasma — the hot, charged state of matter made up of free electrons and atomic nuclei — generating enormous amounts of energy. Scientists are trying to simulate fusion on Earth for a virtually inexhaustible supply of safe and clean energy to generate electricity.

High temperature superconducting magnets have several advantages over copper magnets. They can last longer than copper magnets because they don’t heat up as quickly, making them better suited for use in future fusion plants that have to run for months at a time. Superconducting wires are also powerful and can transfer the same amount of electrical current as a copper wire, many times wider, while producing a stronger magnetic field.

The magnets could also help scientists reduce the size of tokamaks, improve performance and reduce construction costs. “Tokamaks are sensitive to conditions in their central regions, including the size of the central magnet or solenoid, the shield and the vacuum vessel,” said Jon Menard, PPPL’s ​​deputy director for research. “A lot depends on the center. So if you can shrink things in the middle, you can shrink the whole machine and reduce costs, while theoretically improving performance.”

These new magnets use a technique refined by Zhai and researchers at Advanced Conductor Technologies, the University of Colorado, Boulder, and the National High Magnetic Field Laboratory in Tallahassee, Florida. The technique means that the wires do not require conventional epoxy and fiberglass insulation to ensure the flow of electricity. The technology simplifies construction, but also reduces costs. “The cost of winding the coils is much lower because we don’t have to go through the expensive and error-prone epoxy vacuum impregnation process,” Zhai said. “Instead, you wind the conductor directly into the coil form.”

In addition, “superconducting magnets at high temperatures can aid in the spherical tokamak design because the higher current density and smaller windings provide more space for a support structure that helps the device withstand the high magnetic fields, improving operating conditions,” says Thomas Brown , a PPPL engineer who contributed to the research. “In addition, the smaller, more powerful magnets give the machine designer more options to design a spherical tokamak with a geometry that could improve the overall tokamak performance. We’re not quite there yet, but we’re closer, and maybe close.” enough.”

Innovative new magnet can facilitate the development of fusion and medical devices

More information:
Y. Zhai et al, HTS Cable Guide for Compact Fusion Tokamak Solenoids, IEEE Transactions on Applied Superconductivity (2022). DOI: 10.1109/TASC.2022.3167343

Provided by Princeton Plasma Physics Laboratory

Quote: Smaller, stronger magnets could improve devices that harness the fusion power of the sun and stars (July 2022, July 25) retrieved July 25, 2022 from https://phys.org/news/2022-07-smaller-stronger-magnets- devices -harness.html

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