Smaller and more powerful magnets can enhance devices that harness the fusion power of the sun and stars
PPPL main engineer Yuhu Zhai with high temperature superconducting magnet drawing, which can improve the performance of spherical tokamak fusion device. Credit: Kiran Sudarsanan / PPPL Transportation Service
Researchers at the US Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have found a way to build powerful magnets that are smaller than ever, helping design and construct machines that can help the world harness the power of the sun to create electricity. without producing the greenhouse gases that contribute to climate change.
Scientists have found a way to build high-temperature superconducting magnets made of materials that conduct electricity with little or no resistance at warmer temperatures than before. Such a powerful magnet would fit more easily into the tight spaces inside the spherical tokamak, which is shaped more like a nucleated apple than a conventional donut tokamak, and is being explored as a possible design for future fusion power plants.
Because the magnets can be positioned apart from other machines in the spherical tokamak’s central cavity to hold the hot plasma that triggers the fusion reaction, the researchers were able to fix it without having to disassemble anything.
“To do this, you need a magnet with a stronger magnetic field and a smaller size than the current magnet,” said Yuhu Zhai, a principal engineer at PPPL and lead author of the paper reporting the results in IEEE Transactions on Applied Superconductivity. “The only way you can do that is with superconducting cables, and that’s what we’ve done.”
Fusion, the force that drives the sun and stars, combines light elements in the form of plasma—a hot-charged state of matter composed of free electrons and atomic nuclei—which produces large amounts of energy. Scientists are trying to replicate fusion on Earth for a safe and clean supply of almost endless electricity to generate electricity.
High temperature superconducting magnets have several advantages over copper magnets. They can be kept on for a longer time than copper magnets because they don’t heat up as quickly, making them more suitable for use in future fusion power plants that have to run for months at a time. Superconducting wires are also strong, being able to transmit the same amount of electric current as copper wires many times wider while producing a stronger magnetic field.
Magnets can also help scientists continue to shrink tokamaks in size, improve performance and reduce construction costs. “Tokamak is sensitive to conditions in its central region, including the size of the central magnet, or solenoid, shield, and vacuum housing,” said Jon Menard, deputy director of PPPL 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, in theory, improving performance.”
The new magnet utilizes a technique refined by Zhai and researchers at Advanced Conductor Technologies, University of Colorado, Boulder, and the National High Magnetic Field Laboratory, in Tallahassee, Florida. This technique means that the cable does not require conventional epoxy and glass fiber insulation to ensure the flow of electricity. Apart from simplifying construction, this technique also lowers costs. “The cost to spin the coil is much lower because we don’t have to go through the expensive and error-prone process of vacuum epoxy impregnation,” says Zhai. “Instead, you directly wind the conductor into a coil.”
In addition, “high-temperature superconducting magnets can aid the design of spherical tokamaks because the higher current density and smaller windings provide more room for the supporting structure that helps the device withstand high magnetic fields, improving operating conditions,” said Thomas Brown, an engineer. PPPL who contributed to the research. “Also, the smaller and more powerful magnets give the machine designer more options for designing spherical tokamaks with geometries that can improve the overall performance of the tokamaks. We’re not quite there yet but we are closer, and maybe close enough.”
Innovative new magnets can facilitate development of fusion and medical devices
Y. Zhai et al, HTS Cable Conductor for Compact Fusion Tokamak Solenoid, IEEE Transactions on Applied Superconductivity (2022). DOI: 10.1109/TASC.2022.3167343
Provided by Princeton Plasma Physics Laboratory
Quote: Smaller, more powerful magnets could boost devices that harness the fusion power of the sun and stars (2022, 25 July) retrieved 26 July 2022 from https://phys.org/news/2022-07-smaller-stronger-magnets-devices -harness.html
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