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

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

Scientists found a way to build high temperature superconducting magnets they are made of material that conducts electricity with little or no resistance to warmer temperatures than before. These powerful magnets would fit more easily in the small space inside spherical tokamakswhich are more similar in shape to a cored apple than the doughnut-shaped of conventional tokamaks, and are being explored as a possible design for future fusion power plants.

Since the magnets could be placed separate from other machinery in the central cavity of the spherical tokamak to corral the hot plasma that feeds fusion reactionsthe researchers were able to repair them without having to take 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, principal engineer at PPPL and lead author of a paper reporting the results in IEEE Transactions on Applied Superconductivity. “The only way to do it is with superconducting wiresAnd that is what we have done”.

Fusion, the power 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, which generates massive amounts of energy. Scientists seek to replicate fusion on Earth for a virtually inexhaustible supply of safe, clean energy to generate electricity.

High temperature superconducting magnets have several advantages over copper magnets. They can be turned on for longer periods than copper magnets because they don’t heat up as quickly, making them more suitable for use in future fusion power plants that will have to run for months. Superconducting cables are also powerful, capable of transmitting the same amount of electrical current as a much wider copper wire, while producing a stronger magnetic field.

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

These new magnets take advantage of 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 the cables don’t need conventional epoxy and fiberglass insulation to ensure the flow of electricity. While it simplifies construction, the technique also cuts costs. “Costs to wind the coils are much lower because we don’t have to go through the costly and error-prone process of vacuum impregnation with epoxy,” Zhai said. “Instead, you’re directly winding the conductor into a coil.”

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