In order to design and build machines that could help the world harness the power of the sun to create electricity without producing greenhouse gases that contribute to climate change, researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have discovered a way to build strong magnets smaller than before.
A method was developed by the researchers to create high-temperature superconducting magnets made of a substance that conducts electricity with little to no resistance at higher temperatures than before.
Spherical tokamaks, which resemble a cored apple rather than the doughnut-like shape of conventional tokamaks and are being investigated as a potential design for future fusion power plants, would more readily fit such massive magnets within the small space inside of them.
Researchers could fix the magnets without disassembling any other components since they could be placed apart from other equipment in the spherical tokamak’s central chamber to contain the heated plasma that powers fusion reactions.
“To do this, you need a magnet with a stronger magnetic field and a smaller size than current magnets,” said Yuhu Zhai, a principal engineer at PPPL and lead author of a paper reporting the results in IEEE Transactions on Applied Superconductivity. “The only way you do that is with superconducting wires, and that’s what we’ve done.”
When light elements are combined, they create plasma, a hot, charged state of matter made up of free electrons and atomic nuclei that produces enormous amounts of energy. Fusion is the process that powers the sun and stars.
In order to create a potentially limitless supply of secure and healthy energy to power electricity production, scientists are working to duplicate fusion on Earth. Compared to copper magnets, high-temperature superconducting magnets provide a number of advantages.
High-temperature superconducting magnets can help 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, enhancing operating conditions.Thomas Brown
They are better suitable for use in future fusion power plants that will need to run for months at a time since they can be turned on for longer periods of time than copper magnets can.
Additionally potent, superconducting wires may produce a greater magnetic field while transmitting the same amount of electrical current over a far broader path than a copper wire. The magnets might also assist researchers in their ongoing efforts to reduce the size of tokamaks, enhancing performance and lowering building costs.
“Tokamaks are sensitive to the conditions in their central regions, including the size of the central magnet, or solenoid, the shielding, 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 cost while, in theory, improving performance.”
These brand-new magnets benefit from a method developed by Zhai and scientists from Advanced Conductor Technologies, the University of Colorado Boulder, and the National High Magnetic Field Laboratory in Tallahassee, Florida.
By using this method, the wires can be electrically insulated without using traditional materials like epoxy and glass fiber. The method cuts expenses while streamlining construction.
“The costs to wind the coils are much lower because we don’t have to go through the expensive and error-prone epoxy vacuum-impregnation process,” Zhai said. “Instead, you’re directly winding the conductor into the coil form.”
Moreover, “high-temperature superconducting magnets can help 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, enhancing operating conditions,” said Thomas Brown, a PPPL engineer who contributed to the research.
“Also, the smaller, more powerful magnets give the machine designer more options to design a spherical tokamak with geometry that could enhance overall tokamak performance. We’re not quite there yet but we’re closer and maybe close enough.”
This research was supported by the U.S. Department of Energy (Small Business Innovation Research and Laboratory Directed Research and Development).