Are Permanent Magnets the Solution For Delivering Fusion Energy?

According to research published in the journal Physical Review Letters, permanent magnets akin to those used on refrigerators could speed the development of fusion energy. Phys.Org reports: In principle, such magnets can greatly simplify the design and production of twisty fusion facilities called stellarators, according to scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) and the Max Planck Institute for Plasma Physics in Greifswald, Germany. PPPL founder Lyman Spitzer Jr. invented the stellarator in the early 1950s. Most stellarators use a set of complex twisted coils that spiral like stripes on a candy cane to produce magnetic fields that shape and control the plasma that fuels fusion reactions. Refrigerator-like permanent magnets could produce the hard part of these essential fields, the researchers say, allowing simple, non-twisted coils to produce the remaining part in place of the complex coils.

Rare earth magnets have surprising and useful properties. They generate quite powerful fields for the magnets' small size, and these are "hard" fields that are almost unaffected by other fields nearby. These magnets could thus provide what physicists call the "poloidal" part of a spiraling stellarator field, while simple round coils could provide the "toroidal" part that makes up the rest of the field. Permanent magnets are always "on" in sharp contrast to the standard electromagnetic coils that stellarators and tokamaks use. Such coils create magnetic fields when an electric current runs through them -- current that requires power supplies that permanent magnets do not need. Other advantages of the use of permanent magnets to simplify stellarator coils include: Lower cost than hand-crafted electromagnets; Creation of ample space between the simplified coils to facilitate maintenance; Ability to reposition the magnets to create a variety of shapes for the magnetic fields; and Reduced engineering and manufacturing risks. Permanent magnets have disadvantages, too. "You can't turn them off," physicist Per Helander said, which means they can pull in anything they can attract within range. They also produce limited maximum field strength, he said. Nonetheless, such magnets "can be great for creating experiments on the way to a reactor," he added, "and stronger permanent magnets may become available."

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