fusion energy reactor

Permanent magnets could finally bring fusion energy to life

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Fusion energy could be developed faster with the use of permanent magnets, according to researchers from Princeton Plasma Physics Laboratory (PPPL).

Permanent magnets can greatly simplify the design and production of fusion facilities, called stellarators, which are comprised of 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 believe, allowing simple, non-twisted coils to produce the remaining part in place of the complex coils.

“The twisted coils are the most expensive and complicated part of the stellarator and have to be manufactured to very great precision in a very complicated form,” said Per Helander, lead author on the research. “We are trying to ease the requirement on the coils by using permanent magnets.”

The researchers said that simpler stellarators based on permanent magnets do not run the risk of damaging disruptions that more widely used tokamak fusion devices face.

Fusion is the process that allows the Sun to function, combining light elements in the form of plasma that generates massive amounts of energy.

Scientists around the world are using tokamaks, stellarators and other facilities in an effort to create and control fusion on Earth for a virtually inexhaustible supply of safe and clean power to generate electricity.

The team plans to use rare-earth magnets which are capable of generating “quite powerful” fields for the magnets’ small size.

These are 'hard' fields that are almost unaffected by other fields nearby and can therefore provide what physicists call the 'poloidal' part of a spiralling stellarator field. 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 - a current that requires power supplies, which permanent magnets do not need.

They are also lower cost than hand-crafted electromagnets and are easily repositioned to create a variety of shapes for the magnetic fields.

They do have disadvantages, such as the inability to turn them off and their limited maximum field strength, but it is hoped that stronger permanent magnets may become available in due course.

The researchers plan to build a table-top stellarator with permanent magnets installed before constructing a larger, optimised stellarator that can meet specific performance goals.

That facility could be upgraded to increase its field strength, in preparation for continued development of the simplified machine.

Last week, a team demonstrated how to produce permanent magnets with a lower environmental impact than is currently possible.


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