I have been writing about nuclear fusion lately. A great deal of current research is being conducted with tokamaks which are donut shaped cavities surrounded by superconducting electromagnets to heat, compress, and confine a hydrogen plasma. A stellarator was an early design concept in which the cavity was twisted from the tokamak donut configuration to more of a figure eight. This helped confine the plasma through magnetic field geometry. Although the stellarator was invented in 1951, problems with plasma confinement and heating have discouraged the idea of trying to build a commercial fusion reactor according to that design for many years.
Michael Zarnstorff at the Max Planck-Princeton Research Center for Plasma Physics and three other researchers are working on a new concept for stellarators that is based on the use of permanent magnets instead of electromagnets. In a new paper about their work, he said, “It is shown that the magnetic-field coils of a stellarator can, at least in principle, be substantially simplified by the use of permanent magnets.”
In a permanent magnet, the magnetic field is caused by the chemical elements involved as well as the arrangement of domains in the material. In an electromagnetic, the magnetic field is a result of passing an electric current through a metal coil. Permanent magnets cannot generate the necessary plasma flux in a stellarator. Zarnstorff says that they have other ways of shaping the flux of the plasma to control it.
The stability of a tokamak or stellarator in dependent on careful management of the shape and strength of the magnetic field inside. Extremely hot moving plasma has a very corrosive effect on any containment vessel. The process of corrosion can reduce the temperature of the plasma and move it out of the energy producing zone. This is the part of the stellarator design that can be improved by permanent magnetics.
Permanent magnets cannot be used to generate the entire magnetic field necessary for the stellarator. However, they can supplement the field generated by the electromagnetics and add necessary structure to the field. The repost says, “Such magnets cannot produce toroidal magnetic flux, but they can create poloidal flux and rotational transform of the magnetic field, and thus help to simplify stellarator design.”
“In the original design, the magnetic field was created by 20 nonplanar, modular coils of 5 different types. Leaving permanent magnets to do most of the plasma shaping, a new optimization was now carried out where only 8 identical, planar, circular toroidal-field coils proved necessary.”
Permanent magnets are fixed solids and do not require any special equipment or injection of energy. When they are used to replace complicated electromagnetic coils in stellarators it makes design and construction simpler. In addition, it is easier to generate and maintain the high temperature needed in the plasma.
Tokamaks and stellarators are just two of the designs being explored for the creation of a nuclear fusion reactor. Other designs fire lasers into a hydrogen pellet. A company in Seattle Washington is working on a system that uses powerful electromagnets to squeeze a magnetic field around a cloud of deuterium and helium-3 to send out pulses of electricity. There are at least a half-dozen different approaches to nuclear fusion being developed for commercial nuclear fusion by startups around the U.S. Time will tell if any of them can be the basis of electricity generated by the fusion process.