DOE lab develops possible fusion magnet

Scientists at the United States Department of Energy Princeton Plasma Physics Laboratory (PPPL) have designed a new type of magnet made from niobium and tin that could aid devices ranging from tokamaks to x-ray machines.

In a recent experiment that shattered its old record, researchers at the Joint European Torus (JET) facility reported producing 59 megajoules of energy over five seconds with the holy grail of energy, fusion – more than doubling the facility's previous record of 21.7 megajoules in 1997.

To accomplish this feat, a magnetic ring-shaped or doughnut-shaped chamber known as a tokamak was used, creating a type of magnetic confinement space in which hot gas or plasma is controlled within the chamber.

You can read about the complete achievement at Scientists break fusion power record in the February 23, 2022, edition of Metal Tech News.

Tokamaks rely on a central electromagnet called a solenoid to create electrical currents and magnetic fields that confine the plasma so fusion reactions can occur. But after being exposed over time to energetic subatomic particles, the insulation surrounding the electromagnet's wires degrade.

If they do, the magnet could fail, thus reducing the tokamak's ability to harness fusion power.

With the recently designed magnet, metal acts as insulation, and therefore the possibility of the magnet being damaged is, theoretically, significantly reduced. Additionally, beyond the degradation of the surrounding insulation, the magnet itself heats up and becomes unstable; with this new magnet, it is purported to be capable of operating at higher temperatures than current superconducting electromagnets.

"Our innovation both simplifies the fabrication process and makes the magnet more tolerant of the radiation produced by the fusion reactions," said Yuhu Zhai, a principal engineer at PPPL and lead author of the paper detailing the results.

"If we are designing a power plant that will run continuously for hours or days, then we can't use current magnets," added Zhai. "Those facilities will produce more high-energy particles than current experimental facilities do. The magnets in production today would not last long enough for future facilities like commercial fusion power plants."

Electromagnets differ from everyday magnets like those used to keep your fridge door closed. Consisting of a coil of insulated wire carrying an electrical current that generates a field as it flows, electromagnets are used in a variety of devices such as cranes in junkyards to magnetic-resonance imaging (MRI) devices that take full-body scans of your insides.

Zhai and colleagues have managed to build a prototype, which has recorded encouraging results.

"During our tests, our magnet produces about 83% of the maximum amount of electrical current the wires can carry, a very good amount," said Zhai. "Scientists typically only use 70% of the superconducting wire electrical current capacity when designing and building high-power magnets. And large-scale magnets like those in ITER (Interior Joint European Torus), the international fusion facility being constructed in France, often use only 50%."

The new magnet has wires constructed out of the elements niobium and tin, and when heated in a particular way, these alloy to form a superconductor that allows electrical current to flow through it at extremely low temperatures with no resistance – meaning there is much less need for insulation to prevent current leakage.

"This new concept is interesting because it allows the magnet to carry a lot of electrical current in a little space, reducing the amount of volume the magnet occupies in a tokamak," said PPPL Chief Engineer Robert Ellis. "This magnet could also operate at higher current densities and stronger magnetic fields than magnets can today. Both qualities are important and could lead to lower costs."

Overall, the new development could profoundly benefit the development of fusion energy, a dream of humanity since it began exploring the infinitesimally small universe of particles.

"This is a revolutionary change in how you make electromagnets," said Michael Zarnstorff, PPPL's chief science officer. "By creating a magnet with just metal and removing the need to use insulation, you get rid of a lot of the costly steps and reduce the number of opportunities for the coil to malfunction. This is really important stuff."

Zhai and collaborators around the country and the world are now working with private industry to further develop an insulation-free prototype. This new type of high-temperature superconductor-based electromagnet could be a foundational component of a pilot fusion power plant and be the next vital piece to the puzzle of unlimited clean energy.