A nuclear fusion experiment at the University of Wisconsin-Madison has set a record for the strongest stable magnetic field to confine plasma, raising new hopes that future demonstration reactors will keep their promise to produce more power than they consume.
The new magnet comes from Commonwealth Fusion Systems (CFS), a pioneering fusion startup that provided the device for the WHAM experiment at UW-Madison earlier this month. When the WHAM team cooled the magnet to operating temperature and applied a strong current, the high-temperature superconductor generated a magnetic field of 17 Tesla—more than twice as strong as the high-resolution MRI scanners used to image the human brain.
Strong magnets are essential to the type of fusion power that CFS and others are pursuing. Every time the strength of the magnetic field doubles, the power output of a single reactor design increases by a factor of 16.
While WHAM has been operating for several years, “this is the first plasma using the new magnet,” said Kieran Furlong, co-founder and CEO of Realta Fusion. Realta split off from WHAM in 2022, but still works closely with UW-Madison scientists and the experiment itself.
The previous record was held by MIT's experimental reactor, the Alcator C-Mod, Furlong said.
WHAM's record-breaking magnetic field is a perfect example of how tightly coupled the fusion industry is. Research on the Alcator C-Mod helped prove the physics that underpins CFS's reactor and magnet designs.
CFS, spun out of MIT in 2018, is commercializing fusion power using a groundbreaking magnetic design. Both CFS and Realta are working to deploy reactors that use powerful magnetic fields to hold burning plasma in place so that hydrogen nuclei can fuse. The process releases a tremendous amount of heat. CFS’s reactor is known as a tokamak, which forces the plasma into a doughnut shape.
Meanwhile, Realta and WHAM are working on a magnetic mirror design, where two powerful magnets are spaced slightly apart to create a magnetic field that holds the plasma in a Tootsie-like shape. The magnets compress the plasma at both ends, and hydrogen ions bounce back and forth across the fat portion of the roll, colliding and fusing, releasing heat.
WHAM will serve as a testbed for mirror reactor designs. Once fully understood, Realta will build a demonstration reactor called Anvil, which it expects to complete in 10 years. Similar to WHAM but larger, it will provide more data for reactor design, as well as a way for scientists and engineers to test how different materials behave inside a working reactor.
Following Anvil, Realta plans to build Hammer, an evolutionary design with two magnets at each end instead of one. This will allow for a longer reactor, which will hopefully provide more power.
