MUSE: The World's First Permanent Magnet Stellarator

Thursday - May 9 2024, 08:36 UTC - 1 year ago

MUSE is the world's first permanent magnet stellarator, which uses commercially available magnets and 3D-printed parts to reduce costs by 100 times. It has a unique quasi-axisymmetric design and has the potential to revolutionize the way optimized stellarators are built. Experiments are now underway.

In the world of experimental physics and nuclear fusion, the cost of building devices for research and testing can be astronomical. However, a team at the Princeton Plasma Physics Laboratory (PPPL) has found a way to make these devices 100 times cheaper by using a combination of nuclear processes and permanent magnets.Stellarators, which are devices used in experimental physics and nuclear fusion tests, typically rely on complicated electromagnets that have complex shapes and create their magnetic fields through the flow of electricity .

These electromagnets must be built precisely with very little room for error, increasing their cost. However, permanent magnets, like the magnets that hold art to refrigerator doors, do not need electric currents to create their fields. They can also be ordered off the shelf from industrial suppliers and then embedded in a 3D-printed shell around the device’s vacuum vessel, which holds the plasma .

The team at PPPL purchased more than 10,000 magnets at commercially available specifications, with tolerances of 5% on magnetisation magnitude, 3∘ on magnetisation orientation, and 1 mm on physical dimensions. They also used multi-jet fusion 3D-printing technology to fabricate the permanent magnet holders using nylon plastic. By doing so, they were able to construct the world's first permanent magnet (PM) stellarator, named MUSE .

But the construction of MUSE was not just about using commercially available parts and 3D-printing technology. The team also developed a PM optimisation algorithm to pack the dipoles densely and minimize surface field error, while also ensuring the PM constraints were met. This algorithm, called FAMUS, treats the PM system as a set of ideal point dipoles. From there, the team constructed finite-volume magnet towers to be housed in the 3D-printed PM holders .

The design of these PM holders was validated by laser metrology to ensure precision.One of the challenges in building a device like MUSE is accounting for finite permeability and sensitivity to perturbations. The team found that these effects can be compensated for by slightly adjusting the TF coil current. They also analyzed the magnetostatic forces between the PM holders and used an exact analytic formula to compute the forces and stress on the holders .

With construction complete, MUSE is now ready for experiments. It is the first quasi-axisymmetric experiment, meaning it has symmetry about its vertical axis but not its horizontal axis. This unique design has the potential to revolutionize the way optimized stellarators are built, making them 100 times cheaper than traditional methods. And with present materials, the poloidal field produced by an individual PM in MUSE is less than 1 Tesla, demonstrating the effectiveness of this new approach .

In conclusion, the MUSE project has successfully demonstrated the use of permanent magnets in constructing a stellarator for experimental physics and nuclear fusion tests. By utilizing commercially available parts and advanced 3D-printing technology, MUSE has the potential to significantly reduce the cost of building these types of devices. With experiments now underway, the team at PPPL is excited to see the results and the impact that MUSE will have on the world of experimental physics and nuclear fusion .