Design and construction of the MUSE permanent magnet stellarator

• Published in: Journal of plasma physics Vol. 89; no. 5
• Main Authors: Qian, T.M., Chu, X., Pagano, C., Patch, D., Zarnstorff, M.C., Berlinger, B., Bishop, D., Chambliss, A., Haque, M., Seidita, D., Zhu, C.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 31.10.2023
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Algorithms; Design; Dipoles; Equilibrium; fusion plasma; Geometry; Magnetic fields; Optimization; Permanent magnets; Perturbation; Plasma; plasma confinement; plasma devices; Plasma physics; Stellarators; The 23rd International Stellarator-Heliotron Workshop (ISHW); Three dimensional printing; plasma confinement; fusion plasma; plasma devices
• ISSN: 0022-3778; 1469-7807; 1469-7807
• DOI: 10.1017/S0022377823000880

This paper documents the design and construction of MUSE, the world's first permanent magnet (PM) stellarator and the first quasi-axisymmetric experiment. The purpose of MUSE is to develop and assess a new way of building optimised stellarators that uses simple planar coils PMs. Our PM optimisation algorithm consists of initialising a geometry to pack dipoles densely, running the FAMUS code to minimise surface field error subject to PM constraints and applying discrete jumps to reach a physically realisable solution. FAMUS treats the PM system as a set of ideal point dipoles. From there we construct finite-volume magnet towers to be housed in 3D-printed PM holders. We describe the design of the PM holders, which were validated by laser metrology. We analyse the effects of finite permeability, sensitivity to perturbations and magnetostatic forces. An exact analytic formula for the magnetic field from a finite-volume PM tower is presented to compute PM–PM forces and stress on the PM holder. Stellarator construction is complete and experiments are underway.