Stellarator Fields without Stellarator Coils: MUSE a table top PM stellarator

MUSE is a table-top permanent magnet (PM) stellarator that uses simple circular coils, together with a PM array, to produce a stellarator vacuum equilibrium. The plasma configuration (R = 30 cm, B = 1.5 kG) is optimized to be quasi-axisymmetric. We found that our PM array produces free boundary VMEC equilibria with neoclassical transport metrics a factor of 10-100 better than that of any constructed device. This might be due to the larger degrees of freedom available to PM compared to modular coils. From an engineering perspective, our PM array is composed of simple, identical magnets with equal magnetization all polarized axially. This simplifies assembly and procurement, but finding such a uniform distribution poses significant challenges for continuous optimization. We will discuss discrete optimization methods used to address these challenges. We also examine sensitivity of the PM array to assembly displacements and material irregularity. The extension of these methods to larger devices is also discussed.