Additive-Manufactured and Topology-Optimized Permanent-Magnet Spin Rotator for Neutron Interferometry

In neutron-interferometric experiments using polarized neutrons, coherent spin-rotation control is indispensable. In this article, we present a method for Larmor spin rotation around an axis parallel to the outer guide field using topology-optimized three-dimensional (3D) printed magnets. The use of 3D-printed magnets instead of magnetic coils avoids unwanted inductances and offers the advantage of no heat dissipation, which prevents potential loss in interferometric contrast (fringe visibility) due to temperature gradients in the interferometer. We use topology optimization to arrive at a design of the magnet geometry that is optimized for homogeneity of the magnetic action over the neutron-beam profile and adjustability by varying the distance between the 3D-printed magnets. We verify the performance in polarimetric and interferometric neutron experiments.