Superfluid He in Rotation: Single-Vortex Resolution and Requirements on Rotation

The present generation of rotating refrigerators, which are used for the study of quantized vorticity in helium superfluids, are often capable of cooling to mK temperatures and rotate up to ’ 1 rev/s. To achieve single-vortex resolution at all rotation velocities, smooth and stable rotation is required. This calls for low and stable rotational friction, sufficient axial alignment and lateral balancing of weights, to promote mechanical stability and precessionfree rotation. We comment on general design principles, discuss the rotation noise spectrum of our installation, and describe interference problems from the rotation in low-noise measurement.