Observation of Second Sound Attenuation Across a Superfluid Suction Vortex

Recently, the authors succeeded in generating a superfluid suction vortex, which is a giant vortex with a hollow core, driven directly by a cryogenic centrifugal pump. The ultimate goal of this study and related work is to determine the distribution of the local density of the quantum vortex lines as a function of the rotational speed and the magnitude of the suction flow. Although the flow of superfluid helium in a rotating bucket, in which the vortex lines are arranged to form a triangular lattice, is known to show rigid body motion, the vortex line distribution of the suction vortex remains an open question. In this study, the attenuation of the second sound across the suction vortex was measured. As a result, it was found that the damping factors of the second sound increased with increasing rotational speed; however, it was found that the apparent vortex line density is not proportional to the rotational speed despite the fact that the total circulation has been previously shown to be proportional to the rotational speed. A possible picture of the quantum vortex lines around the suction vortex is discussed in this paper.