Superfluid Suction Vortex Generated by Fountain Effect

In viscous fluids, it is believed that a suction vortex is stable because the diffusion of the vorticity due to viscosity and the vorticity confinement due to flow toward the center are balanced. Therefore, the question of whether suction vortices are stable even in superfluidity is of academic importance. We have generated suction vortices by rotating turbines directly in low-temperature helium. However, this method has several problems; the suction flow could not be determined quantitatively, and we could not stabilize the motion of the turbine at low rotation speeds. In this study, we overcame these problems by introducing a pump using a fountain effect. The first step in this experiment was to determine the performance of the pump. Next, we applied this pump as a circulating pump for suction vortex generation. The vortex thus generated had perfect rotational symmetry as derived from elementary hydrodynamic equations, and its shape was stable in time. Therefore, we have succeeded for the first time in determining the rotational velocity field and circulation from the shape of the vortex generated by the fountain effect.