Vortex line density of superfluid suction vortex

Although a suction vortex is one of the most common vortices appearing in everyday life, its internal structure has not been fully understood yet. We experimentally generate directly a superfluid suction vortex with a superfluid stirring system. A quantum vortex line carries all the microscopic circulation, and the distribution of vortex lines can be measured by combining two acoustic techniques. The results show that the vortex lines accumulate in the narrow region around the axis of symmetry. However, the vortex lines are not a simple bundle of straight vertical lines, but most of them incline in the horizontal direction.