Time-of-Flight Experiments of Vortex Rings Propagating from Turbulent Region of Superfluid 4 He at High Temperature
We report the time-of-flight of quantized vortex rings generated by a vibrating wire in superfluid 4He which contains normal fluid component. A cover box of vibrating wires and slow cooling of superfluid reduce the number
of vortices attached to wire surfaces, enabling us to study vortex rings propagating from a turbulent region. Using two vibrating
wires as a generator and a detector of vortices, the time-of-flight of vortices propagating a distance of 0.88 mm was measured
at 1.25 K. We find that the time-of-flights distribute from 0.06 s to 27.4 s, much larger than the lifetimes of circular vortex
rings limited in the size of a generator amplitude. These results imply that large vortex rings with non-circular shape or
vortex tangles are created by the generator, propagating slowly and colliding with the detector before complete disappearance.