Experimental investigation of the circulation and the propagation of macroscopic ring vortices in He 2

Normal fluid and superfluid vorticity, produced by forcing helium 2 out of a tube 8 mm in inner diameter at velocities of about 10 cm/sec, was investigated in the region in front of the tube orifice. The method of circulation measurement was based on the flow induced variation in the running times of second sound shock waves. The formation of large scale vortex rings, which moved downstream along their axis of symmetry, was observed and measured. Close to the orifice, the normal fluid circulation decreases with decreasing temperature, nearly vanishing at the lowest temperature under consideration, and changes during the translational motion of the vortex rings.