COLLECTIVE MOTION OF QUANTIZED VORTEX LINES IN ROTATING SUPERFLUID 3HE-B

Insight in the dynamics of quantized vortex lines has been obtained by performing NMR measurements in uniformly rotating superfluid He-3-B. Compared to superfluid He-4, in He-3-B the viscosity of the normal com ponent is three orders of magnitude larger and the pinning of vortices is weaker. The collective modes governing the hydrodynamic response o f an array of vortex lines are highly overdamped. Two distinct modes a re identified: (1) a relatively fast mutual-friction-resisted mode, wh ich controls the redistribution of the vortex density on a time scale of a few seconds, and (2) an exponentially relaxing slow mode with a t ime constant of a few minutes, which governs asymptotically the approa ch to equilibrium at nearly constant vortex density. Measurement of th e fast motion allows us to extract the dissipative mutual friction. Th e slow mode is dominated by the elastic tension along the vortex line and by weak pinning at the top and bottom surfaces of the rotating con tainer. With increasing vortex density the surface pinning becomes a c ollective process, in which coherently moving groups of vortices are p inned in unison. Collective pinning is a result of the shear elasticit y related to the crystalline order of the vortex lattice. Our measurem ents on the slow mode indicate that the crystalline correlation extend s over many lattice spacings.