Nucleation and pinning of continuous vortices in superfluid 3He-A

Using a rotating nuclear demagnetization cryostat, we studied flow-induced nucleation, pinning and annihilation of continuous vortices in superfluid He-3-A in zero magnetic field. Two disk-shaped slabs of 3 He-A of radius 5 mm and thicknesses 0.26 and 0.44 mm have been investigated. Critical velocities for vortex nucleation, v,, were measured both in uniform (I) over cap -textures and in textures with many domain walls of (I) over cap -vector Only after introducing multiple domain walls to the (I) over cap -texture, we observed strong pinning of vorticity. In this case, the hysteretic dependences of the trapped vorticity on the maximal angular velocity of rotation were found to be fairly universal for both slab thicknesses and different densities of domain walls. A phenomenological model of a critical state set by either the critical velocity for vortex nucleation or pinning strength is in good agreement, with all observations. (c) 2005 Elsevier Ltd. All rights reserved.