Vortex nucleation by a moving ion in a Bose condensate

The nonlinear Schrodinger equation is used to analyze the superfluid flow a round an ion and to elucidate the vortex nucleation process. Asymptotic exp ansion for the flow is used to find the critical velocity of the ion for vo rtex production. 3D numerical calculations demonstrate, that if the axisymm etry of the flow is broken by introducing a solid boundary several healing length from the sphere, vortex loops rather than vortex rings may be formed . These loops may detach from the ion and attach themselves to the wall. In the presence of small 3D random noise, the system still favors the creatio n of vortex rings. (C) 2000 Elsevier Science B.V. All rights reserved.