Probability current tornado loops in three-dimensional scattering

We consider scattering of a three-dimensional particle on a finite family of delta potentials. For some parameter values the scattering wavefunctions exhibit nodal lines in the form of closed loops, which may touch but do not entangle. The corresponding probability current forms vortical singularities around these lines; if the scattered particle is charged, this gives rise to magnetic flux loops in the vicinity of the nodal lines. The conclusions extend to scattering on hard obstacles or smooth potentials. (C) 1998 Elsevier Science B.V.