  When a circularly-symmetric light beam with optical vortex (OV) diffracts at
an opaque screen with the sharp edge, the OV core is displaced from the beam
axis and, in case of the m-charged incident OV, decomposed into |m|
single-charged ones. By means of numerical simulations and based on examples of
incident beams with topological charges |m| =1, 2, 3 we show that, while the
screen edge monotonously advances towards the beam axis, the OVs in the
diffracted beam cross section move away from the incident beam axis along
spiral-like trajectories. The trajectories contain fine structure details that
reflect the nature and peculiar spatial configuration of the diffracting beam.
For the Kummer beams' diffraction, the trajectories contain self-crossings and
regions of "backward" rotation (loops); in case of Laguerre-Gaussian beams, the
trajectories are smoother. The numerical results are supported by analytical
approximations and conform with experiment The general shape of the
trajectories and their local behavior show high sensitivity to the diffraction
conditions (spatial structure of the diffracting beam, its disposition with
respect to the screen edge, etc.), which can be used in diverse metrological
applications.
