  We investigate fundamental processes that govern dynamics of vortex
nucleation in sub-100 nm mesoscopic magnets. We focus on a structure with
broken symmetry - Pacman-like nanomagnet shape - in which we study
micromagnetic behavior both by means of a simple model and numerically. We show
that it is possible to establish desired vortex chirality and polarity by
applying only quasi-static in-plane magnetic field along specific directions.
We identify the modes of vortex nucleation that are very robust against
external magnetic field noise. These vortex nucleation modes are common among
wide range of sub-100 nm magnets with broken rotational symmetry.
