  The stability of two-dimensional bright vortex solitons in a media with
focusing cubic and defocusing quintic nonlinearities is investigated
analytically and numerically. It is proved that above some critical beam powers
not only one- and two-charged but also multiple-charged stable vortex solitons
do exist. A vortex soliton occurs robust with respect to symmetry-breaking
modulational instability in the self-defocusing regime provided that its radial
profile becomes flattened, so that a self-trapped wave beam gets a pronounced
surface. It is demonstrated that the dynamics of a slightly perturbed stable
vortex soliton resembles an oscillation of a liquid stream having a surface
tension. Using the idea of sustaining effective surface tension for spatial
vortex soliton in a media with competing nonlinearities the explanation of a
suppression of the modulational instability is proposed.
