  Inspired by the center-vortex dominance in the infrared sector of $SU(N)$
Yang-Mills theory observed on the lattice, we propose a vacuum wave functional
localized on an ensemble of correlated center vortices endowed with stiffness
and magnetic monopoles that change the orientation of the vortex flux. In the
electric-field representation, this wave functional becomes an effective
partition function for N complex scalar fields. The inclusion of both oriented
and non-oriented vortices as well as so-called N-vortex matchings leads to an
effective potential that has only a center symmetry left. In the center-vortex
condensed phase, this symmetry is spontaneously broken. In this case, the
Wilson loop average can be approximated by a solitonic saddle-point localized
around the minimal surface. The asymptotic string tension thus obtained
displays Casimir scaling.
