We investigate a new version of the flux-tube model based on joint action of two different processes responsible for vacuum creation of the parton plasma: the dynamical Schwinger mechanism and the geometrical mechanism linked to the dynamical Casimir effect. These two mechanisms act at different time scales. The Casimir mechanism provides the abundant generation of partons from the sea at the very early stage after the fusion of colliding nuclei and release of color degrees of freedom. Then the created plasma initiates the backreaction mechanism via the standard Schwinger scenario. This process apparently leads to fast thermalization of secondary partons. The model allows for the self-consistent description of preequilibrium evolution of the plasma, fully determined by the total energy and the total number of valence quarks of colliding nuclei. The Equation of State of the created parton plasma is discussed.