  The chromomagnetic vacuum of SU(2) gluodynamics is considered in the
background of a finite radius flux tube (center-vortex) with homogeneous field
inside and zero field outside. In this background there are tachyonic modes.
These modes cause an instability. It is assumed that the selfinteraction of
these modes stops the creation of gluons and that a condensate will be formed.
For constant condensates, the minimum of the effective potential is found on
the tree level. In the background of these condensates, all tachyonic modes
acquire nonzero, real masses which will result in a real effective potential of
this system.
  Considering only the tachyonic modes and adding the energy of the background
field, the total energy is found to have a minimum at some value of the
background field, which depends on the coupling of the initial SU(2) model. For
small coupling, this dependence is polynomial in distinction from the Savvidy
vacuum where it is exponentially suppressed. The minimum of this energy will
deepens with shrinking radius of the flux tube. It can be expected that this
process can be stopped by adding quantum effects. Using the high temperature
expansion of the effective potential, it can be expected that the symmetry,
which is broken by the condensate, will be restored at sufficiently high
temperature.
