  Confinement in QCD is caused by vacuum fluctuations of gluon fields. There
are two numerically different scales, characterizing nonperturbative QCD vacuum
dynamics: a "small" scale, corresponding to gluon condensate, critical
temperature etc, which is about 0.2-0.3 GeV, and a "large" one, given by
inverse confining string width, glueball and gluelump masses etc, which is
about 1.5-2.5 GeV. We discuss this mismatch in a picture where confinement is
ensured by two-point gauge-invariant field strength correlator of special type.
It supports most of perturbative and nonperturbative dynamics, while
contribution of other terms is argued to be small. This object, on the other
hand, can be expressed via gluelump Green's function, whose dynamics is defined
in terms of the same correlator. In this way one obtains a self-consistent
scheme of mean-field type leading to permanent confinement at temperatures less
than the critical one.
