  We develop here a nonperturbative framework to study quantum chromodynamics
(QCD) at finite temperatures using the thermofield dynamics (TFD) method of
Umezawa. The methodology considered here is self-consistent and variational.
There is a dynamical generation of a magnetic gluon mass. This eliminates the
infrared problems associated with perturbative QCD calculations at finite
temperatures. We obtain here the thermodynamical quantities like free energy
density, pressure and entropy density. We also calculate the temperature
dependence of SVZ parameter ${\alpha_{s} \over \pi}<{G^a}_{\mu \nu } {G^{a \mu
\nu }}>$. The condensate vanishes at the critical temperature in accordance
with recent hot sum rule calculations. The present method gives an insight to
the vacuum structure in QCD at zero temperature as well as at finite
temperatures in a co-ordinated manner. (to appear in Z. Physik C )
