  Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and
they naturally tend to relax into lower energy states by developing
instabilities or by diffusion. But the actual amount of energy in such
inhomogeneities has remained unknown. In the present work the amount of energy
stored in a density gradient is calculated for several specific density
profiles in a cylindric configuration. This is of practical importance for
drift wave instability in various plasmas, and in particular in its application
in models dealing with the heating of solar corona because the instability is
accompanied with stochastic heating, so the energy contained in inhomogeneity
is effectively transformed into heat. It is shown that even for a rather
moderate increase of the density at the axis in magnetic structures in the
corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored
in such a density gradient becomes several orders of magnitude greater than the
amount of total energy losses per unit volume (per second) in quiet regions in
the corona. Consequently, within the life-time of a magnetic structure such
energy losses can easily be compensated by the stochastic drift wave heating.
