  Wightman function, the vacuum expectation values of the field square and the
energy-momentum tensor are investigated for a massive scalar field with general
curvature coupling parameter in the region between two coaxial cylindrical
boundaries. It is assumed that the field obeys general Robin boundary
conditions on bounding surfaces. The application of a variant of the
generalized Abel-Plana formula allows to extract from the expectation values
the contribution from single shells and to present the interference part in
terms of exponentially convergent integrals. The vacuum forces acting on the
boundaries are presented as the sum of self-action and interaction terms. The
first one contains well-known surface divergences and needs a further
renormalization. The interaction forces between the cylindrical boundaries are
finite and are attractive for special cases of Dirichlet and Neumann scalars.
For the general Robin case the interaction forces can be both attractive or
repulsive depending on the coefficients in the boundary conditions. The total
Casimir energy is evaluated by using the zeta function regularization
technique. It is shown that it contains a part which is located on bounding
surfaces. The formula for the interference part of the surface energy is
derived and the energy balance is discussed.
