  We consider the effect of the magnetic field background in the form of a tube
of the finite transverse size on the vacuum of the quantized charged massive
scalar field which is subject to the Dirichlet boundary condition at the tube.
It is shown that, if the Compton wavelength associated with the scalar field
exceeds considerably the transverse size of the tube, then the vacuum energy
which is finite and periodic in the value of the magnetic flux enclosed in the
tube is induced on a plane transverse to the tube. Some consequences for
generic features of the vacuum polarization in the cosmic-string background are
discussed.
