  We study novel type of contributions to the partition function of the Maxwell
system defined on a small compact manifold ${\mathbb{M}}$ such as torus. These
new terms can not be described in terms of the physical propagating photons
with two transverse polarizations. Rather, these novel contributions emerge as
a result of tunnelling events when transitions occur between topologically
different but physically identical vacuum winding states. These new terms give
an extra contribution to the Casimir pressure, yet to be measured.
  We argue that if the same system is considered in the background of a small
external time-dependent magnetic field, than there will be emission of photons
from the vacuum, similar to the Dynamical Casimir Effect (DCE) when real
particles are radiated from the vacuum due to the time-dependent boundary
conditions. The difference with conventional DCE is that the dynamics of the
vacuum in our system is not related to the fluctuations of the conventional
degrees of freedom, the virtual photons. Rather, the radiation in our case
occurs as a result of tunnelling events between topologically different but
physically identical $|k>$ sectors in a time -dependent background. We comment
on relation of this novel effect with the well-known, experimentally observed,
and theoretically understood phenomena of the persistent currents in normal
metal rings. We also comment on possible cosmological applications of this
effect.
