  We present a study of the possible plasmon excitations that can occur in
systems where strong superconductivity is present. In these systems the plasmon
energy is comparable to, or smaller than the pairing gap. As a prototype of
these systems we consider the proton component of neutron star matter just
below the crust when electron screening is not taken into account. For the
realistic case we consider in detail the different aspects of the elementary
excitations when the proton, electron components are considered within the
Random Phase Approximation generalized to the superfluid case, while the
influence of the neutron component is considered only at qualitative level.
Electron screening plays a major role in modifying the proton spectrum and
spectral function. At the same time the electron plasmon is strongly modified
and damped by the indirect coupling with the superfluid proton component, even
at moderately low values of the gap. The excitation spectrum shows the
interplay of the different components and their relevance for each excitation
mode. The results are relevant for neutrino physics and thermodynamical
processes in neutron stars. If electron screening is neglected, the spectral
properties of the proton component show some resemblance with the physical
situation in high T$_c$ superconductors, and we briefly discuss similarities
and differences in this connection. In a general prospect, the results of the
study emphasize the role of Coulomb interaction in strong superconductors.
