  Inelastic electron scattering is applied to investigate the impact of
potassium intercalation on the charge carrier plasmon energy and dispersion in
the charge-density wave (CDW) bearing compound 2H-tantalum-diselenide. We
observe an unususal doping dependence of the plasmon dispersion, which even
changes sign upon alkali addition. In contrast to the continous energy shift of
the plasmon position upon doping at lowest momentum transfer, its dispersion
changes in a rather discontinuous manner. We argue that the observed dynamics
can only be explained in a picture, where complex phenomena are taken into
account including the suppression of the CDW upon doping as well as the
interplay of the CDW and the plasma resonance.
