  We consider the zero-electron-mass limit for the Navier-Stokes-Poisson system
in unbounded spatial domains. Assuming smallness of the viscosity coefficient
and ill-prepared initial data, we show that the asymptotic limit is represented
by the incompressible Navier-Stokes system, with a Brinkman damping, in the
case when viscosity is proportional to the electron-mass, and by the
incompressible Euler system provided the viscosity is dominated by the electron
mass. The proof is based on the RAGE theorem and dispersive estimates for
acoustic waves, and on the concept of suitable weak solutions for the
compressible Navier-Stokes system.
