  This paper is concerned with multidimensional Euler-Poisson equations for
plasmas. The equations take the form of Euler equations for the conservation
laws of the mass density and current density for charge-carriers (electrons and
ions), coupled to a Poisson equation for the electrostatic potential. We study
the limit to zero of some physical parameters which arise in the scaled
Euler-Poisson equations, more precisely, which is the limit of vanishing ratio
of the electron mass to the ion mass. When the initial data are small in
critical Besov spaces, by virtue of the ``Shizuta-Kawashima" skew-symmetry
condition, we establish the uniform global existence and uniqueness of
classical solutions. Then we develop new frequency-localization Strichartz-type
estimates for the equation of acoustics (a modified wave equation) with the aid
of the detailed analysis of the semigroup formulation generated by this
modified wave operator. Finally, it is shown that the uniform classical
solutions converge towards that of the incompressible Euler equations (for
\textit{ill-prepared} initial data) in a refined way as the scaled
electron-mass tends to zero.
