Ion-flux-dependent nanoparticle formation is observed in silica glasses during high-flux 60 keV Cu- implantation. Under the high-flux implantation, a strong electric field possibly forms in the glasses, and may affect the nanoparticle formation via the solute diffusion processes. In this study, the internal-field formation is evaluated based on a model of negative-ion implantation, in which the difference in diffusion lengths between electrons and holes induces field formation. The calculated fields remain at more than 2000 nm in depth, although the ion range is ∼45 nm. The fields depend negligibly on the ion flux and the maximum value is 3.3 kV/cm. A mechanism for creating the internal field and the possibility of high-flux effects are discussed.