“Double-well” potential structure (virtual cathode formation) is studied in a spherical inertial electrostatic confinement (SIEC) device using non-linear Poisson's equation. Particle densities are derived from a kinetic equation equivalent to Vlasov's equation. Velocities of collision-free electrons and ions at the edge of the configuration will be almost aligned towards the center, however, they have small divergences. Analyses show appearance of a virtual cathode potential well relevant to bum fusion fuels near the center of SIEC.