The performance characteristics of a small-scale experimental device are analyzed before experiments to study behavior of ions and electrons in the magnetic and electric fields, and to demonstrate the principle of the CUSPDEC; especially, the capability of separation of ions and electrons by designed magnetic field even under the self-induced electric field. Numerical experiments with a two-dimensional approximation give the following results: (1) The adequate current density is 500 A/cm2 and 300 A/cm2 for magnet coils, resulting in the magnetic flux density of 8.2 × 10–2 [T] at the center between the magnet coils. (2)The pitch angle of protons at the inlet must be less than about 20°.