A direct energy conversion system designed for D-3He fusion reactor consists of a CUSP direct energy converter (DEC) and a Traveling Wave DEC, where, respectively, electrons and thermal ions are separated from fusion protons and decelerated via Venetian blind type electrodes to produce DC power, and protons are velocity-modulated, bunched, and then decelerated by RF traveling waves to produce RF power. For the basic investigation of the CUSPDEC, a small scale experiment is conducted using a device consisting of a single cusp and low-energy plasma and ion sources. Performed are the measurements of basic characteristics of the behavior of charged particles in various conditions including magnetic field gradients, spatial locations of incidence, ion masses, and ion energies.