Simulation experiments of traveling wave direct energy converter (TWDEC) on GAMMA 10 tandem mirror have been performed. Following to initial experiments reported previously, full biasing system including measurement system has been constructed. The biasing system has successfully worked showing that energy distribution is shifted corresponding to the bias voltage. Examination of approximated energy distribution functions reveals that the deceleration effect by TWDEC operation is found for an appropriate relative phase difference between modulator and decelerator RFs.