In recent researches, an assisted glow discharge experiment using an external ion source has been tried to reduce operation gas pressure. As results, operating gas pressure has been successfully reduced from 1.5 Pa to 0.3 Pa, and the neutron production rate has increased.

These results are considered to be due to an increase of ion energy. However, it is necessary to measure the ion energy distribution of the Cylindrical Inertial Electrostatic Confinement Fusion (C-IECF) device in order to confirm this. To do this, we have measured the distribution of the neutral particle beam energy (relative to ion energy distribution). These experimental results demonstrate that a decrease of operation gas pressure (from 1.7 Pa to 0.3 Pa) contributes to the increase in ion energy.