We have been developing a 1-D PIC simulation code for the spherical IECF, which includes atomic processes between energetic particles and background gases. In this paper, the electrode spacing effects on the neutron production rate (NPR) are investigated using this code by changing the cathode radius while keeping anode radius constant (17cm). Applied voltage (-90 kV) and ion injection current (50mA) are fixed with a deuterium pressure of 0.13 Pa, where the IECF discharge is not self-sustaining discharge and is in the ion injection mode.

It is found that (1) the discharge voltage is not affected by the electrode spacing, (2) the neutron production rate increases with the increase of the cathode radius, and (3) the maximum obtained NPR with cathode radius of 10cm is about twice of that with the 3cm cathode.