  A compact accelerator design for irradiation purposes is being proposed at
KEK. This design targets an energy of 10 MeV and a current of 50 mA. Current
design includes a 100 kV thermionic DC electron gun with an RF grid, 1-cell
normal-conducting buncher cavity, and Nb$_{3}$Sn superconducting cavities to
accelerate the beam to the final energy of 10 MeV. The goal of the present beam
dynamics study is the beam loss suppression (to the ppm level), since it
results in a thermal load on the cavity. Then the beam performance at the
accelerator exit should be confirmed. The main issue was to transport the beam
without loss, since the initial electron energy (100 keV) is low, and the beam
parameters are intricately correlated. In addition, the space charge effect is
considerable. For this reason, simultaneous optimization of multiple parameters
was necessary. Here we report optimization results and their effect on the
design of the machine.
