A neutron source with a flux of 0.1 MW/m2 has been considered as the preliminary-stage irradiation test facility for the development of fusion reactor materials by use of plasma-based neutron sources. From the results of Fokker-Planck simulations using realistic parameters, it was found that the homogeneous 14-MeV neutron flux over 0.1 MW/m2 is obtained for the area of ∼3 m2, even if Te = 0.2 keV. This means that a mirror-based neutron source for the preliminary testing can be designed and constructed with the current database.