The proposed TRIUMF ARIEL project plans to build a 50 MeV electron linac at 10 mA to produce radioactive ion beams through photo-fission. The electron linac includes two major parts: injector section and driver linac. The injector section is required to accelerate electron beams from 100 keV to 10 MeV, and the following driver linac boosts the energy from 10 MeV to 50 MeV. The electron initial energy from the thermionic gun is 100 keV and 171 ps bunch length with a repetition rate of 650 MHz. Several variants of configurations have been proposed and studied to get an optimized solution. Simulations show that with careful design and specific input parameters after the gun, the beam at 50 MeV can be bunched into 11.75 ps (5.5° at 1.3 GHz) with the maximum beam size inside the superconducti