  The energy recovery linac test facility (ERL-TF), a compact ERL-FEL (free
electron laser) two-purpose machine, was proposed at the Institute of High
Energy Physics, Beijing. As one important component of the ERL-TF, the
photo-injector started with a photocathode direct-current gun has been
designed. In this paper optimization of the injector beam dynamics in
low-charge operation mode is performed with iterative scans using Impact-T. In
addition, the dependencies between the optimized beam quality and the initial
offset at cathode and element parameters are investigated. The tolerance of
alignment and rotation errors is also analyzed.
