  Coupler RF kick due to the asymmetric structure caused by the coupler, is
more likely to lead to emittance growth in the SHINE injector with low beam
energy. The calculation of coupler RF kick and resulting emittance dilution has
been studied in detail in the literature. In this paper, a novel approach is
provided that a lossy material is placed on the surface of the superconducting
cavity to approximate the Q0 of the TESLA cavity, and a frequency solver of CST
is used to simulate the electromagnetic field distribution, which is used to
calculate coupler RF kick, and calibrated against the results of CST Particle
Tracking Studio with a good agreement. In order to minimize the emittance
growth of SHINE injector, a 1.3 GHz symmetric twin-coupler cavity is adoped in
the single-cavity cryomodule, and the rotational angle and permutation of the 8
cavities in the 8-cavities cryomodule is optimized. Ultimately, the optimized
emittance is lower than the design parameter.
