Beam dynamics simulation of the solenoid sextupole error in the lcls-ii injector ∗

The LCLS-II injector is a high brightness, high-repetition rate RF injector that consists of a 186 MHz VHF photoelectron gun, a focusing solenoid, a buncher cavity, another focusing solenoid, and a superconducting accelerating cryomodule to boost the electron beam energy to final 100 MeV. The solenoids provide transverse focusing and emittance compensation for the electron beam. However, in reality, the solenoid is not perfect due to manufacturing errors. Especially, the sextupole error in the solenoid field, which can cause significant beam emittance growth. In this paper, we report on the beam dynamics study of the effects of sextupole errors in the current LCLS-II injector.