Superconducting solenoid optimization and field measurements

Abstract A solenoid is typically used in normally conducting and superconducting radio frequency (SRF) photoinjectors to compensate for the projected transverse beam emittance. In the ELBE SRF Gun-II, a superconducting solenoid is positioned inside the gun cryomodule approximately 0.7 m from the end of the gun cavity. The spherical aberration and multipole field effects caused by offset and tilt limit the reduction in beam emittance for high bunch charges. We designed a novel superconducting (SC) solenoid with a lower spherical aberration coefficient. In the simulation, the beam emittance from the spherical aberration decreased by 47%. Both the longitudinal and transverse fields were measured and analyzed using the formalism fitting method to assess the performance of the SC solenoid within the cryomodule and its influence on the beam transverse emittance.