Beam-based measurement of LCLS-II injector solenoid misalignments

Solenoid focusing is commonly used in accelerators for electron-beam containment and to compensate for space-charge induced emittance growth at low beam energies. However, misalignment between the solenoid field and the beam trajectory can result in degraded emittance compensation due to orbit kicks, dispersive effects, and non-linearities in the magnetic field profile. This paper presents a technique for beam-based measurement of solenoid misalignments, using expressions derived from a hard-edged solenoid linear transfer matrix with known beam parameters. The results of measurements conducted at the LCLS-II injector are presented as a validation of this method, along with simulation studies that estimate the impact of solenoid misalignments on emittance growth.