Parameters stability of S-Band RF gun cavity due to effects of pulsed RF heating

Requirements to high performances of modern Free Electron Lasers (FEL) facilities transform to requirements of high stability of their electron injectors, which are typically based on photocathode RF guns. To provide high brightness bunches, gun cavities operate in the injector with high pulsed electric, hence, magnetic fields. The effects, related to a pulsed RF heating, result in the change of resonance frequency and quality factor of the cavity even during few mu s RF pulse that, in turn leads to the amplitude and the phase change of RF oscillations in the gun cavity. Cavity deformations due to pulsed heating are considered and corresponding deviations in the cavity resonance frequency are evaluated. Resulting deviations in the phase and the amplitude of the RF field in the cavity are estimated in dependence on the RF pulse duration.