Compensation of emittance and bunch length variations induced by insertion devices with damping wigglers in fourth-generation light sources

Recent investigations suggest that in a fourth-generation light source, where both fundamental-frequency and harmonic RF cavities are commonly used for bunch lengthening, variations in radiation energy loss per turn (U0) could cause a significant variation in bunch length.  It is therefore necessary to compensate for the U0 variations caused by changes in the gaps of the insertion devices (IDs). In this paper, we investigate a scheme based on two horizontal or two vertical damping wigglers to simultaneously compensate for horizontal emittance and U0 variations induced by IDs.

A theoretical analysis and an application example are presented.