On a possibility to suppress microwave instability in storage rings using strong longitudinal focusing

Abstract

Microwave instability has been observed in almost all operational storage rings. It causes anomalous bunch lengthening and energy spread growth. Microwave instability appears to be the main limiting factor in both longitudinal brightness of the electron beam and the achievement of very short bunches [1,2]. The 6D brightness of an electron beam is the main figure of merit for applications in the generation of bright and coherent short wavelength light. Storage rings can to provide beams with extremely high transverse brightness [3] sufficient for X-ray FELs. The main limiting quality factor for electron beams in storage rings is longitudinal brightness. In this paper a possibility for suppressing or eliminating microwave instability using an advanced RF system and strong focusing in the longitudinal direction is discussed. Some examples of strong longitudinal focusing based on inverse mm-FEL are presented.