Quasi-Isochronous Optics for Sub-Picosecond Bunch Length at Pohang Light Source

Abstract

A lattice design was developed for a quasi-isochronous storage ring, which may produce a sub-picosecond bunch length at the 2.5 GeV Pohang Light Source (PLS) and the analysis of transverse and longitudinal particle dynamics in the designed ring was performed. Small momentum compaction factors in the PLS storage ring were obtained by varying the dispersion function to be negative in bending magnets. The shortest bunch length in the designed ring was estimated to be less than 1 ps, which is three-tenths that of a normal operation. The effects of the second-order momentum compaction factor on the transverse and longitudinal particle dynamics in the quasi-isochronous ring were investigated. The relationship between the momentum compaction factor and the bunch length, which can be obtained in the quasi-isochronous PLS storage ring was also investigated. Multiparticle tracking simulations were performed to investigate the longitudinal beam instability in the quasi-isochronous ring using a broadband impedance model.