Simulation for spectral evolution of a storage ring free electron laser in a macropulse zone

A computer simulation for evolution of a storage ring free electron laser (SRFEL) micropulse in a macropulse zone has been performed. The one-dimension simulation based on the bunch heating theory could describe dependence of the macropulse period on the longitudinal detuning length and evolution of the pulse width. We modified the simulation code so as to describe the evolution of the SRFEL spectrum. It can explain the characteristics of the NIJI-IV SRFEL spectrum in the macropulse zone. The evolution of the spectral width and wavelength in the macropulse zone is discussed.