Evolution of a storage ring free electron laser micropulse in a macropulse zone

We observed the evolution of micropulses of the storage ring free electron laser (SRFEL) in a macropulse zone with the compact storage ring NIJI-IV, and we showed that a simple simulation based on one-dimensional finite difference equations could express the characteristics of the micropulse. The calculated width of the micropulse was roughly in accord with the observed pulse width. Moreover, we showed that the macropulse intensity and the energy spread were approximately expressed by simple functions when there was only longitudinal detuning. Using these expressions for the macropulse intensity and the energy spread, we clarified that the pulse height of the intensity was greater than twice the difference between the average intensity and the minimum intensity to maintain the macropulse zone. It was also observed that the period of the increase of the energy spread in a macropulse depends negligibly on the detuning length, and this rule for the macropulse was approximately explained using simple expressions. We will be able to apply the simple simulation to investigate the peak power in a Q-switch operation.