Abstract
A conventional free electron laser (FEL) is bulky and expensive. In order to quickly build up the FEL power in a short undulator, a laser technology has been proposed to generate a pre-bunched electron pulse-train with a THz bunching frequency from a photoinjector*. The bunching factor** of an accelerated pulse-train beam is influenced by the beam radius, initial bunching frequency, space charge force, acceleration gradient, and acceleration phase in an accelerator. For a given RF accelerator and initial beam parameters, there is a limitation on the maximally attainable bunching factor and bunching frequency for the accelerated pulse-train beam. This paper presents a theoretical analysis for the bunching factor and bunching frequency of an accelerated pulse-train beam subject to nominal initial beam conditions in a photoinjector. The theoretical analysis is compared with the simulation results from the simulation code, PARMELA. To obtain an output bunching factor larger than 0.5%, our simulation study indicates that the maximum bunching frequency at the cathode is 25 THz for a 150 A beam current under a peak acceleration field of 80 MV/m