Development of 1.6-cell RF gun for generation of high efficiency and extremely short FEL pulse

A 1.6-cell photocathode RF gun was developed for generation of high efficiency and extremely short FEL pulse in Kyoto University FEL. The requirements of the RF gun are to suppress discharge in long macro-pulse electron beam, which is required FEL oscillator, and to apply dynamic cavity desynchronization (DCD) to achieve high efficiency of FEL. In order to achieve the requirements, electromagnetic field analysis and beam tracking simulation were carried out. In the beam tracking simulation for the DCD operation, 1.4-cell shape and 1.6-cell shape, which were satisfied the requirement to suppress the discharge, were used to investigate the relation between the acceleration phase and the arrival time at the RF gun exit. The simulation results show that the 1.6-cell shape is applicable to the DCD operation. Based on the simulation results, the 1.6-cell photocathode RF gun was designed. After the fabrication of the 1.6-cell RF gun, the resonant frequency and the longitudinal electric field distribution were measured, and the measured results well agreed with the design performance. (author)