멀티포트 전자총 내부에 생성되는 가속전장의 대칭성 연구

Abstract

This thesis describes an analysis, design and low-power test of an S-band photocathode rf gun for the X-ray free electron laser (XFEL) at the Pohang Accelerator Laboratory (PAL). We have analyzed the emittance growths due to the high-order fields. In this analysis, the monopole, dipole, quadrupole, sextupole, and octupole fields have been considered. To reduce the rf emittance growths induced byhigh-order fields in the rf gun, we have also analyzed how to eliminate the high-order fields in the rf gun by applying the principle of superposition. Two model cavities with tunable ports have been fabricated and tested with the low power at the PAL. These are the single-feed rf gun with three pumping ports and the dual-feed rf gun with two pumping ports. Finally, we have selected the dual-feed rfgun with two pumping ports for PAL-XFEL. In this rf gun, the coupling scheme, dimensions of cell-to-cell iris, and the radius of coupling hole have been changed to improve the performance of the rf gun. As of June 15, 2011, the rf gun is in the commissioning at the gun test facility at the PAL.