RF measurement and high-power test of a 1.6-cell photocathode RF gun at Pohang Accelerator Laboratory

Abstract

A Brookhaven National Laboratory (BNL) GUN-IV type photocathode rf gun has been fabricated to use in femto-second electron diffraction (FED), the femto-second far infra-red radiation (fs-FIR) facility, and the X-ray free electron laser (X-FEL) at the Pohang Accelerator Laboratory (PAL). The gun consists of a 1.6-cell cavity with a copper cathode, a solenoid magnet, beam diagnostic component and auxiliary systems. The dimensions of the cavity that provided the desired resonant frequency were determined by using the SUPERFISH code. The change in the resonant frequency due to the laser port and the wave-guide port on the cavity wall was estimated with Slater's perturbation theorem. The size of the ports was finalized by using a series of cutting and measuring processes. A method to measure the resonant frequency of the cavity during the operation was developed. Finally, the microwave and the basic beam parameters were measured carefully to confirm the successful fabrication of the photocathode RF gun system.