Recent advancements in electron beam compression methods have enabled the production of ultrashort electron beams at the sub-femtosecond scale, significantly expanding their applications. However, the temporal resolution of these beams is primarily limited by the flight time jitter, especially during their generation in photocathode RF electron guns. In this paper, to mitigate the impact of microwave phase jitter on the flight time jitter inside the electron gun, we designed a 2.3-cell X-band electron gun, which enables the electron beams to acquire maximum output energy and minimum in-gun flight time at the same injection phase. Moreover, the tolerance of the cavity's machining errors is assessed and the RF input coupler of this cavity has been designed. Our simulation results indicate that this design provides a solid foundation for further improving the temporal resolution of the electron beam.

Hefei Advanced Light Facility (HALF) injector comprises 40 S-band 3-meter traveling wave accelerating structures, capable of delivering electrons of full energy 2.2 GeV into the storage ring. To mitigate the emission degradation caused by dipole and quadrupole fields in the coupler cavity, the coupler design incorporates a racetrack and a short-circuit waveguide to eliminate this impact. This article presents an introduction to design of the traveling wave structure and the results of cold and high-power testing. We performed tuning and preliminary measurements on accelerating structure, resulting in meeting the single-cell phase deviation and accumulated phase deviation requirements of the project objectives while maintaining good measurement consistency.

Recent advancements in electron beam compression methods have enabled the production of ultrashort electron beams at the sub-femtosecond scale, significantly expanding their applications. However, the temporal resolution of these beams is primarily limited by the flight time jitter, especially during their generation in photocathode RF electron guns. In this paper, to mitigate the impact of microwave phase jitter on the flight time jitter inside the electron gun, we designed a 2.3-cell X-band electron gun, which enables the electron beams to acquire maximum output energy and minimum in-gun flight time at the same injection phase. Moreover, the tolerance of the cavity's machining errors is assessed and the RF input coupler of this cavity has been designed. Our simulation results indicate that this design provides a solid foundation for further improving the temporal resolution of the electron beam.

Hefei Infrared Free-Electron Laser device (IR-FEL) is a user experimental device dedicated to energy chemistry research that can generate high brightness mid/far infrared lasers. It is driven by an S-band linear accelerator with a maximum electron energy of 60 MeV. The stability of the final output laser is determined by the energy stability and spread of the electron beam, and the Low-Level RF control system (LLRF) is opitimized to improve the energy stability of the electron beam. There are two klystrons in the linear accelerator of IR-FEL, and the periodic oscillation of out power output of the klytrons is existed (approximately ± 0.2%~2% for amplitude). The oscillation period of two klystrons are exchanged in the case of exchanging the filament power supplies of two klystrons. The pulse-to-pulse feedforward and in-pulse feedback algorithm are developed to compensate the periodic fluctuations of the output power of the klystrons, and the IQ demodulation is changed to the Non-IQ demodulation (13/3) to separate and suppress the odd harmonic. After the optimization, the stability of klystron output signal has been improved from 0.12%/0.07° (rms) to 0.04%/0.09° (rms).

The Hefei Advanced Light Facility (HALF) is a diffraction-limited storage ring-based light source consists of a 180 m linear accelerator and a 480 m storage ring. The RF reference signal included 499.8 MHz and 2856 MHz are generated from two phase-locked master oscillators and transmitted to the RF system, beam position monitor system, timing system and beamline station by the phase stabled coaxial cables which are installed in the ±0.1℃ thermostatic bath. The RF Reference Distribution System (RF-RDS) are developed to realize the phase synchronization and transmission with low phase noise for long distance. The continues wave amplifier is manufactured to generate RF power of 10 W, with the added phase noise being less than 1 fs (10 Hz~10 MHz). The phase noise of each receiving terminal is estimated to be less than 30 fs (10 Hz~10 MHz). The design of RF-RDS and experimental result are discussed in this paper.