Performance of an Indium-sealed S-band RF Photoelectron Gun for Time-resolved Electron Diffraction Experiments

• Published in: Journal of the Korean Physical Society Vol. 74; no. 1; pp. 24 - 29
• Main Authors: Kim, Hyun Woo, Jang, Kyu-Ha, Baek, In Hyung, Lee, Kitae, Jeong, Young Uk, Nam, Jinhee, Chae, Moonsik, Kim, Mi Hye, Kim, Young Chan, Oang, Key Young, Park, Sunjeong, Han, Jang-Hui, Vinokurov, Nikolay A.
• Format: Journal Article
• Language: English
• Published: Seoul The Korean Physical Society 01.01.2019; Springer Nature B.V; 한국물리학회
• Subjects: Accelerators; Brazing; Electron beams; Electron diffraction; Electrons; Emittance; Energy measurement; Experiments; Free electron lasers; Holes; Indium; Mathematical and Computational Physics; Particle and Nuclear Physics; Photocathodes; Photoelectrons; Physics; Physics and Astronomy; Quantum efficiency; Radio frequency; Superhigh frequencies; Theoretical; 물리학; Ultrafast science; Radio-frequency gun; Time-resolved electron diffraction; Photoelectron gun; Ultrafast electron diffraction
• ISSN: 0374-4884; 1976-8524
• DOI: 10.3938/jkps.74.24

We have developed a one-and-half -cell S-band radio-frequency (RF) photoelectron gun (photogun) fed by a coaxial coupler. The RF photogun is dedicated to ultrafast-electron-diffraction experiments by generating electron bunches of 3-MeV energy and a-few-pC charge, which is not strict condition compared to those for X-ray free-electron lasers. Brazing of RF cavities is welldeveloped process for making RF guns or RF accelerators. Sometimes, however, a failure occurs in the brazing process, causing the entire electron gun or accelerating cavity to spoil. Axial-symmetric design of the RF photogun permits indium sealing for cavity cells, a photocathode plate, and a coupling RF part. We firstly report that the indium-sealed RF photogun successfully meets the required performance and long-term stability for ultrafast electron diffraction experiments. We have stably operated the RF photogun for more than three years with the electron beam conditions of ~ 3-MeV energy, up-to-10-pC charge, and a repetition rate of 50 Hz. The quantum efficiency of the copper photocathode had improved from 10 −6 to 10 −5 depending on vacuum condition from 10 −8 to 5 × 10 −10 Torr, respectively. Measured emittance and energy spread of the generated electron beam showed 0.3 mm-mrad and less than 0.25%, respectively, for a bunch charge of ~ 2 pC, which agree well with those obtained by ASTRA simulation.