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김현우,장규하,백인형,이기태,정영욱,남진희,채문식,김미혜,김영찬,왕기영,박선정,한장희,Nikolay A. Vinokurov 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.1
We have developed a one-and-half -cell S-band radio-frequency (RF) photoelectron gun (pho- togun) fed by a coaxial coupler. The RF photogun is dedicated to ultrafast-electron-diraction 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 well- developed 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 rstly report that the indium-sealed RF photogun successfully meets the required performance and long-term stability for ultrafast electron diraction 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 eciency of the copper photocathode had improved from 106 to 105 depending on vacuum condition from 108 to 5 1010 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.