THPI037  粒子源  8月1日 国際科学イノベーション棟5階 ホワイエ 13:30-15:30
Improvement of the in-site work function measurement system for CeB6 cathodes used in the electron gun of SACLA by impedance matching of the signal line
○馬込 保(高輝度光科学研究センター・理研放射光科学研究センター),渡川 和晃,稲垣 隆宏,原 徹,田中 均(理研放射光科学研究センター)
○Tamotsu Magome (JASRI / RIKEN SPring-8 Center), Kazuaki Togawa, Takahiro Inagaki, Toru Hara, Hitoshi Tanaka (RIKEN SPring-8 Center)
A CeB6 thermionic cathode is used for the electron gun of the X-ray free-electron laser, SACLA. An operation time of a CeB6 thermionic cathode is typically limited to only one year or so due to decrease in emission currents. Since a work function is the most dominant factor in emission current, we have been developing an in-situ measurement system for the work function of the CeB6 thermionic cathode under simulative conditions of the real electron gun to investigate mechanism of this cathode degradation. The developed system adopts the photoelectron yield spectroscopy using excitation lights from a nanosecond tunable Nd:YAG laser system. In the measurement system, the photoelectron pulse signal was distorted in profile because of reflections of the photoelectron pulse signal in the simulative anode plate ( 12 cm in diameter and 2 mm in thickness ) of the real electron gun and in the signal line in vacuum. A coaxial cable of 50 ohms in impedance in vacuum and an anode cylinder ( 5 mm in diameter and 9 mm in length ) enabled the photoelectron pulse signal to be a single nanosecond pulse with a long tail. In this paper, we report the detail of the impedance matching.