A proof of principle experiment has been performed for the in situ measurement of the work function in vacuum conditions (~10−7 torr) relevant to cesium-seeded negative ion sources for fusion applications. The work function is measured using the principle of the photoelectric effect. The performance of the work function measurement setup and temperature-controlled cesium (Cs) oven has been characterized using various diagnostics such as a quartz crystal microbalance, a surface ionization detector and pressure measurements. The background impurities responsible for work function degradation are detected using the residual gas analyzer. The work function (⩽3.06 eV) and Cs flux (~1012 atoms s−1) have been measured directly at the sample surface during controlled Cs evaporation using a novel, inexpensive and portable design of the cathode–anode assembly.
真空条件（10⁻⁶ Torr）下で、核融合用途のセシウムシード負イオン源に関する仕事関数測定実験を実施した。仕事関数は紫外光電子分光法により測定された。本報告では、セシウムシード負イオン源の運転条件下で仕事関数が有意に低下することを実証し、実験結果を示す。さらに、陰極-陽極アセンブリの設計と較正についても詳細に説明する。