We developed an electron gun system capable of delivering high brightness beams to drive soft x-ray free-electron lasers (SXFEL). We modified the conventional radio-frequency (rf) gun concept by using a 50-kV gun with a gridded thermionic cathode connected with a 238-MHz acceleration cavity. We achieved a low target emittance by applying the following two methods: (1) to obtain a parallel beam after the control grid, we optimized the grid voltage to compensate for the electric potential distortion near the grid (i.e., the lens effect); and (2) to avoid emittance growth due to the space charge effect at low energy regions, the 50-kV gun was connected to a 238-MHz rf cavity with a minimum distance, which immediately accelerated the beam energy to 500 keV. We built a gun test stand to verify the high beam performance, i.e., a normalized emittance of less than 4 mm mrad with a bunch charge of 1 nC and a pulse length shorter than 0.7 ns, as predicted by cst and parmela codes. Our proof-of-performance experiments demonstrated that a projection emittance of 1.7 mm mrad was obtained as a core part, representing 60% of all extracted electrons and the measured emittance agreed well with the simulation value of 2.0 mm mrad. This paper presents an overview of the electron gun system and our proof-of-performance experimental results.

中文翻译：

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使用栅状热电子阴极的低辐射射频电子枪

我们开发了一种电子枪系统，该系统能够发出高亮度光束，以驱动软X射线自由电子激光器（SXFEL）。我们通过使用50 kV枪和带有238 MHz加速腔的网格状热电子阴极，对传统的射频（rf）枪概念进行了修改。我们通过以下两种方法实现了较低的目标发射率：（1）在控制栅极之后获得平行光束，我们优化了栅极电压以补偿栅极附近的电势失真（即透镜效应）；（2）为避免由于低能量区域的空间电荷效应而导致发射率增长，将50 kV喷枪连接到最小距离的238 MHz rf腔，该腔立即将束能量加速至500 keV。我们建造了一个枪支测试台以验证远光灯性能，即cst和parmela代码。我们的性能证明实验表明，获得了1.7 mm mrad的投影发射率作为核心部分，占所有提取电子的60％，并且测得的发射率与2.0 mm mrad的模拟值非常吻合。本文概述了电子枪系统以及我们的性能证明实验结果。