Design improvements of electron gun for PAL klystron

IF 0.9 4区 物理与天体物理 Q3 PHYSICS, MULTIDISCIPLINARY
S. J. Park, C. K. Min, Y. G. Park, S. D. Jang, G. Y. Jang, H. S. Shin
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引用次数: 0

Abstract

Several prototype S-band pulsed klystrons for use at the Pohang Accelerator Laboratory (PAL) have been developed by a domestic company in collaboration with PAL. These klystrons successfully achieved the required RF output power at a low repetition rate (< 30 Hz) but suffered from gun arcing when operated at 60 Hz, which is the repetition rate required for the PAL-XFEL. Post-mortem inspection revealed that the arcing spots on the focusing electrode (Wehnelt) were not located at the regions of maximum electric field. Particle trajectory simulations in the electron gun region suggest that the initial arcing is triggered by electron emission and followed by clump-induced breakdown processes. In addition, vacuum breakdown can be initiated from the so-called triple point (TP) at the lower end of the ceramic insulator, where a negative potential is applied during high-voltage (HV) operation. Further numerical simulations confirmed that electrons emitted from this TP can travel along the ceramic surface, undergo multiplication, and eventually cause breakdown near the anode housing. Based on these findings, we propose design improvements—most notably enhanced cleaning and polishing procedures as well as an added electric field shield near the TP—to suppress vacuum breakdown at higher repetition rates (e.g., 60 Hz). Initial high-voltage (HV) processing data show that the improved gun design significantly reduces arcing events, enabling stable klystron operation.

PAL速调管电子枪的设计改进
国内一家公司与浦项加速器实验室(PAL)合作开发了用于浦项加速器实验室(PAL)的几种s波段脉冲速调管原型。这些速调管在低重复频率(< 30hz)下成功地实现了所需的RF输出功率,但在60hz (PAL - xfel所需的重复频率)下工作时,会产生电弧。解剖检查发现聚焦电极(Wehnelt)上的圆弧点并不位于最大电场区域。电子枪区域的粒子轨迹模拟表明,初始电弧是由电子发射触发的,随后是团块诱导击穿过程。此外,真空击穿可以从陶瓷绝缘体下端的所谓三相点(TP)开始,在高压(HV)运行期间,在那里施加负电位。进一步的数值模拟证实,从该TP发射的电子可以沿着陶瓷表面传播,进行倍增,并最终在阳极外壳附近引起击穿。基于这些发现,我们提出了设计改进——最显著的是加强清洁和抛光程序,以及在tp附近增加电场屏蔽——以抑制更高重复率(例如60 Hz)的真空击穿。初始高压(HV)处理数据表明,改进后的枪设计显著减少了电弧事件,使速调管工作稳定。
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来源期刊
Journal of the Korean Physical Society
Journal of the Korean Physical Society PHYSICS, MULTIDISCIPLINARY-
CiteScore
1.20
自引率
16.70%
发文量
276
审稿时长
5.5 months
期刊介绍: The Journal of the Korean Physical Society (JKPS) covers all fields of physics spanning from statistical physics and condensed matter physics to particle physics. The manuscript to be published in JKPS is required to hold the originality, significance, and recent completeness. The journal is composed of Full paper, Letters, and Brief sections. In addition, featured articles with outstanding results are selected by the Editorial board and introduced in the online version. For emphasis on aspect of international journal, several world-distinguished researchers join the Editorial board. High quality of papers may be express-published when it is recommended or requested.
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