绝缘问题是高电压、高场强器件和设备中不可回避的问题，是决定器件、设备运行参数和稳定性的重要因素。针对一台直线感应加速器调试中出现的加速腔绝缘环在带束负载情况下的真空沿面闪络现象，进行了分析和研究。分析表明，在排除设计、材料、加工、洁净和真空度等常规异常因素后，导致绝缘环真空沿面闪络的可能因素是电子在绝缘环表面的吸附和累积，绝缘环上累积的电子来源和加速器中加速、传输的电子束的丢失有关。从加速腔工作状态出发，分析绝缘环表面积累电荷和丢失电子束的相关途径，进而提出相应的技术措施，以提高加速腔运行稳定性。

Flashover across the insulator in induction cavity with electron beam load once occurred frequently, which affected the performance parameters and stability of the high voltage high current devices and equipment. This paper studies the vacuum surface flashover across the insulator in the induction cavity of a linear induction accelerator under debugging. After excluding design and fabrication of the insulator as well as cleanness and vacuum degrees, it is found that the electrons from the plasma induced by high energy electrons interacting with the gas adsorbed on the inner cavity wall might play the key role of flashover. These thermal electrons move randomly and some of them will reach and stay on the insulator surface for some time, and flashover happens when high electric field is applied across the insulator with accumulated electrons.