采用光学诊断和电磁测量相结合的方法对“强光一号”不同结构的水开关的放电特性进行研究,其中包括环-板结构、球-板结构及局部场增强球-板结构。通过理论模拟开关电场分布及“强光一号”加速器水开关击穿电压的实际测量可以分析不同结构的开关工作稳定性,结果表明:环-板结构的水开关具有最稳定的击穿特性,15发放电的时间抖动只有30 ns;局部场增强球-板结构水开关抖动60 ns;球-板结构水开关稳定性最差,抖动达到140 ns。利用纳秒时间分辨可见光分幅相机和光纤传感器对环-板型及局部场增强球-板结构水介质开关进行光学测量,得到了电流通道发展图像以及整个放电过程的光强变化信号。实验结果表明:环-板型水介质开关开始击穿时的平均场强约为190 kV/cm,同时存在多个放电通道,流注呈树枝状分布,其发展速度为几十cm/s。

The behaviors of three kinds of self-breakdown water switches for Qiangguang-Iaccelerator were studied. They have different configurations including sphere-plane structure,local field-enhanced sphere-plane structure and annulus-plane structure. By computer simulation,the electric field parameters were determined. The breakdown characteristics of the switches were tested in Qiangguang-Ifacility. Experimental results of three different kinds of switches show that the annulus-plane structured has the switch stablest breakdown performance. The time jitter of the annulus-plane switch for 15 shots is only 30 ns,comparing the 60 ns and 140 ns of the local field-enhanced sphere-plane structure and the sphere-plane structure respectively.In addition to the standard electrical diagnostics,optical diagnostics of the breakdown phase were studied with a fast framing camera. The experiment results show that the average breakdown electric field of annulus-flat water switch is about 190 kV/cm,several discharging channels are observed at the same time,the streamers appear like bush and their velocity is about tens of centimeters per second.