在“神龙二号”直线感应加速器的调试中,虽然电容探头和电阻分压器测到的空载加速腔电压波形基本一致,但是带束流负载时两者的波形有明显差异,针对此实验现象开展了研究。仔细模拟了束流波形和电压波形相对时间差异引起的波形差异,得到束流提前、同步和滞后条件下的腔压波形,确认相对时间差是导致波形差异的一个重要原因。建立了加速腔的分布参数电路模型,模拟结果表明束流负载效应到达两种探头的时间不同,这会导致腔压波形的不同; 由于电容探头距离加速间隙更近,所以电容探头测到的波形更接近束流实际得到的加速波形。后续的调试实验获得了没有加速电压时束流产生的负载效应波形,证明束流负载到达两个探头的时刻确实不同,对加速器出口束流能谱的测量结果也表明束流的能谱分布和电容探头波形的叠加结果基本符合,上述结果表明该研究所用的模拟和分析方法是有效的,可以用于加速器的调试和性能优化。

In the commissioning of a linear induction accelerator, cavity voltage waveforms measured by capacitor voltage probe (CVP) and resistor divider were almost the same when there was no beam load. The waveforms were different when there was a beam load. This phenomenon was then researched. Cavity voltage waveforms were simulated when the beam was advanced, synchronized and delayed. Simulation results showed that time difference caused by cavity structure was the main reason for the waveform differences. The distribution parameter circuit model of the accelerating cavity was created. It was shown that the beam load arrived at the two probes by different moments, which would lead to the difference of the cavity waveforms. The waveform measured by CVP was closer to the real accelerating waveform because that the CVP was nearer to the accelerating gap. The measured beam load waveforms verified that the beam load arriving times of two probes were different. The measured energy spectrum of accelerated beam was also consistent with the addition of CVP waveforms. As a result, the simulation and analysis methods in this research were effective. They would be used in commissioning and performance optimization of the accelerator.