超快高频谐波斩波器的研究

Chopping systems with fast rise-and-fall time, high repetition rate，high deflection voltage and variable pulse length were required in many accelerators to divert the unwanted bunches to the absorber， and provide the required bunch patterns for special physics experiments. These specifications combined together, are well beyond the state-of-art of traditional pulsed power supplies. An alternative method, investigated here, is to synthesize a continuous train of such short or long pulses by summing a sufficient number of cosine waves at harmonic frequencies of the kicking repetition frequency. With this method，the technology challenges for providing the required pulses with sigle pulsed power supplies are avoided . The optimization of the kicking waveform, the electronic device to get the harmonic waves, the design and optimization of the main deflection structure and the bench measurements of the kicking waveform on the existing slow-wave structure will be studied here. And finally，we will give a technical design report for a fast chopper system which could divert as much as 99% of the 162.5 MHz，2.1 MeV proton bunches to the absorber，but only leaves 1% to bombard the target，which could be used to measure the neutron energy spectra with standard pulsed-beam time-of-flight methods.

许多加速器设备里都会用到快升降、高冲频、高偏压且可灵活调整脉冲长度的束团斩波器来踢除不需要的束团，以满足特定物理实验的需求。其技术需求已经远远高出了当前脉冲功率源所能达到的水平。一个很好的替代解决办法是通过一系列工作在冲击频率整数倍频上的谐波叠加来近似得到所需要的周期性连续长/短脉冲，从而避免了从单一功率源获得所需脉冲信号的各种技术挑战。本研究从谐波叠加方案的优化，产生谐波的硬件电路板的研制，斩波器的主偏转硬件的优化和设计，及叠加谐波在现有慢波设备上的测试等方面展开。最后，我们会结合国内现有的强流质子加速器，给出一个超快高频谐波斩波器的设计报告，通过该斩波器，可最高实现162.5 MHz，2.1 MeV的连续质子束团中，99%的束团被踢出，只留下1%的束团打靶，以满足利用飞行时间法测中子能谱所需要的束团间隔。

随着现代高功率强流连续波直线超导加速器的发展，其可以提供的连续波束流流强远高于单个终端的需求，其能量连续可调且可在不同能量上灵活引出，从而可以覆盖多种工业和实验需求，且其连续波流强已经远远高于单个实验终端的需求。通过多个倍频谐波叠加可以得到快升降、高冲频、高偏压的斩波脉冲，从而对时间间隔在ns量级的连续波束团实现单束团的筛选，以满足特定物理实验的需求。通过调节单频射频谐振腔的频率以及束团相对于腔体的同步相位，使得处于不同相位上的束团获得不同的偏转效果，从而将初始束团均匀或非均匀地分成两到三束。结合基于多个倍频谐波叠加的单束团筛选分束装置和基于单频射频谐振偏转腔的均匀或非均匀分束装置，在不同能量上将束流根据终端需求通过初级分束装置引出一部分，并进一步通过次级分束装置分配到多个终端，将极大提高强流束的利用效率。本项研究主要包括基于多个倍频谐波叠加偏转腔和单频偏转腔的射频分束方案设计，不同能量质子束对应特定偏转角所需要的偏转电压推导，方案中所需要用到的射频偏转硬件，及单频的或混频的，常温的或超导的射频偏转腔的设计；用于混频谐波腔功率馈入系统的一个三频信号源的研制及测试等等。