基于谐振腔的直线加速器束流多参数诊断技术研究

Linac-based X-Ray free electron laser has been the frontier in the research of the fourth generation light source. In order to measure the linac beam emittance, bunch length and other parameters on line, technologies of multi-parameter beam diagnostics based on resonant cavities are proposed and applied at Hefei Light Source high brightness injector. As pick-up stations for beam diagnostics, resonant cavities can provide signal with large amplitude and high SNR and help to achieve high precision. In this project, method of measuring beam intensity and bunch length simultaneously by a same cavity is first put forward for low repetition and short bunch situation, while a new approach to measure peak current of photocathode RF gun is showed. The TM0n0 eigenmodes of cavities are used in combined measurement of bunch length, beam intensity, position and quadrupole moment so that the whole diagnostic system is simplified and compact. More than one eigenmodes of resonant cavities are used in beam intensity measurement in order to get higher precision. High speed data acquisition system consists of high speed ADC, high density FPGA and high performance DSP chips is used as signal processing system and the sampling rate can be 1Gsps. All these technologies are available for other linacs at home and abroad.

基于直线加速器的X射线自由电子激光是第四代光源研究的前沿热点。为了解决长期以来在直线加速器中难以实时在线精确测量束流发射度、长度等参数的问题，提出了基于谐振腔的束流多参数诊断技术，并应用于合肥光源高亮度注入器。谐振腔作为束流诊断的拾取装置，可以提供大幅度和高信噪比的束流信号，使测量达到很高的精度。本项目首次提出了利用同一谐振腔同时测量低重复频率短束团情况下的束团长度与束流流强的方法，并给出了一种测量光阴极微波电子枪束流峰值流强的新手段。利用谐振腔的TM0n0模式实现束团长度与束流的流强、位置及四极分量的联合诊断，使整个诊断系统大为紧凑。使用谐振腔的多个特征模式进行束流流强诊断，提高了测量精度。为了处理束流信号，使用高速ADC、高密度FPGA和高性能DSP搭建高速数据采集系统，采样率最高可达1Gsps。这些研究成果可广泛应用于国内外其它直线加速器。

基于直线加速器的X射线自由电子激光是第四代光源研究的前沿热点。为了解决长期以来在直线加速器中难以实时在线精确测量束流发射度、长度等参数的问题，本项目提出了基于谐振腔的束流多参数诊断技术，重点围绕束团长度测量进行研究。谐振腔作为束流诊断的拾取装置，可以提供大幅度和高信噪比的束流信号，使测量达到很高的精度，但是，传统的谐振腔束团长度监测器使用基模TM010模式提取束流信号，由于谐振腔的尺寸不能小于束流管道，基模的能达到的频率上限受到限制，无法测量较短的束团。本项目利用谐振腔的 高次模TM0n0 作为测量模式，使得测量模式的频率上限不再被限制，因此可以测量较短的束团，对未来先进的硬X射线光源的束流诊断有突出的作用。同时，可以实现束团长度与束流的流强、位置及四极分量的联合诊断，可以使整个诊断系统大为紧凑。这些研究成果可广泛应用于国内外直线加速器设施。