SXFEL装置上基于LLRF控制系统的速调管输入输出特性曲线的线性化

发布时间：2018-01-27 15:48

本文关键词： 速调管线性化 SXFEL 查找表　出处：《中国科学院研究生院(上海应用物理研究所)》2017年硕士论文　论文类型：学位论文

【摘要】：大功率放大器的非线性特性给电信系统和高能物理实验带来的不好的影响自上世纪后几十年来一直在被研究。这种非线性特性带来的不好的现象同时也存在于直线加速器中的微波放大器中。直线加速器一般应用于现代粒子物理实验或用户设施中,比如自由电子激光器。上海软X射线自由电子激光(soft X-ray free-electron laser,SXFEL)装置作为国内第一台第四代光源装置,对电子束团的能量稳定性、能散度提出了很高的要求,这就要求高频低电平控制系统对速调管的输出信号进行精确的测量和控制,以保证加速器的稳定运行并且达到其技术指标。然而直线加速器中大功率速调管放大器不理想的非线性放大特性会导致低电平控制系统调节的低效率。本篇论文致力于研究上海软X射线自由电子激光装置中直线加速器的大功率速调管放大器,工作的重点是对其非线性速调管放大特性的研究。我们研究并实现对比了三种基于FPGA的数字预失真速调管线性化算法,所描述的预失真线性化算法模块可以直接放置在低电平模块中,不会影响其他信号。数字预失真方法具有高度的灵活性并可进行精确的线性化,但是需要对速调管的非线性特性进行精确的测量以此来计算出与之特性相反的预失真模块。所以我们首先对速调管的非线性特性进行了实地的测量与分析建模,通过其非线性特性,求出其预失真函数,使用了多项式算法、直接查找表算法以及插值法查找表算法对其预失真函数建模模拟,并在FPGA中将其一一实现并对比分析,最终选取了插值法查找表预失真算法进行线性化设计。本文基于上海软X射线自由电子激光装置,采用基于FPGA的插值法查找表数字预失真方法,在微波低电平控制系统中设计了一套实现高功率速调管放大器线性化的在线系统。经S波段低电平系统和其相应的东芝E3730A速调管及高压调制低电平系统实地测试表明,本文提出的在微波低电平控制系统中建立的在线系统能够有效补偿速调管带来的非线性问题,提高了微波低电平控制系统的精度及准确性,改善了高频低电平系统的性能,满足了上海软X射线自由电子激光试验装置的需求,并且线性化方法具有可移植性。文章还通过对不同高压下的速调管非线性补偿的预失真函数分析,得出推论:在已测得某一高压下的速调管的输入输出特性的情况下,可根据本论文提出的研究方法,对其非线性特性进行线性化处理。在未测得某一高压下的速调管输入输出特性曲线时,可由已知的相邻高压下的预失真函数推断出其预失真函数,从而进行线性化。在相邻高压相差很小的情况下,可认为其中的关系为线性的。
[Abstract]:The negative effects of the nonlinear characteristics of high power amplifiers on telecommunication systems and high energy physics experiments have been studied for decades since 0th century. In microwave amplifiers in line accelerators. Linear accelerators are generally used in modern particle physics experiments or in user facilities. For example, free electron laser. Shanghai soft X-ray free electron laser soft X-ray free-electron laser. As the first 4th generation light source device in China, SXFELL has put forward high requirements for the energy stability and energy divergence of the electron beam cluster. This requires the high-frequency low-level control system to accurately measure and control the output signal of klystron. In order to ensure the stable operation of the accelerator and meet its technical specifications, however, the unsatisfactory nonlinear amplification characteristics of the large power klystron amplifier in the linear accelerator will lead to the low efficiency of the regulation of the low level control system. The high power klystron amplifier of the linear accelerator in Shanghai soft X-ray free electron laser system is studied. The emphasis of the work is the study of the nonlinear klystron amplification characteristics. We have studied and implemented three digital predistortion klystron linearization algorithms based on FPGA. The described predistortion linearization algorithm module can be placed directly in the low level module without affecting other signals. The digital predistortion method has a high degree of flexibility and can be linearized accurately. But it is necessary to measure the nonlinear characteristics of klystron accurately to calculate the predistortion module which is opposite to its characteristics. So we first measure and model the nonlinear characteristics of klystron in the field. According to its nonlinear characteristics, the predistortion function is obtained, and its predistortion function is modeled and simulated by polynomial algorithm, direct lookup table algorithm and interpolation look-up table algorithm. Finally, the interpolation look-up table predistortion algorithm is selected for linearization design. This paper is based on Shanghai soft X-Ray Free Electron Laser device. The interpolation method based on FPGA is used to find the digital predistortion of the table. An on-line system for linearization of high power klystron amplifier is designed in microwave low level control system. The low level system via S band and its corresponding Toshiba E3730A klystron and high voltage modulated low level system are designed. Field tests show that. The on-line system established in the microwave low level control system can effectively compensate the nonlinear problem caused by klystron and improve the accuracy and accuracy of the microwave low level control system. The performance of high frequency low level system is improved and the requirement of Shanghai soft X ray free electron laser testing device is satisfied. And the linearization method is portable. The predistortion function of nonlinear compensation of klystron at different high voltage is also analyzed in this paper. The inferences are drawn that if the input and output characteristics of a klystron have been measured at a certain high voltage, the research method proposed in this paper can be used. When the input and output characteristic curve of klystron is not measured, the predistortion function can be inferred from the known predistortion function of adjacent high voltage. In the case of small difference between adjacent high pressure, the relation between them can be regarded as linear.
【学位授予单位】：中国科学院研究生院(上海应用物理研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN24;TN122

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