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在上海软X射线自由电子激光(Soft X-ray Free-electron Laser,SXFEL)中的微波低电平控制系统中,通过对各速调管的输出信号进行测量和控制,保证加速器的稳定运行并且达到技术指标。另一方面,SXFEL中的脉冲速调管的输入输出特性存在非线性的关系,这种电子管放大器不理想的非线性特性会导致微波低电平(Low Level Radio Frequency,LLRF)控制系统调节的效率降低。基于SXFEL装置,采用基于现场可编程门阵列(Field Programmable Gate Array,FPGA)的数字预失真方法,在LLRF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。S波段加速装置和其相应的东芝E3730A速调管及高压调制器和低电平系统实地测试结果表明,在LLRF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,提高微波低电平控制系统的精度及准确性。
In the microwave low-level control system in Shanghai Soft X-ray Free-electron Laser (SXFEL), the output signal of each klystron is measured and controlled to ensure the stable operation of the accelerator and Achieve technical indicators. On the other hand, there is a non-linear relationship between the input and output characteristics of the pulse oximeter in the SXFEL. The undesirable nonlinearity of the tube amplifier results in the low level radio frequency (LLRF) control system regulating efficiency reduce. Based on the SXFEL device, a field programmable gate array (FPGA) -based digital predistortion method was used to design an online system for linearization of high-power klystron amplifiers in an LLRF control system. Field test results of S-band accelerators and their corresponding Toshiba E3730A klystron, high-voltage modulator and low-level system show that the on-line system established in the LLRF control system can effectively compensate for the nonlinear problem caused by klystrons and improve Accuracy and accuracy of microwave low level control system.