非PLL相位平均型参考线原型验证

射频相位参考线是粒子加速器的重要组成部分之一,为射频低电平控制系统(LLRF)、束流诊断系统、定时系统等提供稳定的相位锁定参考信号。为减少远距离传输过程中由环境温度变化导致的射频传输线中的射频相位漂移,多个加速器装置中已经采用射频相位参考线提供射频相位参考,这些相位参考的实现方案主要是基于恒温控制和基于光纤锁相。与这些方案相比,采用相位平均方法不仅可以保持长距离节点之间的相位稳定,而且更易于现场安装与维护。现有的带有锁相环(PLL)的终端短路方式实现相位平均参考线的方案仍有一些节点数量限制等方面的不足,本文对相位平均参考线结构进行了去除PLL的简化设计并进行了验证,以期增加更多的相位分配节点以及降低对射频器件参数的要求。对非PLL的单端输入终端短路相位平均方案与两端输入各节点间互为参考的相位平均方案分别进行了实验测试,结果表明两者的相位RMS精度可以达到0.1°~0.3°。并对不同的相位平均实现方案中相位不稳定的产生原因进行了分析,结果表明,除环境温度外,同轴线缆材质、合成相位与幅度的不平衡合成等也是重要影响因素。

Prototype Verification of Non-PLL Phase Averaging Reference Line

Radio frequency (RF) phase reference line is one of key components in particle accelerator, which can provide phase locked RF reference signal to low-level RF (LLRF) system, beam diagnostic system, timing system or other phase sensitive systems. To reduce phase fluctuations caused by ambient temperature changes in long-distance particle accelerators, phase reference system has been implemented in several accelerator plants. In current phase reference line (PRL) projects, thermal-control based and fibre phase-locked based are mainly implementation methods. Compared with these PRL solutions, the RF phase averaging method has been proven to be able to maintain phase stability between long-distance nodes and it is easier to be applied to installation and maintenance in situ. The method of using phase-locked loop (PLL) phase averaging PRL still has some limitation on nodes quantities. For considering of simplify structure and more nodes can be added and also decreasing requirements for devices, it is necessary to evaluate the phase averaging structure without PLL. The results for the single-end input and the dual-end input structure of non-PLL design show that both structures have the similar accuracy at 0.1° ~ 0.3°, and the results show that the possible reasons of phase instability in different implementation structures, besides ambient temperature, also has the material of coaxial cable, combination phase, imbalanced combination, etc.