用于大规模物理实验的新型亚纳秒时间分布方法研究

Large scale physics experimental facilities and accelerator based systems require more and more accurate timing system for their physics goal.The proposed LHAASO project would require sub-nanosecond timing distribution for thousands of DAQ nodes within its 1 square km range. Since traditional GPS-based time distribution system and special event trigger system faces great challenges in some area, this project proposed a novel timing system design based on Synchronous Ethernet. According to the analysis on specific facility time measurement uncertainties structure, this project would develop an adaptive all-digital phase tracking frequency distribution and time synchronization system including multiple nodes. Time differences between each nodes would be measured and controlled within 1 nanosecond. Meanwhile, all digital scheme of this method enables that all timing node logic and application software could be embedded on a single programmable chip (FPGA),and the data link network itself could be utilized as timing control media, so the sysmtem complexity and cost could be minimized, and the robustness and manageability would be increased.The research would provide a reference design feasibility analysis for timing system of large scale physics experiment and facilities, especially large scale particle detector array observatories.

当前的大规模物理实验及其装置对数据获取和控制过程的时间同步提出了越来越高的要求，例如LHAASO项目拟在1平方公里内同步数千个数据采集节点的时间戳至亚纳秒精度，而传统的基于GPS或专用信号广播机制的定时系统在大尺度分布范围和高精度的定时要求下面临很大挑战。本项目提出了一种新型的基于同步以太网的定时方法，基于物理实验目标和系统各部分测控不确定度模型的综合分析，通过一种基于数据包的全数字相位跟踪自适应频率分布和时间同步机制，实现所有节点之间的频率锁相及亚纳秒时间戳同步。本方法全数字的特性保证了定时控制节点的逻辑和软件应用可以全部在单片可编程器件（FPGA）上实现，并且利用数据传输网络本身作为定时控制的媒介，最大限度的降低系统复杂度和成本，同时提高系统可靠性和可管理性。本项目的研究将可以为大规模物理实验和科学装置、特别是大型探测器阵列天文台的定时系统提供研究参考和可行性实施方案。

当前的大规模宇宙线观测实验在平方公里的范围内，需要在近万个探测节点间建立亚纳秒级别的同步精度，来协同检测入射宇宙线级联簇射的原始方向，同时还需要考虑探测器节点的数据传输，并具备良好的野外环境适应性。本项目发展了一种新型的基于以太网的定时方法，综合运用基于物理层的频率谐振、基于IEEE 1588协议的时间同步和精确的时钟相位差技术，实现节点间的时钟频率同步和亚纳秒的相位对齐，同时具备绝对时间戳的同步；针对野外部署需求，项目对该技术各环节的温度效应进行了详尽研究并发展了补偿机制；利用同步网络的光纤物理介质，同时实现了物理数据和监控信息的传输，极大简化了分布式探测的系统结构。项目成果已经在相关实验中得到了直接采用。