LHAASO实验高精度时间测量系统研究

发布时间：2018-05-11 18:35

本文选题：宇宙线 + 时间测量　；参考：《清华大学》2014年博士论文

【摘要】：开展宽视场、高灵敏度的伽玛射线巡天观测研究是探索宇宙线起源的重要手段。为此，我国科学家提出在海拔4400m处建设大型高海拔空气簇射观测站（LargeHigh Altitude Air Shower Observatory，LHAASO）。其中平方千米地面探测器阵列（KM2A）需要对簇射粒子的到达时间进行精确的测量，为了获得好于0.5°的宇宙线入射角分辨，要求在宽温环境下保证5635个探测器电子学达到500ps （RMS）的时间测量准确度。在此背景下，本文对LHAASO实验的高精度时间测量系统展开研究。大范围的时间测量系统要求所有节点获得高精度和高准确度的同步时钟。White Rabbit（WR）时钟同步方法基于标准以太网，能够在大范围、多节点的应用环境中实现亚纳秒的时钟同步准确度。本文介绍了WhiteRabbit的基本原理和同步链路模型，对该模型中的关键参数进行了标定和实验验证；着重对White Rabbit同步链路各环节的温度效应展开研究，量化其对时钟同步性能的影响；针对WhiteRabbit设备的硬件延时温度效应，采取了一种在线校正方法；并对不同应用环境下的White Rabbit同步性能进行测试和分析。高精度的时间数字转换器（Time-to-Digital Converter, TDC）是保证各节点时间测量性能的关键因素。本文介绍了基于FPGA进位链的时间数字转换器的基本原理和设计方法，，分析了进位链结构、温度和内核电压等因素对TDC精度的影响，着重对FPGA进位链温度效应的自动校正方法展开研究，在低成本的Cyclone II系列FPGA上完成了多通道的TDC设计，并在宽温范围下取得了优于23p（sRMS）的单次测量精度。基于上述方法研究，本文完成了LHAASO实验高精度时间测量系统的原型设计。针对宇宙线观测实验的应用模式，采用数据与定时链路融合、冗余连接的方式设计了LHAASO时钟分布与数据传输网络结构；采用模块化的方式完成时间测量节点的硬件和功能设计；在不同环境下对时间测量系统的性能进行了测试和分析。根据测试结果可以推算该时间测量系统在40oC温度变化范围以及五级交换机级联结构下的时间测量准确度好于1ns，任一温度下单节点的时间测量精度好于65ps，满足LHAASO-KM2A和大部分宇宙线观测实验的需求。
[Abstract]:It is an important means to explore the origin of cosmic rays to carry out wide field of view and high sensitivity gamma ray survey. Therefore, Chinese scientists have proposed to build a large high altitude air shower observation station at an altitude of 4400m. The square kilometer ground detector array (KM2A) needs to accurately measure the arrival time of the shower particles. In order to obtain a better resolution of the incident angle of cosmic rays than 0.5 掳, It is required to ensure the time measurement accuracy of 5635 detectors in wide temperature environment. Under this background, the high precision time measurement system of LHAASO experiment is studied in this paper. Large-scale time measurement system requires all nodes to obtain high-precision and high-accuracy synchronous clock .White RabbitWR-based clock synchronization method based on standard Ethernet, which can achieve sub-nanosecond clock synchronization accuracy in a wide range and multi-node application environment. In this paper, the basic principle and synchronous link model of WhiteRabbit are introduced, the key parameters of the model are calibrated and verified by experiments, and the temperature effect of each link of White Rabbit synchronous link is studied to quantify its influence on the performance of clock synchronization. Aiming at the hardware delay temperature effect of WhiteRabbit equipment, an on-line correction method is adopted, and the synchronization performance of White Rabbit in different application environments is tested and analyzed. High-precision time-to-digital converter (TDC) is the key factor to ensure the performance of each node. This paper introduces the basic principle and design method of time digital converter based on FPGA carry chain, and analyzes the influence of carry chain structure, temperature and core voltage on the accuracy of TDC. The automatic correction method of FPGA carry chain temperature effect is studied emphatically. The multi-channel TDC design is completed on the low cost Cyclone II series FPGA, and the single measurement accuracy is better than that of 23pcs RMS in wide temperature range. Based on the above research, the prototype design of high precision time measurement system for LHAASO experiment is completed. Aiming at the application mode of cosmic ray observation experiment, the LHAASO clock distribution and data transmission network structure are designed by data and timing link fusion and redundant connection, and the hardware and function design of time measurement node is accomplished by modularization. The performance of time measurement system is tested and analyzed in different environments. Based on the test results, it can be deduced that the time measurement accuracy of the time measurement system under the 40oC temperature range and the cascade structure of the five-stage switch is better than 1ns, and the time measurement accuracy of any temperature sending order node is better than 65ps. it meets the requirements of LHAASO-KM2A and the order node. The demand for most cosmic ray observation experiments.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P172.4

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