LHAASO WCDA读出电子学时钟同步与数据传输研究

发布时间：2018-09-01 20:04

【摘要】：宇宙线是从宇宙空间到达地球的高能粒子,主要成分包括带电粒子,伽玛光子以及中微子。宇宙线起源于各类天体的演化和高能活动,在传播过程中会受到各种星际介质以及电磁场的影响。对宇宙线进行研究可以帮助理解高能粒子的特性,验证粒子理论,甚至发现新粒子。另一方面研究宇宙线及其起源问题可以帮助我们了解宇宙的起源,发展和演化。伽玛光子作为中性粒子,不易受磁场的干扰而改变传播方向。探测伽玛射线是研究宇宙线起源的重要手段,为此我国科学家提出了建设大型高海拔空气簇射观测站(Large High Altitude Air Shower Observatory,LHAASO)的计划。LHAASO海拔四千多米,包含多个子探测器,分别是广角切伦科夫望远镜阵列,μ子探测器,电磁粒子探测器,水切伦科夫探测器阵列(Water Cherenkov Detector Array,WCDA)。其中WCDA包含三个水池,占地约80000平方米,其间分布着3120个光电倍增管(Photomultiplier Tube,PMT)。WCDA读出电子学采用分布式的前端数字化构架,前端电子学模块(Front End Electronic,FEE)在水池上方就近PMT放置,直接对PMT信号进行电荷和时间的测量,完成数字化,此方案避免了长电缆传输带来的衰减,噪声和干扰,减少了高质量长电缆带来的成本。相应地则要求FEE将数据结果经400～500米的距离传输至后端数据获取系统(DataAcquisition,DAQ)。为保证信号长距传输的质量,在WCDA电子学中使用光纤进行信号传输,并将命令、数据和时钟融合在一个光纤上进行混合传输。LHAASO位于高原上,环境恶劣,四季温差较大,电子学及光纤所处环境都无温度控制的条件,考虑到WCDA对于时间测量精度的需求,则要求在大面积空间范围以及变温环境下实现高精度的时钟相位自动同步与对齐,这是WCDA读出电子学的一个关键技术与设计难点。在目前此领域的研究中,White Rabbit(WR)技术是一个比较好的适用于大尺度空间下的时钟同步方法,然而其精度只能保证在亚纳秒水平上,在国内外和本人所在实验室以前的工作中,并未系统解决电子学和光纤路径延时随温度变化情况下的问题,或者提出基于温度传感器实时测试环境温度配合查找表实现相位补偿。本论文旨在系统研究整个时钟传输系统,包括光纤及电子学变温条件下延时的特性,并提出基于延时增量分配方法来实现时钟相位高精度自动相位同步,而无需使用温度传感器等外围器件,简化了系统的复杂度,提升了其可靠性和灵活性。为保证整个系统相位同步的精度,本论文还对FEE调相电路的实现方法展开了研究。此外,WCDA电子学采用无硬件触发的数据获取方式,即FEE需进行全数据读出,然后使用软件对数据进行触发判选,这样可以增加数据分析的灵活性,但相应地对FEE数据传输的速度和可靠性提出了挑战。为此,WCDA读出电子学要求进行TCP/IP协议的高速数据封装。根据整个LHAASO数据及时钟的总体考虑,要求统一使用WR交换机作为时钟及数据的汇总节点,为此,本论文研究中还需要将自定义的时钟相位同步电路、TCP/IP封装逻辑和WR标准相兼容,这也是本论文中的一个重要工作。论文的结构如下:第一章主要介绍了宇宙线研究的历史,现状以及宇宙线探测方法;然后介绍了 LHAASO实验及其科学目标,描述了 WCDA的读出电子学指标和总体架构,特别是对于时钟和数据传输的要求。第二章对一些大规模物理实验中的时钟和数据传输技术进行了调研。这些实验采用的时钟和数据传输技术,为WCDA时钟与数据传输方案提供了很好的参考。第三章主要分为两个部分,第一是高精度时钟相位同步技术的研究,第二是基于TCP/IP的高速数据传输方法的研究。为了满足WCDA读出电子学的要求,需要在大尺度空间范围以及变温环境下实现时钟相位的同步,同时还需要在前端FEE上实现基于TCP/IP的高速数据传输。最后将两者融合到一起,基于同一光纤进融合传输。第四章主要介绍了硬件电子学的实现,对硬件电路以及逻辑功能进行了详细描述。第五章对时钟同步和数据传输电子学系统进行了测试。时钟同步性能测试方面,首先进行了时钟抖动性能的测试,然后分别使用单层及多层WR交换机,在常温与变温两种环境下进行了同步性能测试。在数据传输测试方面,分别进行了单个FEE及多个FEE同时传输的数据率测试以及误码率测试。最后一章总结了本论文的现有工作以及对下一步的工作方向进行了展望。
[Abstract]:Cosmic rays are energetic particles that arrive at Earth from space. The main components of cosmic rays include charged particles, gamma photons and neutrinos. Cosmic rays originate from the evolution and energetic activities of various celestial bodies and are influenced by various interstellar media and electromagnetic fields during their propagation. On the other hand, the study of cosmic rays and their origins can help us understand the origin, development and evolution of the universe. As a neutral particle, gamma photons are not susceptible to the interference of magnetic field to change the direction of propagation. A plan to build a large high altitude air Shower Observatory (LHAASO) has been proposed. The LHAASO is more than 4,000 meters above sea level and consists of several sub-detectors, namely, a wide-angle Cherenkov telescope array, a muon detector, an electromagnetic particle detector, and a water Cherenkov Detecto detector array. WCDA consists of three pools, covering an area of about 80,000 square meters, in which 3120 photomultiplier tubes (PMTs) are distributed. The scheme avoids the attenuation, noise and interference caused by long cable transmission, and reduces the cost of high quality long cable. Accordingly, FEE is required to transmit the data results through a distance of 400-500 meters to the back-end data acquisition system (DAQ). In CDA electronics, optical fibers are used to transmit signals, and commands, data, and clocks are fused into a single fiber for hybrid transmission. LHAASO is located on a plateau with a harsh environment, a large temperature difference in the four seasons, and no temperature control conditions are available for electronics and optical fibers. It is a key technology and design difficulty in WCDA readout electronics to realize high precision clock phase synchronization and alignment in space range and variable temperature environment.White Rabbit (WR) technology is a good clock synchronization method for large scale space,but its precision can only be guaranteed. At the sub-nanosecond level, there is no systematic solution to the problem of electronics and fiber path delay varying with temperature in the previous work at home and abroad and in my laboratory, or the phase compensation based on temperature sensor real-time test environment temperature matching look-up table is proposed. In order to ensure the accuracy of phase synchronization of the whole system, a method based on delayed incremental allocation is proposed to realize high precision automatic phase synchronization without the use of temperature sensors and other peripheral devices. In addition, WCDA electronics uses a data acquisition method without hardware trigger, that is, FEE needs to read out all data, and then use software to trigger the data selection, which can increase the flexibility of data analysis, but the speed and reliability of FEE data transmission are improved accordingly. For this reason, WCDA readout electronics requires high-speed data encapsulation of TCP/IP protocol. According to the overall consideration of LHAASO data and clock, WR switch is required to be used as the aggregation node of clock and data. For this reason, this paper also needs to study the custom clock phase synchronization circuit, TCP/IP encapsulation logic and WR. The structure of this paper is as follows: Chapter 1 mainly introduces the history, current situation and detection methods of cosmic rays; then introduces the LHAASO experiment and its scientific objectives, describes the readout electronics index and overall structure of WCDA, especially for clock and data transmission. Chapter 2 investigates clock and data transmission techniques in some large-scale physical experiments. The clock and data transmission techniques used in these experiments provide a good reference for WCDA clock and data transmission schemes. In order to meet the requirements of WCDA readout electronics, it is necessary to synchronize the clock phase in large-scale space and in variable temperature environment, and to realize high-speed data transmission based on TCP/IP in front-end FEE. Chapter 4 mainly introduces the realization of hardware electronics, and describes the hardware circuit and logic function in detail. Chapter 5 tests the clock synchronization and data transmission electronics system. In the aspect of clock synchronization performance test, the clock jitter performance is tested first, and then the single-layer and multi-layer WR are used to intersect. In the aspect of data transmission test, data rate test and bit error rate test of single FEE and multiple FEEs are carried out respectively. Finally, the existing work of this paper is summarized and the future work direction is prospected.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O572.1

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