LHAASO WCDA光电倍增管大动态范围读出研究

发布时间：2018-05-20 19:59

本文选题：宇宙线 + 大型高海拔空气簇射观测站　；参考：《中国科学技术大学》2014年博士论文

【摘要】：宇宙线自发现以来就成为了人类探索宇宙的重要媒介。在过去的100多年的时间中,科学家逐渐了解了宇宙线的许多信息,包括宇宙线的成分、能谱等,但宇宙线仍然存在着许多未解之谜。寻找宇宙线的起源是宇宙线物理的核心问题。为了探索和研究这一问题,我国科学家提出了在我国的高海拔地区建设一个大型的宇宙线观测站——大型高海拔空气簇射观测站(Large High Altitude Air Shower Observatory,LHAASO)。 LHAASO的核心科学目标是探索高能宇宙线起源,研究相关天体演化和暗物质等。LHAASO由四个探测器阵列组成,包括占地一平方公里的粒子簇射地面阵列(Kilometer-square Array, KM2A)、水切伦科夫探测器阵列(Water Cherenkov Detector Array,WCDA)、广角切伦科夫望远镜阵列(Wide Field of View Cherenkov Telescope Array,WFCTA)、簇射芯探测器(Shower Core Detector Array, SCDA)。 WCDA是LHAASO的重要组成部分,其探测目标是巡天扫描北半球的甚高能1,射线源。WCDA的总面积达到90000平方米,由四个同样大小的水池组成。每个水池被分成了900路5m×5m的单元探测器。每单元探测器需要一支八英寸半球形光电倍增管,光阴极朝上,用于记录水中产生的切伦科夫光的电荷和时间信息。物理模拟结果表明WCDA信号读出要求满足的性能指标包括：信号增益约为2.5×106,单光电子谱的峰谷比2.0,暗噪声计数率5kHz,信号上升时间4ns,渡越时间分散4ns,线性动态范围达到1-4000光电子。 LHAASO WCDA研制的关键问题是要解决光电倍增管的大动态读出性能,难度在于在较高的增益水平下,必须保持很大的线性动态范围,同时还需要具备良好的单光电子分辨能力以及时间性能。由于常规的PMT信号读出设计方案很难同时满足这些需求,因此需要研究如何改进和优化光电倍增管的分压及读出电路。论文首先对宇宙线物理进行了论述,包括宇宙线的成分、能谱、起源、传播和加速机制、探测手段等。详细调研了国内外一些大型的水切伦科夫探测器,以及这些探测器所使用的光电倍增管的性能指标。详细的论述了水切伦科夫探测器和WCDA的工作机制以及实验要求。论文研究的主要课题是针对WCDA的具体实验要求,对大面积光电倍增管(Hamamatsu R5912)的读出电路进行设计和改进,并通过大量的实验研究提出一种满足WCDA实验要求的PMT分压和信号读出设计方案。测试的结果表明,在1000V的工作电压下,光电倍增管的增益能够达到2.5×106,单光电子谱的峰谷比为2.4,脉冲信号上升时间约为4ns,单光子渡越时间分散为3.67ns,暗噪声计数率在工作增益下为l kHz左右,阳极和第十打拿极的线性动态范围最大能够达到3500个光电子,第八打拿极的线性动态范围能够达到6000个光电子以上,这是R5912首次在该增益下能够达到如此大的线性动态范围,解决了WCDA研制和PMT读出设计的关键问题。文中详细论述了这些性能参数的具体测试方法,以及为开展此项研究,所建立的PMT性能测试系统。由于WCDA有3600路单元探测器,因而一共有3600个光电倍增管需要进行性能测试。因此,需要建立起一套装置以实现批量测试。我们在单个PMT性能测试基础上,完成批量测试装置研究。该测试装置包括暗箱、分光器、光纤、电子学、数据获取系统等。该装置进行测试结果显示,其避光性、电磁屏蔽能力、分光均匀性,以及电子学和数据获取系统工作正常,各项性能能够满足批量测试的需求。研究结果为LHAASO立项及WCDA工程设计提供重要的数据,为下一步研究奠定了必要的基础。
[Abstract]:Since the discovery of the cosmic ray has become an important medium for human exploration of the universe. Over the past 100 years, scientists have gradually learned a lot of information about the cosmic ray, including the composition and spectrum of the cosmic rays, but there are still many unsolved mysteries in the cosmic ray.
Looking for the origin of cosmic rays is the core of cosmic ray physics. In order to explore and study this problem, Chinese scientists have proposed to build a large cosmic ray observatory at high altitude in our country, the large high altitude air shower observation station (Large High Altitude Air Shower Observatory, LHAASO). The core science of LHAASO. The goal is to explore the origin of the high-energy cosmic ray, and to study the evolution of the celestial bodies and the dark matter, such as the.LHAASO consists of four detector arrays, including the Kilometer-square Array (KM2A), the water Cherenkov detector array (Water Cherenkov Detector Array, WCDA), and the wide angle Cherenkov array. Column (Wide Field of View Cherenkov Telescope Array, WFCTA), shower core detector (Shower Core Detector Array, *).
WCDA is an important part of LHAASO. Its detection target is very high energy 1 in the northern hemisphere, the total area of the ray source.WCDA is 90000 square meters, and it is composed of four same sized pools. Each pool is divided into 900 5m x 5m unit detectors. Each unit detector needs a eight inch hemispherical photomultiplier. It is used to record the charge and time information of the Cherenkov light produced in the water. The physical simulation results show that the performance indexes of the WCDA signal readout include: the signal gain is about 2.5 x 106, the peak to valley ratio of the single photoelectron spectrum is 2, the dark noise counting rate is 5kHz, the signal rise time is 4ns, the crossing time dispersing 4ns, the linear dynamic range is reached. To 1-4000 photoelectrons.
The key problem of the development of LHAASO WCDA is to solve the large dynamic readout performance of the photomultiplier tube. The difficulty lies in maintaining a large linear dynamic range at a higher gain level, and having a good single photoelectron resolution and time performance. The conventional PMT signal readout design is difficult to meet at the same time. Therefore, it is necessary to study how to improve and optimize the voltage divider and readout circuit of photomultiplier tube.
This paper first discusses the cosmic ray physics, including the composition of the cosmic ray, the energy spectrum, the origin, the propagation and the acceleration mechanism, the detection method, and so on. It investigates some large water Cherenkov detectors at home and abroad, as well as the properties of the photomultiplier tubes used by these detectors. The water Cherenkov detector and WCD are discussed in detail. The working mechanism of A and the requirements of the experiment.
The main topic of this paper is to design and improve the readout circuit of the large area photomultiplier (Hamamatsu R5912) for the specific experimental requirements of WCDA. A design scheme of PMT partial pressure and signal readout to meet the requirements of the WCDA experiment is proposed by a large number of experimental studies. The results of the test show that under the working voltage of 1000V, light is used. The gain of the multiplier tube can reach 2.5 x 106, the peak to valley ratio of the single photoelectron spectrum is 2.4, the pulse signal rise time is about 4ns, the single photon crossing time is 3.67ns, the dark noise counting rate is about L kHz under the working gain, and the maximum linear dynamic range of the anode and tenth hits can reach 3500 photoelectrons and the eighth hits the polar line. The sexual dynamic range can reach 6000 optoelectronics. This is the first time that R5912 can reach such a large linear dynamic range under this gain. It solves the key problem of WCDA development and PMT readout design. The specific testing methods of these performance parameters are discussed in detail, and the PMT performance test system is set up to carry out this research. Unification.
Since WCDA has 3600 unit detectors, a total of 3600 photomultiplier tubes are required to perform performance testing. Therefore, a set of devices is needed to achieve batch testing. On the basis of a single PMT performance test, we complete a batch test device. The test device includes a dark box, a splitter, an optical fiber, a electronics, a data acquisition system. Test results show that the device can avoid light, electromagnetic shielding, optical uniformity, and the electronic and data acquisition system work normally, and the performance can meet the needs of batch testing.
The research results provide important data for LHAASO project and WCDA engineering design, and lay a necessary foundation for further research.
【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】：2014
【分类号】：P172.4

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