节点文献
北京谱仪（BESIII）飞行时间读出电子学系统设计与实现
【作者】 郭建华；
【作者基本信息】 中国科学技术大学 ， 物理电子学， 2007， 博士
【摘要】 北京正负电子对撞机(BEPC，Beijing Electron Positron Collider)目前是国际上工作在τ-粲能区的唯一高亮度正负电子对撞机。它主要由直线加速器、束流运输线、储存环、北京谱仪(BES，Beijing Spectrometer)和北京同步辐射装置等组成。BEPC自1989年建造投入使用后，在1996年对加速器和探测器均进行了升级，使性能有了相当大的改进。升级后，对撞机仍称为BEPC，而谱仪则称为BESⅡ。但经过几年的运行，BEPC和BESⅡ已经不能满足要求，同时它也存在着老化的问题，所以目前高能物理研究所正进行BEPC和BES的再次升级，升级后的对撞机称为BEPCⅡ，对应的谱仪为BESⅢ。BESⅢ由主漂移室、电磁量能器、飞行时间谱仪和μ子计数器等组成。其中飞行时间谱仪TOF(time-of-flight)是用来测量带电粒子飞行时间的探测器，其主要功能是通过所测量的飞行时间信息，结合主漂移室测得粒子的动量和径迹，从而辨别粒子的种类。TOF分桶部和端部两个部分。作为BES升级的一部分，BESⅢ的飞行时间计数器精度将得到大幅度的提高(桶部的探测精度由180ps提高到90ps，端盖由350ps提高到110ps)，其中要求TOF读出电子学系统(Readout System)的时间测量精度好于25ps。本论文将讨论BESⅢ飞行时间读出电子学系统，特别是其中的前端电子学模块(FEE Module，Front End ElectronicModule)，所涉及到的各种技术以及设计和实现细节。通常对模拟信号的时间测量由定时甄别和时间数字转换构成。本文的第二章介绍了前沿定时、过零定时、恒比定时和ARC定时的特点。其中前沿定时和恒比定时是物理实验常用的两种定时方式。前沿定时结构简单，但需要做“时间游动”修正，常见的修正方法有幅度修正、电荷修正、波形数字化等。恒比定时虽然能够消除幅度对定时的影响，但其结构相对比较复杂。定时后的信号送入时间数字化TDC芯片中进行量化。第三章详细介绍了TDC的一些技术指标和常见的架构。通常TDC实现的方法除了使用计数器直接量化外，还可以先将其转化为幅度、距离等物理量后再量化，不过对于绝对的时间测量一般都采用计数器法。计数器法结构简单、容易集成，将它结合时间内插技术可以获得高精度的全数字化TDC。第三章的最后部分介绍了欧洲核子中心开发的高性能全数字化TDC：HPTDC。第四章到第六章主要围绕BESⅢ飞行时间谱仪读出电子学系统的设计、实现和测试展开讨论。第四章首先介绍了国际上几个探测系统的TOF读出电子学系统，如LHC的Alice TOF、KEK的Belle TOF、费米实验室的CDF TOF、布鲁海文实验室的STAR TOF。BESⅢ的TOF读出电子学系统在借鉴这些系统的电子学的基础上，结合自身的特点，提出了前沿定时和利用电荷测量修正“时间游动”效应的方案。电荷测量采用了先将电荷转换为时间宽度再量化的方式，这样定时后的时间量化和电荷测量的量化都可以采用统一的量化器：HPTDC，从而大大简化了设计。第五章介绍了TOF读出电子学系统的设计。TOF读出电子学系统包括了前放和VME机箱系统，其中VME机箱系统中由以下几个部分组成：负责测量时间和电荷的前端电子学读出模块(FEE Module)、负责41MHz的系统时钟扇出的时钟扇出模块(Clock Fanout Module)、负责机箱各FEE模块控制和状态读出的快控制模块(FEE FCtrl Module)、负责发送TOF快时间响应信号的后插模块(FEE Rear Module)。本章着重介绍了TOF前端电子学FEE模块的实现细节。第六章介绍读出电子学系统的测试。测试主要针对前端电子学模块的时间测量和电荷测量两个方面性能，分为三个阶段：实验室环境下的电子学测试、实验室环境下宇宙线测试和束流环境下的测试。实验室环境下的电子学测试主要利用可编程的信号源模拟光电倍增管的信号。输入到前端电子学模块中测量时间精度、电荷精度(线性、噪声误差等)、温漂影响等。宇宙线测试是利用探测器系统搭建的望远镜系统测试宇宙射线下的前端电子学时间测量精度。而束流实验是为了验证在加速器的恶劣环境下，多种不同粒子束(质子、电子等)击中闪烁体时前端电子学的测量精度。所有的测试都表明，设计的TOF读出电子学系统能够达到25ps的测量精度，能够满足BESⅢ对TOF的要求。
【Abstract】 The Beijing Electron Positron Collider (BEPC) was built in 1989 and its research field covers Tau physics, Charm physics and the precise research of standard model. BPEC consists of the injector, the storage ring, the transportation line, the Beijing Spectrometer (BES), the Beijing Synchrotron Radiation Facility (BSRF), etc.There has been an upgrade in 1996 for BEPC, and the BEPC/BES are called BEPC/BESII afterward. To improving the performance and solving the problem of aging, BEPC will be upgraded again, and the new version of BEPC/BES will be named BEPCII/BESIII.BESIII consists of Main Drift Chamber (MDC), Electromagnetic Calorimeter (EMC), Time-Of-Flight counter (TOF) andμIdentifier, trigger system, etc. The purpose of TOF is to measure the flight time of charged particles. Particle identification is made by comparing the measured time against predicted time obtained from the charged particle track length and momentum given by the Main Drift Chamber. The TOF also provide a fast trigger signal for charged particles, as well as cosmic ray background rejection. The TOF of BESIII contains the barrel part and endcap part. The RMS time resolution of barrel part will be less than 90ps and the endcap part will be less than 110ps. To meet the requirement of BESIII TOF, the Readout System of TOF, consists of the front end electronic (FEE) and Readout Electronic, will contribute less than 25ps RMS uncertainty. This thesis mainly discusses the detail of the implement of BESIII TOF Readout electronic system.Normally, time measure is including time discrimination and time to digital converter (TDC). In the chapter 2, we discuss the characteristic of leading end discriminator, zero crossing discriminator and constant faction discriminator (CDF) and ARC discriminator. Leading end discriminator and CDF discriminator are widely used in high energy experiment. The advantage of leading end discriminator is its simple structure, easy to realized and integrated. But it has timing error because of’time walk’ effect. So the result of leading end discriminator needs to be corrected by charge measurement or amplitude measurement, etc. CDF discriminator can eliminate ’time walk’ effect, but it is more complicated.In chapter3, some types of TDC are introduced, such as using counter method, TAC+ADC method, and delay chain method. Counter type is the most common technique for time measurement. It is full digital and very simply. But the time resolution of counter type TDC is not very good (about 1ns) because of the frequency of counter. More precise counter type TDC can be implemented by delay chain interpolation technique. Using this technique, CERN has developed a high resolution TDC, named HPTDC.In chapter 4 to chapter 6, the design and test of BESIII TOF Readout Electronic System are discussed. In chapter 4, we introduce some particle collider’s TOF electronic, such as BELLE TOF in KEK, ALICE TOF in LHC, CDF TOF in Femi lab, STAR TOF in BNL. Based on the study of these electronics design’s principle and the characteristic of BESIII TOF detector, the BESIII TOF Readout Electronic System develops a practical scheme: using leading end discriminator and HPTDC to measurement flight time, and using QTC circuit and HPTDC to measure the charge of the hit signal.In chapter 5, the detail of TOF Readout Electronic System is introduced. It includes Pre_Amplifier and other electronic modules in VME crate. They consist of 14 FEE (Front End Electronic) modules, 1 FEE clock fanout module and 1 FEE fast control module. The function of FEE module is measure the flight time and charge of the coming hit signal. The clock fanout module is responsible for the 41.65Mhz system clock of all modules. And FEE fast control module will receive the control signal (such as L1 trigger) from global trigger system and send the status signal of FEE readout module as well.In chapter 6, we will introduce the test result of TOF electronic, such as time and charge measurement performance. The process of test is including electronic test using signal generator, cosmic test using telescope system and beam test using the LINAC of BEPC in IHEP. All the test result shows that the performance of TOF Readout Electronic System can meet the requirement of BESIII TOF.