【作者】 尹春艳；

【导师】 刘树彬；

【作者基本信息】 中国科学技术大学 ， 物理电子学， 2011， 硕士

【摘要】 北京正负电子对撞机(BEPC)和北京谱仪(BESⅢ)于2008年7月成功升级,升级后系统分别称为BEPCII和BESⅢ。作为对撞机的核心部分之一,北京谱仪BESⅢ担负着测量和分辨对撞机产生的粒子任务,由主漂移室,飞行时间计数器(TOF),μ子计数器,以及对应的读出电子学系统等组成。自升级后运行以来,各项指标均满足设计要求,取得一系列重大成果。飞行时间计数器(TOF)是BESⅢ实现粒子分辨的重要部分,测量带电粒子飞行时间,分为端盖(ETOF)和桶部(BTOF)两部分,其中BTOF是世界上同类TOF探测器中性能最好的,时间测量精度小于90ps。但ETOF由于1)物质层散射增加了端盖径迹长度的不确定性;2)MDC径迹重建导致Z向击中位置不确定;3)受到噪声问题的困扰,导致ETOF测量精度仅138ps。为实现更高的时间分辨和提高粒子分辨能力,ETOF系统将升级,包括探测器和读出电子学系统。升级后的系统探测器将使用MRPC技术,具有高时间分辨精度和探测效率,并在国际大型粒子物理装置,如CERN的ALICE TOF系统和美国BNL的STAR TOF系统中成功运用。根据MRPC探测器输出特点,飞行时间读出电子学系统也将升级,以实现高精度的飞行时间测量,测量精度要求小于25ps。本文将讨论ETOF升级读出电子学系统实现方案,重点介绍时间测量的实现方法和升级系统中采用的方案、时间数字化插件(TDIG,Time Digital)的设计和测试结果。粒子物理实验中,飞行时间测量通常对探测器输出信号定时甄别,再经时间数字化实现。第二章介绍时间测量方法,详细阐述被广泛采用的前沿定时和计数器型时间数字化技术,引入高性能TDC——HPTDC的介绍。由于前沿定时需要修正“时间游动”效应,常用的方法有电荷修正,幅度修正等。其中电荷修正方法在大型探测器系统中被采用,实现的前提是对信号进行电荷测量。第二章中介绍电荷测量技术,如波形采样,电荷-电压转换和电荷-时间转换等。详细说明通过测量时间实现的电荷-时间转换和基于这个方法的TOT技术。第三章调研国内外大型探测器系统读出电子学,结合ETOF升级探测器自身的特点,提出了基于TOT技术的放大甄别和基于计数器TDC的时间数字化方案,并采用电荷修正方法修正“时间游动”效应。时间测量和电荷测量数字化均由HPTDC芯片实现。第四章讨论整个读出电子学系统设计,包括实现探测器信号放大甄别的前端电子学模块FEE,时间数字化的TDIG插件和辅助模块CTTP,主时钟扇出模块。重点阐述时间数字化TDIG插件的设计和技术细节。第五章展示读出电子学系统的性能测试结果。测试在实验室环境下进行,分为时间数字化TDIG插件性能测试和读出电子学系统性能测试两个阶段。主要测试各个通道的测量精度和非线性。测试结果表明,读出电子学系统满足设计指标,实现小于25ps的测量精度。更多还原

【Abstract】 The Beijing Electron Positron Collider (BEPC) and the Beijing Spectrometer (BES) have been upgraded since July, 2008. The systems are named BEPC II and BESⅢrespectively.As the major part of the BEPCⅡ, the BESⅢincludes a drift chamber, a time-of-flight system and a muon identifier system and so on. Its function is to measure and identify a substantial fraction of the particles (PID) produced by the BEPC II. Since the accomplishment of upgrading, BESⅢhas obtained a serial of great achievement.One part of BESⅢ, time-of-flight system (TOF) measures the relative arrival time of particle generated by the electron-position collisions in the BEPC II. The TOF system is divided into two parts: the end-cap TOF (ETOF) and the barrel TOF (BTOF). The time resolution of BTOF is less than 90ps, which means it is the best TOF detector using PMT as the detector in the world. However, the time resolution of the ETOF is more than 138ps, which because of the influence of noise in the system and some other reason which increases the uncertainty of the particle’s information generated by the detector.In order to increase the capability of PID and the time resolution of ETOF, the ETOF improvement has been proposed and the whole projected is under design. In the upgrading system, MRPC is used as the detector. This detector has some advantages, such as the high time resolution and efficiency. It has been used in ALICE TOF in LHC and STAR TOF in BNL successfully. To meet the demand of improvement of ETOF, the readout electronics system is also improved and achieves time measurement with high resolution (RMS < 25ps).This thesis discusses the implement of the readout electronics system and mainly discusses the method to achieve time measurement, as well as the technology used in the system.In the physics experiment, the time-of-flight measurement consists of time discrimination and time-to-digital converter (TDC). The method of time measurement will be discussed in the chapter 2. We discuss the leading-end discrimination and counter type TDC. The characteristic of a typical TDC-HPTDC is mentioned in the chapter, too. In the step of discriminating, we need to correct the error caused by“time walk”effect, such as the method of charge correcting and amplitude correcting. Currently, the method of charge correcting has been implemented and the charge measurement is required. The typical charge measurement is wave sampling, charge-to-time conversion and charge–to-voltage conversion. The time-over-threshold (TOT) technique is based on charge–to-time converter is introduced in the chapter, too.In chapter 3, some particle collider’s readout electronics systems are introduced. Considering the feature of the MRPC used in the upgrading ETOF, we proposed a practical scheme: using TOT to accomplish signal amplification and time discrimination and counter type TDC to digitalize time. The“time walk”effect correction is implemented by charge correcting. Both time measurement and charge measurement can be achieved by HPTDC.In chapter 4, we discuss the design of the whole electronics system. The system includes the front-end electronics module (FEE), the time-to-digital module (TDIG), the auxiliary module (CTTP), and the clock module. We mainly discuss the scheme of the TDIG module and some detail.In chapter 5, we introduce the test result of readout electronics, using signal generator. We test the time resolution and INL of each channel of TDIG module, as well as the whole readout electronics. The result shows the readout electronics system meets the demand of ETOF upgrading.更多还原