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位于四川省稻城的“高海拔宇宙线观测站”(Large High Altitude Air Shower Observatory, LHAASO)现已实现全阵列运行,其大视场和极高的能谱测量精度为寻找100 TeV光子源提供了强有力的保证,并已取得突破性的研究进展[1-2]。LHAASO的角分辨大约是0.3°[3],如果采用视场较小、但空间分辨更好的成像大气切伦科夫望远镜阵列(Imaging Atmospheric Cherenkov Telescopes, IACT)与之互为补充,例如欧洲的成像大气切伦科夫望远镜大型阵列(CTA)计划[4],则可实现对伽马源的内部结构进行精细测量 [5-6],也有助于对LHAASO观测到的超高能伽马源进行认证。在LHAASO实验中共有18台小型IACT,硅光电倍增(Silicon Photomultiplier, SiPM)相机[7]应用得非常成功,但是LHAASO的小型IACT是面向测量宇宙线成分能谱设计的,不是面向伽马天文观测设计的。因此,在国内发展和H.E.S.S.[8],MAGIC[9],CTA等类似的面向伽马天文观测的IACT是必然的趋势。本文以此为背景,针对面向伽马天文观测的IACT中使用SiPM探测器对宇宙线信号进行探测的需求展开研究,其目的为实现SiPM的信号读出,在大动态范围内完成SiPM信号的高精度时间和电荷测量。
IACT对高能粒子在大气层内发生的簇射过程进行观测,不同事件的簇射过程中簇射轴与IACT的距离不同,导致SiPM探测器输出的信号存在形状上的不一致性,图1给出了探测器输出的三类典型形状的波形。基于信号在形状和幅度的不一致性,希望基于波形数字化技术对探测器输出信号进行读出,完整获取该信号的全波形信息。对全波形信息进行数字信号处理,进而获得精确的时间、电荷等信息,从而为物理学实验提供高质量的物理分析数据。本文基于开关电容阵列(Switched Capacitor Array, SCA) 波形数字化技术设计了读出电子学原型,对探测器信号进行高速模拟采样,并配合相对低速的模拟-数字变换器(Analog-to-Digital Converter, ADC) 进行采样电平的量化,从而实现高速波形数字化。这种架构相比于使用高速ADC直接采样,具有功耗和复杂度更低、集成度更高的优势。
读出电子学系统的主要功能有两个:一是测量SiPM探测器输出信号的电荷量,确定高能粒子携带的能量信息;二是记录探测器输出信号到达的时间信息,为重建高能粒子径迹提供参考。
探测器对电子学系统提出的核心指标,如表1所列。
系统指标 性能要求 电荷动态范围
幅度动态范围
电荷测量精度 RMS
时间分辨 RMS5 ~ 8 000 P.E.
1.6 mV ~ 4 V
< 30% @ 5 P.E. & < 3% @ 8 000 P.E.
10 ns
Design and Testing of Cherenkov Telescope Readout Electronics Prototype Based on Switched Capacitor Array
doi: 10.11804/NuclPhysRev.40.2022035
- Received Date: 2022-03-18
- Rev Recd Date: 2022-05-21
- Publish Date: 2023-06-20
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Key words:
- switched capacitor array /
- waveform digitization /
- time measurement /
- charge measurement
Abstract: Aiming at the requirement for cosmic ray detection in Imaging Atmospheric Cherenkov Telescopes(IACT) using silicon photomultiplier(SiPM) detectors, a prototype of readout electronics is designed based on waveform digitization using the Switched Capacitor Array(SCA) ASIC. The prototype is able to read out SiPM detector signals with a wide dynamic range and then calculate the time and charge information of the input signal. The design scheme and structure of the readout electronics prototype are presented in this paper, and a series of tests are conducted to verify its performance. The preliminary results show that the time resolution of the readout system prototype is better than 800 ps RMS within the full dynamic range. The charge resolution is better than 30% at 5 P.E. and is better than 3% at 8 000 P.E.. The test results indicate that the readout system prototype meets the design requirements.
Citation: | Liujiang YAN, Lei ZHAO, Jiajun QIN, Jinliang GU, Xiongbo YAN, Zhenyan LI, Qi AN. Design and Testing of Cherenkov Telescope Readout Electronics Prototype Based on Switched Capacitor Array[J]. Nuclear Physics Review, 2023, 40(2): 221-228. doi: 10.11804/NuclPhysRev.40.2022035 |