GPU并行过滤LHAASO-WCDA本底噪声

针对LHAASO-WCDA的高噪声率,开发了基于GPU的在线噪声过滤方法。该方法利用Nvidia公司的CUDA技术通过对天区的并行扫描,筛选出最可几天区再经过后续处理从而实现在线噪声过滤与数据压缩。实验测试结果表明:与传统CPU串行相比采用GPU的多线程并行处理后程序运行效率得到十倍以上的提升。通过该方法,相对较小规模的GPU服务器可代替大型的CPU集群,同时可以加强WCDA对瞬态源的监测。

WCDA动态范围扩展系统快速模拟研究

现代物理学中,超高能γ天文已成为天体物理学的主要分支之一。针对超高能宇宙线事例模拟的困难,本文进行了WCDA动态范围扩展系统快速模拟的研究,主要包括对光子数薄化处理和参数化模拟两种方法。这两种方法可以运用到WCDA动态范围扩展系统中,用来快速高效模拟高能量宇宙线事例在探测器上的响应。

基于嵌入式系统的LHAASO WCDA中TCP/IP数据传输接口设计

针对大型高海拔空气簇射观测站水切伦科夫探测器阵列,开展了前端电子学数据传输接口设计。基于实验数据率大、数据可靠性要求高的特点,进行了千兆以太网下的TCP/IP数据传输模块的设计。本文主要介绍了基于FPGA嵌入式系统的TCP/IP数据传输技术在LHAASO WCDA中的应用研究。实验结果表明:此数据传输模块数据率可达237 Mbps,满足应用要求。同时,还对此模块进行了24小时的传输测试,数据传输率保持稳定。

中国电建成都院EPC工程——高海拔宇宙线观测站WCDA1号水池开始充水闭水试验

7月27日19时27分,随着指挥长指令下达,由中国电建集团成都勘测设计研究院EPC总承包的高海拔宇宙线观测站（LHAASO） WCDA1号水池开始充水闭水试验。次日15时9分,达到第一阶段充水深度,随之安装的2台WCDA探测器运转正常,标志着LHAASO主体工程WCDA1号水池即将交付科学探测实验。

高原极端气候下水切伦科夫(WCDA)水池防冻控制保温设计

针对高原极端气候下水切伦科夫(WCDA)水池热湿安全与外保温设计开展了研究,对冻土沼泽区水池围护结构的热过程进行了数值分析,提出了水池防冻外保温系统的安全设计策略,并通过现场实测予以证实。

A dynamic range extension system for LHAASOWCDA-1

Purpose The main scientific goal of LHAASO-WCDA is to survey gamma-ray sources with energy from 100 GeV to 30 TeV.To observe high-energy shower events,especially to measure the energy spectrum of cosmic rays from 100 TeV to 10 PeV,a dynamic range extension system(WCDA++)is designed to use a 1.5-inch PMT with a dynamic range of four orders of magnitude for each cell in WCDA-1.Method The dynamic range is extended by using these PMTs to measure the effective charge density in the core region of air shower events,which is an important parameter for identifying the composition of primary particles.Result and Conclusion The system has been running for more than one year.In this paper,the details of the design and performance of WCDA++are presented.

LHAASO WCDA前端芯片批量测试系统的设计

LHAASO(Large High Altitude Air Shower Observatory)WCDA(Water Cerenkov Detector Array)要求其读出电子学实现大动态范围下精确的时间和电荷测量,为此设计了一款前端读出芯片PASC(PreAmplifier and Shaping Circuit)ASIC(Application Specific Integrated Circuit),即将用于LHAASO WCDA第三水池的读出。为了满足对此芯片大批量测试需求,设计了此ASIC测试系统,实现了对芯片时间和电荷性能的自动化测试。在介绍此芯片基本工作原理的基础上,讨论了测试系统的设计方案和基本结构,包括硬件电路设计和自动化测试软件设计。该测试系统已应用于LHAASO工程项目的芯片筛选并且已完成了100片芯片的测试工作,能够通过中央控制软件,与多台仪器通讯,进行仪器控制,完成自动化测试和数据记录。这一自动化测试方法,更适用于大动态范围下、高精度读出芯片的性能测试和评估,大大简化测试流程,尤其能够大幅提升批量测试中大量重复性测试步骤的工作效率。文中展示了基于此测试系统已完成的100片芯片的测试结果,结果表明,芯片各项性能参数满足LHAASO第三水池工程应用需求。

Proposal of the readout electronics for the WCDA in the LHAASO experiment

The LHAASO （Large High Altitude Air Shower Observatory） experiment is proposed for a very high energy gamma ray source survey, in which the WCDA （Water Cherellkov Detector Array） is one of the major coinponents. In the WCDA, a total of 3600 PMTs are placed under water in four ponds, each with a size of 150m×150 m. Precise time and cimrge measurement is required for the PMT signals, over a large signal amplitude range from a single P.E. （photo electron） to 4000 P.E. To fulfill the high requirement of a signal measurement in so many front end nodes scattered in a large area, special techniques are developed, such as multiple gain readout, hybrid transmission of clocks, commands and data, precise clock phase alignment and new trigger electronics. We present the readout electronics architecture for the WCDA and several prototype modules, which are now being testedin the laboratory.

A method to monitor and measure the water transparency in LHAASO-WCDA using cosmic muon signals

The Large High Altitude Air Shower Observatory（LHAASO） is to be built at Daocheng, Sichuan Province, China. As one of the major components of the LHAASO project, a Water Cherenkov Detector Array（WCDA）, with an area of 78000 m^2, contains 350000 tons of purified water. The water transparency and its stability are critical for successful long-term operation of this project. To gain full knowledge of the water Cherenkov technique and investigate the engineering issues, a 9-cell detector array has been built at the Yangbajing site, Tibet, China. With the help of the distribution of single cosmic muon signals, the monitoring and measurement of water transparency are studied. The results show that a precision of several percent can be obtained for the attenuation length measurement,which satisfies the requirements of the experiment. In the near future, this method could be applied to the LHAASOWCDA project.

Analog front-end prototype electronics for the LHAASO WCDA

In the readout electronics of the Water Cerenkov Detector Array （WCDA） in the Large High Altitude Air Shower Observatory （LHAASO） experiment, both high-resolution charge and time measurement are required over a dynamic range from 1 photoelectron （P.E.） to 4000 P.E. The Analog Front-end （AFE） circuit is one of the crucial parts in the readout electronics. We designed and optimized a prototype of the AFE through parameter calculation and circuit simulation~ and conducted initial electronics tests on this prototype to evaluate its performance. Test results indicate that the charge resolution is better than 1%@4000 P.E. and remains better than 10%@1 P.E., and the time resolution is better than 0.5 ns RMS, which is better than the application requirements.

Design of the photomultiplier tube bases for high dynamic range readout in WCDA

The photomultiplier tube （PMT） used in the water Cherenkov detector array （WCDA） of the Large High Altitude Air Shower Observatory （LHAASO） requires a good single photoelectron （SPE） spectrum and a charge dynamic range from 1 to 4000 photoelectrons. In this paper, the bases design and improvement of the photomultiplier tube R5912 are presented. The results show that at the gain of 2.6 × 10~6 , the anode output has a good single photoelectron spectrum, and its charge non-linearity is within 5% when the number of photoelectrons （nPE） is 3500. The charge non-linearity of the 8th dynode output is within 2% when the number of nPE is 4000, which satisfies the dynamic range requirement.

Line-of-shower trigger method to lower energy threshold for GRB detection using LHAASO-WCDA

Purpose Observation of high energy and very high emission from Gamma Ray Bursts(GRBs)is crucial to study the gigantic explosion and the underline processes.With a large field-of-view and almost full duty cycle,the Water Cherenkov Detector Array(WCDA),a sub-array of the Large High Altitude Air Shower Observatory(LHAASO),is appropriate to monitor the very high energy emission from unpredictable transients such as GRBs.Method Nevertheless,the main issue for an extensive air shower array is the high energy threshold which limits the horizon of the detector.To address this issue a new trigger method is developed in this article to lower the energy threshold of WCDA for GRB observation.Result The proposed method significantly improves the detection efficiency of WCDA for gamma-rays around the GRB direction at 10-300 GeV.The sensitivity of the WCDA for GRB detection with the new trigger method is estimated.The achieved sensitivity of the quarter WCDA array above 10 GeV is comparable with that of Fermi-LAT.The data analysis process and corresponding fluence upper limit for GRB 190719C is presented as an example.

Online charge calibration of LHAASO-WCDA——a study with the engineering array

LHAASO-WCDA is a large ground-based water Cherenkov detector array planned to be built at ShangriLa, Yunnan Province, China. As a major component of the LHAASO project, the main purpose of LHAASO-WCDA is to survey the northern sky for very-high-energy（above 100 GeV） gamma ray sources and measure the spectrum. To gain full knowledge of the water Cherenkov technique and to investigate the engineering issues, a 9-cell detector array has been built at the Yang-Ba-Jing site, neighboring the ARGO-YBJ experiment. With the array, charge calibration methods for both low and high ranges of the PMT readout are studied, whose result shows that a precision at several percentages can be reached, which can satisfy the requirement of the detector array. During the long term operation, the charge calibration stability and environmental afection are studied; in this paper, the results are discussed. These calibration methods are proposed to be applied in the future LHAASO-WCDA project.

LHAASO水切伦科夫探测器阵列时钟原型系统

介绍了LHAASO WCDA读出电子学时钟原型系统的设计,分析了该时钟系统的设计原理,介绍了测试方法和测试结果。该原型系统基于精简的White Rabbit Project原理设计,主要包括时钟源插件、时钟发送插件和时钟接收模块3部分。对该原型系统的测试结果表明,时钟接收模块上两时钟通道之间的时钟偏差可以调整到<80 ps,时钟抖动<40 ps,可满足LHAASO WCDA读出电子学设计需求。

An analogue front-end ASIC prototype designed for PMT signal readout

The Water Cherenkov Detector Array （WCDA） is one of the core detectors in the Large High Altitude Air Shower Observatory （LHAASO）, and it consists of 3600 photomultiplier tubes （PMTs）. Both high resolution time and charge measurement are required over a large dynamic range from 1 photoelectron （P.E.） to 4000 P.E. The prototype of an analogue front-end Application Specific Integrated Circuit （ASIC） fabricated using Global Foundry 0.35 μm CMOS technology is designed to read out the PMT signal in the WCDA. This ASIC employs leading edge discrimination and an （RC）4 shaping structure. Combined with the following Time-to-Digital Converter （TDC） and Analog-to-Digital Converter （ADC）, both the arrival time and charge of the PMT signal can be measured. Initial test results indicate that time resolution is better than 350 ps and charge resolution is better than 10% at 1 P.E. and better than 1% with large input signals （300 P.E. to 4000 P.E.）. Besides, this ASIC has a good channel-to-channel isolation of more than 84 dB and the temperature dependency of charge measurement is less than 5% in the range 0 50℃.

Evaluation of a front-end ASIC for the readout of PMTs over a large dynamic range

The Large High Altitude Air Shower Observatory （LHAASO） project has been proposed for the survey and study of cosmic rays. In the LHAASO project, the Water Cherenkov Detector Array （WCDA） is one of the major detectors for searching for gamma ray sources. A Charge-to-Time Convertor （QTC） ASIC （Application Specification Integrated Circuit）, fabricated with GlobM Foundry 0.35 μm CMOS technology, has been developed for readout of photomultiplier tubes （PMTs） in the WCDA. This ASIC provides both time and charge measurement of PMT signals. The input charge is converted to a pulse width based on the Time-Over-Threshold （TOT） technique and linear discharge method; as for time measurement, leading edge discrimination is employed. This paper focuses on the evaluation of this front-end readout ASIC performance. Test results indicate that the time resolution is better than 400 ps and the charge resolution is better than 1% with large input signals and remains better than 15% @1 photoelectron （P.E.）, both beyond the application requirement. Moreover, this ASIC has a weak ambient temperature dependence, low input rate dependence and high channel-to-channel isolation.

Design and simulation of a 12-bit,40 MSPS asynchronous SAR ADC for the readout of PMT signals

High precision and large dynamic range measurement ave required in the readout systems for the Water Cherenkov Detector Array （WCDA） in the Large High Altitude Air Shower Observatory （LHAASO）. This paper presents a prototype of a 12-bit 40 MSPS Analog-to-Digital Converter （ADC） Application Specific Integrated Circuit （ASIC） designed for the readout of the LHAASO WCDA. Combining this ADC and the front-end ASIC finished in our previous work, high precision charge measurement can be achieved based on the digital peak detection method. This ADC is implemented based on a power-efficient Successive Approximation Register （SAR） architecture, which incorporates key parts such as a Capacitive Digital-to-Analog Converter （CDAC）, dynamic compavator and asyn- chronous SAR control logic. The simulation results indicate that the Effective Number Of Bits （ENOB） with a sampling rate of 40 MSPS is better than 10 bits in an input frequency range below 20 MHz, while its core power consumption is 6.6 mW per channel. The above results are good enough for the readout requirements of the WCDA.

Study on the optimization of the water Cherenkov detector array of the LHAASO project for surveying VHE gamma ray sources

It is prpopsed that a water Cherenkov detector array, LHAASO-WCDA, is to be built at Shangri-la, Yunnan Province, China. As one of the major components of the LHAASO project, the main purpose of it is to survey the northern sky for gamma ray sources in the energy range of 100 GeV-30 TeV. In order to design the water Cherenkov array efficiently to economize the budget, a Monte Carlo simulation is carried out. With the help of the simulation, the cost performance of different configurations of the array are obtained and compared with each other, serving as a guide for the more detailed design of the experiment in the next step.