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。

Measurement of water quality in LHAASO-WCDA

Introduction The water Cherenkov detector array(WCDA)is an important detector in the Large High Altitude Air Shower Observatory(LHAASO),which is tasked with continuously surveying VHE gamma-rays sky.The WCDA covers an area of 78,000 m2 and contains 350,000 tons of purified water.The water quality and its stability are critical for its performance and long-term operation.Method Light is exponentially attenuated when propagating in water.Water attenuation length can be obtained by comparing light intensities at different optical path lengths,which is the basic principle of direct measurements.Here,a cylindrical device was designed to continuously monitor and measure water quality in the LHAASO-WCDA.Conclusion The systematic error of the cylindrical device was about 4.1%,indicating it is capable of measuring the water attenuation length in WCDA.Furthermore,suspended particle number and turbidity were confirmed as significantly related to the measured attenuation length.

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.

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.

Performance of LHAASO-WCDA and observation of the Crab Nebula as a standard candle

The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard candle.The WCDA-1 achieves a sensitivity of 65 mCU per year,with a statistical threshold of 5 cr.To accomplish this,a 97.7%cosmic-ray background rejection rate around 1 TeV and 99.8%around 6 TeV with an ap proximate photon acceptance of 50%is achieved after applying an algorithm to separate gamma-induced showers.The angular resolution is measured using the Crab Nebula as a point source to be approximately 0.45°at 1 TeV and better than 0.2°above 6 TeV,with a pointing accuracy better than 0.05°.These values all match the design specifications.The energy resolution is found to be 33%for gamma rays around 6 TeV.The spectral energy distribution of the Crab Nebula in the range from 500 GeV to 15.8 TeV is measured and found to be in agreement with the results from other TeV gamma ray observatories.

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。

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。

Trigger and noise filtering algorithms for the LHAASO water Cherenkov detector array

Introduction The Large High Altitude Air Shower Observatory(LHAASO)will be constructed at Mt.Haizishan,Sichuan Province,China.Among several detector components of the LHAASO,the Water Cherenkov Detector Array(WCDA)is of great importance for gamma-ray astronomy from 100 GeV to 30 TeV.The single-channel counting rate of a photo-multiplier tube can reach as high as 30-35 kHz,most of them are background noise hits from the low energy cosmic ray showers,bringing a big challenge on data transferring,data storage and event reconstruction.Methods In this paper,a dedicated trigger scheme and a fast noise filtering method aiming to deal with these high rate background noise hits are introduced.These methods are tested with some Monte Carlo simulation data,showing a fair efficiency in filtering background noise hits,while most of the real shower signals are kept.Conclusion This method is proposed to be applied in a stage of the online processing just after the data are acquired in LHAASO-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.

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.

Prospects for a multi-TeV gamma-ray sky survey with the LHAASO water Cherenkov detector array

The Water Cherenkov Detector Array(WCDA) is a major component of the Large High Altitude Air Shower Array Observatory(LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under construction. WCDA is aimed at the study of TeV γ-rays. In order to evaluate the prospects of searching for TeV γ-ray sources with WCDA, we present a projection of the one-year sensitivity of WCDA to TeV γ-ray sources from TeVCat using an all-sky approach. Out of 128 TeVCat sources observable by WCDA up to a zenith angle of 45°, we estimate that 42 would be detectable in one year of observations at a median energy of 1 TeV. Most of them are Galactic sources, and the extragalactic sources are Active Galactic Nuclei(AGN).

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.

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.

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 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.