In the Large High Altitude Air Shower Observatory (LHAASO), the Water Cherenkov Detector Array (WCDA) is one of the key parts. The WCDA consists of 3600 Photomultiplier Tubes (PMTs) scattered in a 90000 m2 area, and both high precision time and charge measurements are required over a large dynamic range from 1 to 4000 Photo Electrons (P.E.). To achieve time measurement precision better than 500 ps RMS, high quality clock distribution and automatic phase compensation are needed among the 400 Front End Electronics (FEE) modules. To simplify the readout electronics architecture, clock, data, and commands are transferred simultaneously over 400-meter fibers, while high speed data transfer interface is implemented based on TCP/IP protocol. Design and testing of the readout electronics prototype for WCDA is presented in this paper. Test results indicate that a charge resolution better than 10% RMS @ 1 P.E. and 1% RMS @ 4000 P.E., and a time resolution better than 300 ps RMS are successfully achieved over the whole dynamic range, beyond the application requirement.
The Water Cherenkov Detector Array (WCDA) is one of the major components of the Large High Altitude Air Shower Observatory (LHAASO). In the WCDA, 3600 Photomultiplier Tubes (PMTs) and the Front End Electronics (FEEs) are scattered over a 90000 m2 area, while high precision time measurements (0.5 ns RMS) are required in the readout electronics. To meet this requirement, the clock has to be distributed to the FEEs with high precision. Due to the "triggerless" architecture, high speed data transfer is required based on the TCP/IP protocol. To simplify the readout electronics architecture and be c…
In the readout electronics of the Water Cerenkov Detector Array (WCDA) in the Large High Altitude Air Shower Observatory (LHAASO), both high-resolution charge and time measurement are required over a dynamic range from 1 photoelectron (P.E.) to 4000 P.E. for the PMT signal readout. In this paper, we present our work on the design of time discrimination circuits in LHAASO WCDA, especially on improvement to reduce the circuit dead time. Several approaches were studied through analysis and simulations, and actual circuits were designed and tested in the laboratory to evaluate the performance. Tes…
LHAASO-WCDA is a large ground-based water Cherenkov detector array planned to be built at Shangri-La, Yunnan Province, China. As a major component of LHAASO project, the main purpose of LHAASO-WCDA is to survey the northern sky for very-high-energy (above 100 GeV) gamma ray sources. To gain full knowledge of water Cherenkov technique and to well investigate engineering issues, a 9-cell detector array has been built at Yang-Ba-Jing site, neighboring to the ARGO-YBJ experiment. With the array, charge calibration methods for low and high ranges of the PMT readout are studied, whose result shows t…
The Water Cherenkov Detector Array (WCDA) is one of the key parts in the Large High Altitude Air Shower Observatory (LHAASO). In the WCDA, 3600 Photomultiplier Tubes (PMTs) and the Front End Electronics (FEEs) are scattered within a 90000 m2 area, while a time measurement resolution better than 0.5 ns is required in the readout electronics. To achieve such time measurement precision, high quality clock distribution and synchronization among the 400 FEEs (each FEE for 9 PMTs readout) is required. To simplify the electronics system architecture, data, commands, and clock are transmitted simultan…
The LHAASO (Large High Altitude Air Shower Observatory) experiment is proposed for very high energy gamma ray source survey, in which the WCDA (Water Cherenkov Detector Array) is the one of the major components. In the WCDA, a total of 3600 PMTs are placed under water in four ponds, each with a size of 150 m x 150 m. Precise time and charge measurement is required for the PMT signals, over a large signal amplitude range from single P.E. (photo electron) to 4000 P.E. To fulfill the high requirement of signal measurement in so many front end nodes scattered in a large area, special techniques ar…
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 78,000~$\rm m^{2}$, contains 350,000~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 sin…
The water Cherenkov detector array (WCDA) is one of the key detectors in the large high altitude air shower observatory (LHAASO), which is proposed for very high gamma ray source survey. In WCDA, there are more than 3000 photomultiplier tubes (PMTs) scattered under water in an area of 80000 m2. As for the WCDA readout electronics, both high precision time and charge measurement is required over a large dynamic range from 1 photon electron (P.E.) to 4000 P.E. To reduce the electronics complexity and improve the system reliability, a readout scheme based on application specific integrated circui…
Time and charge measurements over a large dynamic range from 1 Photo Electron (P.E.) to 4000 P.E. are required for the Water Cherenkov Detector Array (WCDA), which is one of the key components in the Large High Altitude Air Shower Observatory (LHAASO). To simplify the circuit structure of the readout electronics, a front end ASIC was designed. Based on the charge-to-time conversion method, the output pulse width of the ASIC corresponds to the input signal charge information while time information of the input signal is picked off through a discriminator, and thus the time and charge informatio…
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 whole 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 resolutio…
The first Water Cherenkov detector of the LHAASO experiment (WCDA-1) has been operating since April, 2019. The first 10 months of data have been analyzed to test its performance by observing the Crab Nebula as a standard candle. The WCDA-1 achieves the sensitivity of 65 mCU per year with a statistical threshold of 5 $σ$. In order to do so, 97.7\% cosmic ray background rejection rate around 1 TeV and 99.8\% around 6 TeV with an approximately photon acceptance about 50\% by using the $compactness$ of the shower footprints to be greater than 10 as the discriminator between gamma induced showers a…
The Large High-Altitude Air Shower Observatory (LHAASO) is being built at Haizi mountain, Sichuan, China at an altitude of 4410 m. One of its main goals is to survey the northern sky for very-high-energy (above 100 GeV) gamma ray sources via its ground-based Water Cherenkov Detector Array (WCDA). WCDA is 78000 $m^2$ in dimension and consists of 3120 water detector cells divided into 3 water ponds. A hemispherical 8-inch photomultiplier tube (PMT) CR365-02-1 from Beijing Hamamatsu Photon Techniques INC. (BHP) is installed at the bottom-center of each cell of the first water pond to collect Cher…
The Large High Altitude Air Shower Observatory (LHAASO) is planned to be built at Daocheng, Sichuan Province, China. The water Cherenkov detector array (WCDA), with an area of 78,000 m2 and capacity of 350,000 tons of purified water, is one of the major components of the LHAASO project. A 9-cell detector prototype array has been built at the Yangbajing site, Tibet, China to comprehensively understand the water Cherenkov technique and investigate the engineering issues of WCDA. In this paper, the rate and charge distribution of single-channel signals are evaluated using a full detail Monte Carl…
The Large High-Altitude Air Shower Observatory (LHAASO) is being built at Haizi Mountain, Sichuan province of China at an altitude of 4410 meters. One of its main goals is to survey the northern sky for very-high-energy gamma ray sources via its ground-based water Cherenkov detector array (WCDA). 900 8-inch photomultiplier tubes (PMTs) CR365-02-1 from Beijing Hamamatsu Photon Techniques INC. (BHP) are installed in the WCDA, collecting Cherenkov photons produced by air shower particles crossing water. The design of the PMT base with a high dynamic range for CR365-02-1, the PMT batch test system…
High precision and large dynamic range measurement are required in the readout systems for the Water Cherenkov Detector Array (WCDA) in Large High Altitude Air Shower Observatory (LHAASO). This paper presents a prototype of 12-bit 40 MSPS Analog-to-Digital Converter (ADC) Application Specific Integrated Circuit (ASIC) designed for the readout of 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 power-efficient Successive Approximatio…
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 major detectors for searching gamma ray sources. A Charge-to-Time Convertor (QTC) ASIC (Application Specification Integrated Circuit) fabricated in Global Foundry 0.35 μm CMOS technology, has been developed for readout of Photomultiplier Tubes (PMTs) in the WCDA. This paper focuses on the evaluation of this front-end readout ASIC performance. Test results indicate that the time resolution is better …
A water Cherenkov detector array, LHAASO-WCDA, is proposed 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 from 100 GeV to 30 TeV. In order to design the water Cherenkov array efficiently to economize the budget, a Monte Carlo simulation is proceeded. With the help of the simulation, cost performance of different configurations of the array is obtained and compared with each other, serving as a guide for the more detailed design of the experime…
The Large High Altitude Air Shower Observatory is in the R&D phase, in which the Water Cherenkov Detector Array is an important part. The signals of Photo-Multiplier Tubes would vary from single photo electron to 4000 photo electrons, and both high precision charge and time measurement is required. To simplify the signal processing chain, the charge-to-time conversion method is employed. A prototype of the front-end readout ASIC is designed and fabricated in Chartered 0.35 μm CMOS technology, which integrates time disctrimination and converts the input charge information to pulse widths. With …
The water Cherenkov detector array (WCDA) for the large high altitude air shower observatory(LHAASO) will employ more than 3600 hemisphere 8 inch photomultiplier tubes (PMT). The good time performance of PMT, especially the transit time spread (TTS), is required for WCDA. TTS is usually defined as the TTS of single photoelectron, and usually determined by using single photoelectron counting technique. A method using the photoelectron spectrum is researched for the measurement of TTS. The method is appropriate for multi-photoelectrons and makes it possible to measure the TTS of different photoe…
The KM2A(one kilometer square extensive air shower array) is the largest detector array in the LHAA- SO(Large High Altitude Air Shower Observatory) project. The KM2A consists of 5635 EDs(Electromagnetic particle Detectors) and 1221 MDs(Muon Detectors). The EDs are distributed and exposed in the wild. Two channels, Anode and Dynode, are employed for the PMT(photomultiplier tube) signal readout. The readout electronics proposed in this paper aims at the accurate charge and arrival time measurement of the PMT signals, which cover a large amplitude range from 20P.E(photoelectrons) to 2x10^5 P.E. B…
Large High Altitude Air Shower Observatory(LHAASO) is a composite cosmic ray observatory consisting of three detector arrays: kilometer square array (KM2A) which includes the electromagnetic detector array and muon detector array, water Cherenkov detector array (WCDA) and wide field of view Cherenkov telescope array (WFCTA). One of the main scientific objectives of LHAASO is to precisely measure the cosmic rays energy spectrum of individual components from 1014 eV to 1018 eV. The hybrid observation will be employed by LHAASO experiment, in which the lateral and longitudinal distributions of th…
The Large High Altitude Air Shower Observatory (LHAASO) is designed for high energy gamma ray and cosmic ray detection. A Water Cherenkov Detector Array which is sensitive to gamma ray showers above a few hundred GeV is proposed to survey gamma ray sources. The WCDA consists of 3600 PhotoMultiplier Tubes (PMT) which collect the Cherenkov light produced by the shower particles in water. Both high precision time and charge measurement are required over a large dynamic range from 1 photo electron (P.E.) to 4000 P.E. Prototype of an analogue front-end Application Specific Integrated Circuit (ASIC)…
