The Research On Distributed Electronics Of Water Cherenkov Detector Arrays Of LHAASO In Yangbajing Of Tibet

Cosmic ray physics links the cosmogony, the evolution of stars, the matter distribution in space and the high energy physics processes in the cosmic environment together by researching the high energy cosmic ray carried the message of macrocosmos and microcosm. In order to study the cosmic ray, there is a range of particle detection technology for observe EAS (Extensive Air Shower).LHAASO (Large High Altitude Air Shower Observatory) is going to be built in Yangbajing of Tibet in China at an altitude of 4300m a.s.l. It consists of a group of large detectors to study the energy spectrum measurement for the individual cosmic ray species above 30 TeV and below 300GeV. The water Cherenkov detector arrays, which are the sub detectors of LHAASO, are split into four sub arrays including 900 PMTs (PhotoMultiplier Tubes) with the size of 150×150 m2 each. With the aim of verificating the principle of physics, detector and electronics, a prototype detector including 9 PMTs would be set up first.The distributed electronics architecture, which is also called front digitization, is used to digitize the signals nearby in the front of the detector. In the large physics experiment with a large amount of channels and large scales in dimension, the physics message of the detector signals would be lost owing to the attenuations caused by the long cable from the detector to the lumped counting house. The advantage of the distributed electronics architechure is that there is no loss of the detector message because of the digitization defore-hand near the detector. My work have studied the distributed electronics architechure designed for the water Cherenkov detector arrays of LHAASO, including readout electronics, clock electronics and trigger electronics, especially on distributed scheme, high precious clock synthesis and distribution and PMT readout based on TOT (Time Over Threshold).Chapter 1 introduces the cosmic ray physics, the cosmic ray detection technology and the Cherenkov detector principle, and reviews the current state of the worldwide water Cherenkov detector experiments. Chapter 2 includes the design of the detector arrays in LHAASO, the analysis of detector in water Cherenkov detector arrays and the requirement of the readout and trigger electronics system.The distributed electronics architecture is studied in Chapter 3, including advantages and disadvantages of the distributed electronics architecture and the traditional lumped electronics architecture. That the lumped electronics architecture used in Daya Bay experiment and Super-Kamiokande experiment, and the distributed electronics architecture used in IceCube experiment and ANTARES experiment are discussed in this chapter. According to the characteristics of LHAASO, an electronics system baesd on distributed electronics architecture is designed for the water Cherenkov detector arrays, which consists of two parts. The Offshore part is used for readout PMTs near the detectors and the Onshore part is used to realize data transmission, clock distribution and trigger in the lumped counting room.The high precious clock synthesis and distribution which is the main technique of the distributed electronics architecture is researched in Chapter 4. It includes the high precious clock synthesis with the world common time and clock distribution based on synchronous clock distribution, asynchrounous clock calibration and PTP (Precision Time Protocol). The clock schemes of ANTARES experiment, IceCube experiment and White Rabbit Project are discussed. A scheme is designed including the clock synthesis baesd on GPS (Global Positioning System) and Ru frequency, and the clock distribution based on SERializer/DESerializer and fiber, as well as the transimission delay calibration based on echo principle.The detector readout is studied including traditional charge measurement, digital acquisition and TOT in Chapter 5. A lot of PMT readout electronics in the worldwide water Cherenkov detector experiments are discussed. A scheme based on TOT by QTC (Quantity-to-Time Converter) is designed for LHAASO.A prototype electronics system for verification the principle of the distributed electronics architecture is described in Chapter 6. The system consists of two modules: one is a VME (VersaModule Eurocard) 6U module as the prototype of Onshore electronics and the other is a USB (Universal Serial Bus) module as the prototype of Offshore electronics. This system is tested including the clock distribution, data transmission and online transmission delay calibration, and the results are positive.An integrate electronics system for the water Cherenkov prototype detector is developed in Chapter 7. This system includes a front end module and a back end module, and the front end module takes charge in readout the 9 PMTs for time and charge measurement based on QTC and TDC (Time-to-Digit Converter).