PMT Array Research For The Wide Field Of View Cherenkov/Fluorescenee Telescope Array Of The LHAASO

Cosmic rays are energetic charged particles coming from extraterrestrial sources, and their origins are not clear yet although they were discovered about one hundred years ago. One of the major scientific goals of the Large High Altitude Air Shower Observatory (L-HAASO) is to explore origins of cosmic rays by means of a hybrid ground-based detector array which will cover an area of 1 km2. The Wide Field of view Cherenkov/fluores-cence Telescope Array (WFCTA) is one of the main detectors of the LHAASO. By using a spherical mirror, the Cherenkov lights or fluorescences of extensive air showers induced by primary cosmic rays are focused on the photomultiplier tube (PMT) array (camera) lo-cated at the focal plane of the WFCTA, the information on the lateral photon density dis-tribution and longitudinal shower development can be recorded by the telescope camera. The species and the energy of the primary cosmic ray can then be reconstructed with these shower development informations. Thus the telescope performance is closely related to the performances of the PMTs in camera. The main content of this thesis is to study the PMT array of the WFCTA.To test the performance parameters of candidate PMTs and 12500 PMTs which will be used in the WFCTA, two dedicated PMT characteristics test systems are designed and fabricated. The single photo-electron spectrum, voltage vs. gain characteristics and pulse linearity are measured by using a system which is named 1D-system. The anode output spatial uniformity is measured by using another system which is named 2D-system. In the 1D-system, the incident light flux of PMT cathode is controlled by adjusting the distance between the light source and the PMT. and by shifting the exit aperture of the light source. The light flux can be adjusted in a range of 3.9 orders of magnitude by this means, and 16 pieces of PMTs can be tested in a single run in 1D-system. In the 2D-system, a LED coupled optic fiber is served as a light source, and the optic fiber casts an approximately 1 mm diameter light spot on the PMT cathode. The light spot is driven by a X-Y translation stage to automatically scan the PMT cathode in a 1 mm steps. The ROOT framework is embedded in the test system control software, test results can be automatically displayed in a coordinate graph after the system have completed the test. The real-time test results of the anode output spatial uniformity can be displayed in the 2D-system control software. The memory mapping and multi-thread techniques are adopted, and the test data processing rate is significantly improved.The characteristics of the candidate PMTs:Hamamatsu R1924A,CR303,CR332A, R7899 and CR364, and HZC Photonics XP3102 and XP3182 are evaluated by using the systems mentioned above. In light of the test results, all of the candidate PMTs achieve a 2 x 105 gain with an operation voltage of lower than 1400 V. The flat cathode CR303 exhibits poorer anode output spatial uniformity (13.4%) compared with the other tubes. The anode output spatial uniformities of the other tubes, which have a spherical cathode, are 6.5%?10.6%. However, only the CR364 (R7899) and XP3182 meet the pulse dynamic range requirement of the WFCTA. The anode peak current values at which the linearity is degraded by 2% exceed 100 mA. In the case of the XP3182 the corresponding anode current exceeds 90 mA. By contrast this linearity degradation is 30-40 mA for the other tubes. An improved fitting method is presented to precisely fit the single photo-electron spectrum according to our test condition.The structure of this thesis is as follow:Chapter 1 is an introduction. The develop-ment of cosmic rays detection technology, especially the ground-based, and the general mechanism of extensive air shower are reviewed in chapter 2. In chapter 3, the major scientific goals and the detectors design are introduced briefly, the physical goals and performance requirements of the WFCTA are described. In chapter 4, the PMT specifica-tions which related to the WFCTA performances are analyzed, and 7 models of candidate PMTs are then chosen out according to the performance requirements and the physical features of observation objects of the WFCTA. The hardware and software design and performance verification results of the PMT systems are described in detail in chapter 5. The test methods, procedures and results of the candidate PMTs selection are reported minutely in chapter 6. As a pre-research, the PMT array assembly techniques are also proposed in chapter 7. The chapter 8 is a summary and outlook of our work.