Study On Performance Of Large Dynamic Range Photomultiplier Tube For LHAASO

Since the discovery of cosmic ray by Hess in 1912,its origin and composition have been an important subject in physics.Through a lot of research and exploration,the main component of the cosmic ray particles is well understood,while for the origin of these particles,the acceleration and transmission mechanism,there are still no exact answers.Thus,searching for the source of the original high energy cosmic rays by measuring its composition,energy spectrum and incident direction is the key problem in the study of cosmic ray physics.Aiming at this problem,the Large High Altitude Air Shower Observatory(LHAASO)project is scheduled to be built at Haizi mountain in Sichuan province at elevation of 4410 m.As a large scale complex of various detectors,its primary scientific goals in-clude exploring the origin of cosmic ray,searching for very high energy gamma ray sources,and study new physicals like Lorentz invariance,dark matter and quantum gravity.The proposed project consists of three detector arrays:1 km2 extensive air shower array(KM2A),78000 m2 Water Cherenkov Detector Array(WCDA)and 12 Wide Field of view Cherenkov Telescope Array(WFCTA),using several different ob-servation methods to achieve accurate measurement of the cosmic ray.WCDA,which uses the water Cherenkov detection technology,is located in the middle of the LHAASO detector and proposed to target gamma astronomy between 100 GeV and 30 TeV.It is divided into 3000 units of detector,with each cell size of 5 m×5 m under 4.4 m-depth.A 8-9 inches photomultiplier tube(PMT)is installed at the bottom-center of each cell to collect the Cherenkov light produced by shower particles crossing water.As the readout of detector unit,the performance of each PMT directly affects the performance of WCDA.According to the scientific goals and Monte Carlo simulation,each PMT requires not only good single photoelectron(SPE)resolution(Peak-to-Valley ratio>2.0),fast time response(TTS<4.0 ns)and low darknoise rate(<5 kHz@/4 PE),but also large dynamic range up to 4000 PE.Among them,the large dynamic range of 1-4000 PE is far greater than the dynamic range of each candidate PMT using the readout circuit provided by the manufacturer,and is also much larger than that of the similar experiments in the world.The key problem to be solved for WCDA is to extend the dynamic range of PMT under the premise of ensuring the single photoelectron resolution and time performance.The main work of this thesis is to design the large dynamic range readout circuit for each of the three candidate PMT XP1805,CR365 and R5912 according to the re-quirements of WCDA,detailedly study the measuring method,including the gain,high voltage response,transit time spread,dark noise rate,afterpulse rate and non-linearity,and finally determine the readout circuit design through amounts of experiments.The measurement results show that under the voltage divider and readout circuit specially designed,each candidate PMT is well qualified for LHAASO-WCDA,and the key prob-lem for WCDA development is solved.In addition,the measurement results can provide data reference for the finally determination of WCDA-PMT.LHAASO-WCDA requires a total of 3200 PMTs and all these PMTs need to be measured in detail before installed.According to the test requirements for a large num-ber of PMTs,another major work of this thesis is to build a batch test system and pro-pose a complete PMT performance batch test scheme.The key problems in the batch test system is solved,including the light source,signal process,switch between differ-ent measurement items,control and so on.Except for just one manual operation from the SPE measurement to non-linearity measurement,all the other measurement process can be realized by software control.A small batch test using the candidate PMT sample tubes is performed.The results further verify the feasibility of the batch test system and the test scheme,and the measurement precisions can also meet the requirement of WCDA experiment.KM2A,acts as the main array of LHAASO,consists of electromagnetic particle detector(ED)and the underground Muon Detector(MD),it is used to detect the elec-tromagnetic particles and muons in the air shower.MD also uses the water Cherenkov detection technology and is divided into 1171 detection units.Each unit is a water bag,and a 8-9 inches hemispherical PMT is installed at the top of the water bag to receive the Cherenkov light.According to the Monte Carlo simulation,the MD unit must achieve at least a dynamic range from 1 to 10000 muons,which requiring the PMT output cur-rent above 1.6 A.That is the main problem to be solved for MD-PMT.According to the special requirememts of MD,I designed the large dynamic range readout circuit for the candidate PMT R5912 and XP1805.The feasible design scheme is determined though amounts of experiment,and the measurement results show that both the candi-date PMTs can meet the demands of MD.According to the test requirements of more than 1200 PMTs in MD experiment,the similarities and differences between batch test of MD-PMTs and WCDA-PMTs,the PMT batch test system for WCDA is extended to MD,and a complete batch test scheme is proposed.During the thesis research period,the cosmic ray physics and the related core prob-lems and experimental methods are investigated.According the LHAASO project and the two detector arrays WCDA and MD,the performance of large dynamic range PMT is detailedly researched.The dynamic range readout design scheme of each candidate PMTs is proposed and the key problems of WCDA and MD readout design is solved.The measurement method of PMT performance is studied and optimized,which lays the foundation for PMT batch test.All these researches are of great significance for the construction of LHAASO project.