Performance Study Of JUNO PMT And Measuremant Of Light Transmission Performance Of Protective Cover

The Jiangmen Underground Neutrino Observatory(JUNO)is a multi-purpose neutrino experiment.The main goal of which is determining neutrino mass hierarchy(MH)by detecting reactor antineutrinos from the nuclear power plant.A huge liquid scintillator(LS)detector with a 20 kton fiducial mass will be deployed in a laboratory 700 Meter underground,which was proposed to detect antineutrino and acheieve energy resolution of 3%/(?).In order to reach the requirement of this unprecedented resolution,about 18,000 20-inch photomultiplier tubes(PMTs)and 34,000 3-inch PMTs will be installed in the LS center detector required the PMT photocathode coverage more than 75%.The detector also requires PMTs with excellent properties:high quantum efficiency,and low noise performance,etal.In addition,approximately 2000 20-inch PMTs will be installed in the water pool to detect the Cherenkov light from cosmic-ray muons,acting as a veto detector.Case reconstruction also relies on the final performance of the detector.For the accuracy of case reconstruction in the central detector,the detector has specific requirements for charge resolution and time resolution of PMTs.The earth's magnetic field can affect the performance of the PMTs,because of the divergent trajectories of photoelectrons.JUNO is a high-precision experiment,so it plans to to reduce this effect with a compensation coil system.A performance test system included relative quantum efficiency(QE)and an anode signal measurement system for PMTs has been established in this paper.The relative QE test system was built by measuring the photocurrent of PMT.In laboratory,crate-type and desktop-type devices were employed for characterizeing PMT anode properties.At present,the crate-type system with QDC module mainly measures PMT charge spectrum,gain and charge resolution;And desktop device FADC test system mainly aquire PMT anode waveform signal through the waveform digitizer(Digitizer),so one can extract the relevant physical information of the waveform according to the experimental requirements.The results compared with the measurement of two test systems show that the relative deviation between QDC and FADC system is less than 10%.In this paper,we also acquired the PMT waveform signal by using the oscilloscope,and studied PMT time performance including transit time spread(TTS)and transit time(TT)with and without earth's magnetic field through waveform processing method.The results show TTS as a function of photoelectron numbers follows a behavior of a distribution a + b/(?).The shell of the PMT is made of fragile glass.If the glass shell is subjected to damage during the production,transport or installation,an implosion will happen when damaged glass shell is immersed in water.So PMT external need to add protective cover to prevent the occurrence and destruction of shock waves in water.The final chapter of this paper comprehensively measureed the light transmission performance of several transparent materials,and found that the transparency of acrylic material is better.