Research On CCD Positioning Subsystem In JUNO Calibration System

Jiangmen Underground Neutrino Observatory(JUNO)is a larger neutrino detection experiment after the Daya Bay neutrino experiment.By detecting the energy spectrum of neutrino to accurately measure the neutrino mass order and neutrino oscillation parameters.It has a profound influence in studying the composition of particle and the origin of the universe.The core part of JUNO is the central detector(JUNO-CD),neutrinos react with the liquid scintillation(placed in an acrylic sphere with an inner diameter of 35.4m)to emit photons in JUNO-CD,photons are converted into electrical signal by 25000 20-inch photomultiplier tubes(PMTs)on the stainless steel shell of the central detector.Electronic devices obtain the neutrino energy spectrum by analyzing the signal and research it.The PMTs need to be calibrated and the method is to make the calibration source traverse the specified coordinates in the detector,so the calibration source needs to be positioned.The thesis only discusses the CCD visual positioning.The main work and findings of this thesis are as follows:1)It proposes the detection scheme of "active light source + CCD camera".The active light source with the calibration source moves in the acrylic sphere of the detector,the CCD cameras placed in the stainless steel shell position it.And the CCD detection target is determined that the positioning error of CCD vision positioning system in the acrylic sphere is less than 3 cm.2)It designs the active light source circuit.The light source circuit is composed of the power supply and control unit and the wireless light source unit.The PLC host uses RS485 to communicate with the power supply and control unit.The Power supply and control unit transmits host commands by using Ir DA technology.It charges the 3.7V/100 m Ah polymer lithium battery in the wireless light source sealed shell by transmitting energy through the coil.The wireless light source can work for more than 24 hours after being fully charged that meet the CCD visual positioning requirements.3)It analyzes the light path from the light source to the CCD camera in the multi-media environment.Light from active light source passes through the liquid scintillation,acrylic ball,water and then enters the CCD camera.It is the refraction that changes the light path of the light source.It verifies the relationship of the viewing angle of the CCD in the liquid scintillation and the viewing angle of the CCD in the air by theoretical analysis.Finally,the suitable CCD camera and lens were selected by considering the observation field of view,low distortion and other factors,which were proved to meet the experimental requirements by experimental analysis and verification.4)It researches the image distortion in multi-media environment.According to the causes of nonlinear phenomena,it uses the piecewise linear interpolation and the polynomial interpolation to solve the problem in the thesis.Both of them could meet the experimental requirements and the polynomial interpolation is better.And then conducts preliminary research on the positioning algorithm experiment by experiment,the positioning accuracy is better than 3cm which meets system design requirements.