Measurement System Of Liquid Scintillator Temperature Field In JUNO Detector

The Jiangmen underground neutrino observatory experiment will be a large scale experiment for further study of neutrino after the Daya Bay neutrino experiment.In this experiment,the neutrino energy spectrum in the reactor will be accurately measured by a large neutrino detector,and the mass sequence of the neutrino will be determined.It is also possible to accurately measure the oscillation parameters of neutrinos and to study supernova neutrinos.The detector is a spherical vessel with an inner diameter of 34.6m and thick 12 cm,containing 20,000 tons of liquid scintillators,supported by stainless steel grid in a large pool of pure water.Two thousand 20-inch photomultiplier tubes(PMTs)were installed on the inner wall of the pool to detect cosmic rays,and 20,000 20-inch PMTs were installed on the grid to detect neutrino signals.Before performing the experiment,the PMTs need to be calibrated.During the calibration process,the calibration source used for calibration needs to be located,and the positioning scheme mainly based on ultrasonic positioning and visual positioning is supplemented.The ultrasonic location scheme uses ultrasonic ranging to achieve positioning function,and ultrasonic wave propagation speed in liquid scintillator medium is related to temperature.High precision positioning system needs to consider the influence of temperature,so the measurement of liquid scintillator temperature field in the detector is very important to the accurate measurement of the detector.The liquid scintillator temperature field measurement system is divided into two parts: the temperature measurement unit and the charge management unit.The temperature measurement unit is a front-end temperature acquisition device with miniaturization,low power,and lithium battery power supply,driven by the driving mechanism of the positioning system,the temperature data are collected and stored at the collection points of the liquid scintillator temperature field.After the temperature collection,the driving mechanism retracts the temperature measurement unit and connected with the charge management unit.The charge management unit charges the lithium battery,reads the temperature field temperature data of the temperature measuring unit and communicates with the computer processing unit of the positioning system.The temperature measurement unit is powered by 3.7V/100 mAh lithium battery.The low-power microcontroller communicates with the single-bus digital temperature sensor TSic506 to samples the temperature data,and communicates with the charge management unit through the self-defined single-bus communication interface.The charge management unit uses BQ25100 to control the charging of lithium battery,the microcontroller detects the charging voltage and current through the internal ADC module to judge the charging state,and reads the temperature field data of the temperature measurement unit through the single bus interface.The microcontroller also communicates with the computer processing unit of the positioning system through the RSM485 CHT isolation transceiver module.The function of the system is accomplished by circuit design,fabrication and programming.The temperature measurement unit was tested in South China National Centre of Metrology,and the temperature measurement error was less than 0.1?.The long-term experiment in the laboratory shows that the standby time of the temperature measurement unit is more than 24 hours,the storage temperature data is more than 500,the function of the charge management unit is complete,and all the indexes of the system meet the requirements.It can provide the function of temperature compensation for ultrasonic positioning system to meet the requirements of positioning accuracy.