Design, production and test of intelligent PMTs for the JUNO experiment

Gao, Feng; Stahl, Achim (Thesis advisor); van Waasen, Stefan (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20kton liquid scintillatordetector currently under construction in a 700m deep underground laboratory in Guangdongprovince, China. Its main goal is to determine the neutrino mass hierarchy using electronantineutrinos from two nuclear power plants at a baseline of about 53km.The Online Scintillator Internal Radioactivity Investigation System (OSIRIS) is designedto monitor the radiopurity of the liquid scintillator while the JUNO detector is filled. Furthermore OSIRIS is used to confirm proper operation of the underground liquid scintillatorpurification plants. The main purpose of OSIRIS is to guarantee that the concentrations of238U and 232Th in the liquid scintillator do not exceed the acceptable rate limit.The OSIRIS detector consists of 18 tons of liquid scintillator contained in an acrylic vessel.This vessel is instrumented by 64 20inch PMTs, which are using the concept of an intelligentPMT. In this readout scheme, the electronics are mounted at the back of each PMT. Theacrylic vessel and the PMTs are immersed in a steel tank with ultra pure water. This waterpool is instrumented by 12 additional iPMTs and forms a Cherenkov veto. The pottingsystem is designed to encapsulate the electronics at the back of the PMT. Furthermore itprovides sufficient cooling for the electronics.In the potting system, a cylindrical PMMA piece is bonded to the PMT by a soft adhesive. The glue has to have enough strength to bond the PMMA and the PMT, and has to be elasticenough to protect the PMT from thermal stress when the ambient temperature changes. Astainless steel shell is glued to the PMMA piece to make a sealed system. The electronicssoldered on the PMT is immersed within oil in the shell. Heat, generated by the electronics,is transferred via oil and stainless steel to the cooled water. By this way, the electronics arekept at a stable temperature. For verifying the bond between the PMMA piece and the PMT, the bond between thePMMA and the shell, the tensile strength and the shear strength of the adhesives have beenconsidered and tested. For the whole potting system, the performance in pressurized waterand in an environment with changing temperature have been studied.For mass production, 80 iPMTs have been completed in Aachen. Totally 75 iPMTs passedthe iPMT verification after potting.

Institutions

• Department of Physics [130000]
• Chair of Experimental Physics III B [133510]