Research on the measurement of connecting bars’ axial force of JUNO central detector

Abstract

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy and precisely measure oscillation parameters and study the solar neutrino, supernova neutrino, geo-neutrino, etc. JUNO’s central detector (CD) has 20 kilo-ton liquid scintillator as target mass, which is contained by a huge acrylic sphere with the inner diameter of 35.4 m, and the acrylic sphere is supported by a stainless steel structure through 590 connecting bars. Part of the connecting bars bear pull force and the other bars bear push force. There is a direct relationship between the stress of connecting bars and that of acrylic sphere. For the installation process of the CD, the pretightening force and axial force of the connecting bars should be monitored with accuracy, and for the filling process and running condition, the precise measurement of axial force can indicate the safety of structure of the CD. Statistical method was used to evaluate the performance of measurement schemes, and 4-fiber Bragg grating measurement scheme was determined to be the final scheme, which can get the measurement uncertainty better than 0.7 kN. Performance of different measurement schemes are discussed in detail, and some related finite element analysis and evaluation method are also introduced in this paper.