【Ten Years of Great Development in Chemical Equipment】1973–2024 – Like it! World’s largest glass sphere buried 700 meters underground has been built! !
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Safety first. Prevention first: Let’s praise and encourage the achievements in China’s chemical engineering technology and equipment. **********************【Ten Years of Rapid Development in Chemical Engineering Equipment】A continuously updated summary post is available; feel free to join the discussions at https://bbs.hcbbs.com/thread-3576046-1-1.html (Source: Haichuan Chemical Engineering Forum) ***************** Reporters learned today (October 11, 2023) from the Chinese Academy of Sciences that the world’s largest single acrylic sphere, located inside the central detector of the Jiangmen Neutrino Experiment (JUNO), which is buried 700 meters underground, has been fully constructed, and the project is now in its final stages. Neutrinos are the oldest and most primitive fundamental particles that have existed since the beginning of the universe; they carry a great deal of important and mysterious information. Studying neutrinos is of vital significance for understanding the universe and the matter that constitutes our world, and it represents one of the cutting-edge fields in basic science on an international level. The Jiangmen Neutrino Experiment has as its primary scientific goal the measurement of the order of neutrino masses, while it also conducts a number of other important cutting-edge research projects. Its core detection apparatus is located at a depth of 44 meters in a pool situated within an experimental hall buried 700 meters underground. It consists of a stainless steel mesh shell with a diameter of 41 meters, a plexiglass sphere with a diameter of 35.4 meters, as well as key components such as 20,000 tons of liquid scintillator and 45,000 photomultiplier tubes.
The Jiangmen Neutrino Experiment was approved in 2013; construction of the underground experiment chamber began in 2015. By the end of 2021, the underground chamber was ready for use and detector installation commenced. At present, the plexiglass spheres on the innermost layer of the detector at the Jiangmen Neutrino Experiment Center have been assembled, and the outer stainless steel framework as well as the photomultiplier tubes are also being installed in an orderly manner. It is expected that all installation work will be completed by the end of November, after which the filling of ultra-pure water and liquid scintillators will begin. The facility is scheduled to start operating for data collection in August 2025, with an expected operational life of around 30 years. The Jiangmen Neutrino Experiment’s plexiglass sphere has an inner diameter of 35.4 meters; it is constructed by bonding 263 plexiglass panels that are 12 centimeters thick, along with upper and lower chimney structures. The total weight of the plexiglass material is approximately 600 tons, making it the largest single plexiglass sphere in the world. In fact, compared to its 35.4-meter diameter, a 12-centimeter-thick plexiglass sphere is, on a proportional basis, as thin as an eggshell. Acrylic sheets are produced using unique formulas and processes, offering high light transmittance and a low background level; the mass fraction of naturally occurring radioactive elements uranium and thorium is less than one trillionth. The bonding of acrylic balls employs bulk polymerization technology involving large-scale material injection, polymerization, and annealing; the total length of the bonding seams is approximately 2 kilometers, and special methods are used to protect these seams.
The plexiglass sphere, serving as the container for the liquid scintillator that is used as a target for detecting neutrinos, will hold 20,000 tons of liquid scintillator. The entire sphere operates in pure water, and it must withstand a buoyant force of around 3,000 tons over an extended period of time. This force is transmitted to the main stainless steel mesh structure through plexiglass joints, connecting rods, and stainless steel joints; sensors are installed on these connecting rods to monitor the forces acting on them. A specially designed stainless steel structure is embedded in acrylic to serve as an acrylic joint; through repeated design optimizations and hundreds of tests, an extremely high load-bearing capacity was achieved. Additionally, some of the stainless steel joints utilize a disc spring design, which effectively improves the stress distribution within the acrylic joints.
To build this large-scale scientific facility, the Jiangmen Neutrino Experiment team pooled their expertise and took various measures to overcome numerous technical challenges: 1. They successfully developed photomultiplier tubes with the highest photon detection efficiency in the world, owning independent intellectual property rights; this breakthrough ended the international monopoly in this field, and patents were granted by the EU, the United States, Japan, and other countries. 2. Developed an underwater explosion-proof system using photomultiplier tubes with high strength, high precision, and high light transmittance. 3. A high-purity, highly sealed, and highly efficient liquid scintillator purification system was developed, resulting in the liquid scintillator with the highest attenuation length available internationally to date. 4. An innovative design using underwater electronics enables aerospace-grade reliability through civilian components. 5. Complete the design, development, mass production, and installation of key components of the detectors, such as acrylic balls and stainless steel mesh structures. 6. The country’s largest deep-buried underground chamber was constructed, with a vaulting span at its ceiling reaching 49.5 meters; the construction involved world-class, unconventional underground engineering.