At the end of 2011, at the age of 48, Liu Shulin made a significant decision to relocate his entire family from Xi'an to Beijing.
At that time, he served as the chief engineer of a subsidiary of a state-owned enterprise in Xi'an and was also one of the top experts in the field of microchannel plates. His career was on track, and life was comfortable.
What prompted Liu Shulin to make a major change was a sincere invitation from Wang Yifang, the director of the Institute of High Energy Physics at the Chinese Academy of Sciences. At that time, Wang Yifang's team was facing difficulties with their independently developed project on photomultiplier tubes and urgently needed Liu Shulin's assistance.
Previously, the market for photomultiplier tubes had been monopolized by Japan's Hamamatsu Corporation, and China lacked the ability to produce photomultiplier tubes with a diameter of more than 5 inches.
"Some advised Liu Shulin not to take this risk, saying there was only one design drawing, and it was questionable whether it could be realized. Even if it could, it would take a long time," said one person.
However, Liu Shulin remained resolute: "This matter is of great significance. I don't need to consider so much. I'll just go ahead and do it."
Wang Yifang, director of the Institute of High Energy Physics, Chinese Academy of Sciences, at the Photomultiplier Tube Laboratory.
Image provided by the Institute of High Energy Physics, Chinese Academy of Sciences
Decision to Independently Develop
"If we cannot produce large-size, high-performance photomultiplier tubes ourselves, everything will be subject to others' control."
Before Wang Yifang found Liu Shulin, he had led the team in the arduous effort of photomultiplier tube technology for three years.
The photomultiplier tube is a type of photon detector invented in the 1930s and widely used in medical equipment, scientific research equipment, nuclear technology, space science, and other fields.
Wang Yifang said, "It is like the 'eye' of the detector, capable of converting 'seen' photons into electrons, and then amplifying the electron signal by about 10 million times."
In 2008, while advancing the construction of the Daya Bay Neutrino Experiment, Wang Yifang's team also began planning for the future successor, the Jiangmen Neutrino Experiment. Unlike the Daya Bay Neutrino Experiment, which sought new neutrino oscillation modes, the main goal of the Jiangmen Neutrino Experiment was to measure the mass order of neutrinos.
Wang Yifang said, "To achieve this goal, we need to build a huge detector and increase the light collection efficiency to ten times that of the Daya Bay Neutrino Experiment, and five times the international top level. Therefore, the photon detection efficiency of the photomultiplier tubes used in the detector needs to be increased to 30%, which is twice the international level at that time."
Challenges followed.
At that time, only Hamamatsu Corporation in Japan could produce 20-inch photomultiplier tubes, but their performance did not meet the requirements, and their price was around 50,000 yuan each. The Jiangmen Neutrino Experiment planned to use 20,000 20-inch photomultiplier tubes, with a procurement cost of up to 1 billion yuan.
Wang Yifang thought it was too expensive!
What to do? We can only develop independently.
"If we cannot produce large-size, high-performance photomultiplier tubes ourselves, everything will be subject to others' control," said Qian Sen, a researcher at the Institute of High Energy Physics, Chinese Academy of Sciences, and one of the core members of the photomultiplier tube development project for the Jiangmen Neutrino Experiment.
In October 2008, Qian Sen, who was then pursuing a doctoral degree at the Institute of High Energy Physics, Chinese Academy of Sciences, was about to graduate. Wang Yifang suggested that he stay to participate in the development of photomultiplier tubes for the Jiangmen Neutrino Experiment.
Inspired by a project to develop large-area microchannel plate detectors, Wang Yifang outlined a conceptual design using microchannel plates to collect electrons, a different approach from the mainstream "dynode" type photomultiplier tubes.
Subsequently, Wang Yifang, Qian Sen, and others further refined the design, conducted analog verification, confirmed that the design was feasible. Six months later, they applied for a patent and successfully obtained invention patent authorizations from countries and regions including China, Russia, the United States, Japan, and the European Union.
Unexpectedly, they encountered difficulties in seeking cooperation with companies.
In the field of photomultiplier tubes, there were few domestic companies available for selection at that time. In the 1960s, China had two factories capable of producing photomultiplier tubes. Starting from the 1980s, Hamamatsu Corporation in Japan developed 20-inch photomultiplier tubes, leading the trend of photomultiplier tube technology and making it the world's best photomultiplier tube manufacturer. Later, Hamamatsu Corporation established a joint venture in Beijing, engaged in the production and sales of photomultiplier tubes, and the original domestic production enterprises gradually declined.
The team led by Wang Yifang searched for information, attended various conferences, and visited many research institutes and companies to seek cooperation. However, this innovative design was repeatedly rejected by companies for various reasons. Either "too busy with other tasks" or "never heard of it, seems unreliable."
Finally, after many searches and negotiations, Wang Yifang's team reached a cooperation intention with a research institute.
Initiating Joint Research
Researchers stationed at the factory, even moved laboratory equipment to the site
However, things did not go smoothly. After three years, this cooperation ended in failure.
"The photon detection efficiency of the sample tubes we produced only reached 5%, far from the requirement of 30%," Wang Yifang said.
After careful review and analysis, Wang Yifang's team believed that "it was not the design concept that was problematic; the basic principles had been validated, but rather the manufacturing process." After identifying the key problem, they began a new round of attempts.
Fortunately, a company that had previously failed to cooperate due to being too busy, North Night Vision Technology Co., Ltd. (now Northern Night Vision Technology (Nanjing) Research Institute Co., Ltd., hereinafter referred to as "Northern Night Vision"), expressed willingness to give it another try.
"This company has experience in producing microchannel plates. Although they have not made photomultiplier tubes before, they are willing and capable of doing so," Wang Yifang said, "I think this is very important. The key is whether you are determined to do something that no one else has done before."
At the same time, Wang Yifang followed expert advice and introduced Liu Shulin. Liu Shulin had a deep theoretical foundation and technical accumulation in the field of microchannel plates and was very familiar with the related industry, being a top expert in this field in China.
At the end of 2011, led by the Institute of High Energy Physics, Chinese Academy of Sciences, the Photomultiplier Tube Production-Industry-Research Cooperation Group was formally established, consisting of Northern Night Vision, Xi'an Institute of Optics and Precision Mechanics of the Chinese Academy of Sciences, China National Nuclear Corporation, and Nanjing University. The cooperation group established a new cooperation mode, formulated regulations, and discussed in advance how to determine the results and distribution ratio of benefits in the future, to avoid possible disputes, while encouraging everyone to make contributions and distribute based on contributions in the future.
The development of 20-inch photomultiplier tubes was full of challenges and uncertainties. Whether the new design can achieve the desired performance remains to be seen, only through efforts will it be known. In the following years, researchers from scientific institutes collaborated closely with technicians and workers from enterprises to overcome multiple technical challenges, including the preparation of high quantum efficiency photocathodes, fabrication and processing of microchannel plates and their components, and the development of large-sized glass shells with low radioactive potassium content.
According to Qian Sen's recollection, the team from the Institute of High Energy Physics of the Chinese Academy of Sciences mobilized all available resources. Researchers stationed themselves in factories, even relocating equipment from Beijing laboratories to production sites in Nanjing and Xi'an.
"While factory workers produced samples, researchers conducted on-site testing of intermediate processes. They then provided feedback based on data, indicating which steps had issues, which directions were worth improving, and which processes might be more effective," Qian Sen said. "This close collaboration enabled us to efficiently solve many challenges."
After four years of arduous efforts, the first 20-inch sample tube was finally successfully developed. During this period, the collaborative group held 39 meetings, conducted 8 joint research efforts, and completed over 150 reports on various development stages.
Wang Yifang remarked, "The final sample tube achieved a photon detection efficiency of 27%, only 3% shy of the 30% requirement."
Moving towards industrialization
The focus shifted towards achieving mass production and continuously developing new photomultiplier tube products for application in broader fields.
However, new challenges arose. Meeting the requirements for sample tubes was one thing, but the key was whether enterprises had the capability for mass production. Could they produce tens of thousands of 20-inch photomultiplier tubes on time and with consistent quality?
At the end of 2015, Northern Night Vision, upon receiving orders, immediately took action.
Sun Jianning, the general manager of Northern Night Vision, said, "The company began construction of the production line in 2016, and it was completed within a few months. The production equipment was independently developed by us and customized by manufacturers."
Their efforts paid off. On September 7, 2020, Northern Night Vision completed the order task on time and shipped all products to the testing site of the Jiangmen Neutrino Experiment in Guangdong.
Throughout the development, engineering, and mass production of photomultiplier tubes, all members of the collaborative group worked closely together, continuously optimizing processes and improving yield rates. This led to an increase in detection efficiency from an initial 27% to a steady 30%, and the yield rate increased from 50% to 80%, reaching an internationally leading level in electron vacuum devices.
"We obtained the best photomultiplier tubes and also received very favorable prices," Wang Yifang remarked.
Through participation in the development of photomultiplier tubes, Northern Night Vision explored new fields and growth points, accumulated technology and talent, and even revitalized the domestic photomultiplier tube industry.
In pursuit of sustainable development, the photomultiplier tube collaborative group continued to develop new photomultiplier tube products for application in broader fields such as nuclear technology, medical diagnostics, petroleum exploration, and environmental protection. This drive stimulated the development of upstream and downstream enterprises.
Today, Northern Night Vision has evolved from a company solely producing microchannel plates into a high-tech company with strong research and development capabilities.
"Collaborating with our researchers, the enterprise has also learned how to do things that have never been done before. There are fundamental differences in training between researchers and engineers, and the combination of the two is one of the most ideal models for technological development," Wang Yifang concluded.
