China Spallation Neutron Source Accelerator (Partial) Photo by Li Zifeng

In mid-August, Dongguan, Guangdong. The weather is sunny and rainy, and the air is humid and muggy. In the lush lychee forest, the China Spallation Neutron Source, the largest scientific project that has been built so far in my country with the largest single investment, is undergoing a summer shutdown for maintenance.
On August 23, 2018, the China Spallation Neutron Source Project passed the national acceptance and was officially put into operation. Since then, this former lychee forest has become popular.
The average annual number of public visits here exceeds 10,000. In one of the most popular offline popular science activities, scientific researchers received 6,000 people in half a day, and the cars that came to visit have been lined up from the gate of China Spallation Neutron Source to the highway intersection. Not only that, the competition for China's spallation neutron source machine is also fierce in the scientific and industrial circles, and the number of project applications has doubled year by year, so that only 29 out of every 100 applications are successful.
Why is this big device that has been running for 4 years so "hot"? Taking advantage of the shutdown for maintenance, the reporter of "China Science News" went deep into the field to find out.
Red, green, blue, yellow...
Good-looking: colorful "black technology"
Every year, the China Spallation Neutron Source has a "summer vacation" -- a downtime of one and a half to two months. During this time, researchers have to "maintenance" the device.
The China Spallation Neutron Source is a major national scientific and technological infrastructure supported by the National Development and Reform Commission. The legal entity is the Institute of High Energy Physics, Chinese Academy of Sciences. This device makes China the fourth country in the world to have a pulsed spallation neutron source after the United Kingdom, the United States and Japan.
Spallation neutron sources are often likened to "super microscopes" because they use accelerators to accelerate protons hit by neutrons on a target to probe the microscopic structure of matter. Its source, the accelerator system, is hidden underground like a Wolong.
17 meters underground, the air conditioning and fresh air system make the hot and humid air dry. Walking along the bright green aisle, people can see a colorful world of "black technology".
Yellow is a drift tube linear accelerator system that allows particles to "fly", blue is a quadrupole magnet that gathers particles into a beam, and red is a dipole magnet that allows particles to "bend" at a 15-degree angle ...
They were first strung in a long string, and then a large ring was formed. The long string section is a linear accelerator, and the ring section is a fast cycle synchrotron. Seemingly large and cumbersome equipment, the installation accuracy must reach the level of 10 microns to 100 microns, so that the tiny substances in nature, protons, can be controlled and accelerated as required.
Once running, every 1 second, the fast-cycle accelerator will "receive" 25 waves of negative hydrogen ions waiting to accelerate like a tourist bus. After each wave of negative hydrogen ions "gets on", it will be converted into protons and run about 20,000 laps along the fast-loop synchrotron in 0.02 seconds until the speed reaches 0.92 times the speed of light.
Then, the proton beam close to the speed of light rushes towards the heavy metal target like a "mini bullet", and the nuclei of the metal target are "shattered". Scientists also use special devices to slow down the uncharged neutrons in the "fragments" and introduce them into a spectrometer.
The spectrometer, located not far from the accelerator tunnel, is equally colorful.
The first phase of China Spallation Neutron Source has built three spectrometers, namely a general-purpose powder diffractometer with a green casing, a small-angle neutron scattering instrument, and a multi-functional reflector with a blue casing. In the past four years, China Spallation Neutron Source has also cooperated with universities and research institutions in the Guangdong-Hong Kong-Macao Greater Bay Area to build several spectrometers to meet the needs of national and local research institutions and enterprises.
Red, green, blue, yellow... With the target station as the center, the spectrometers that have been built and are under construction stretch out in all directions, making the China Spallation Neutron Source look like a blooming seven-color flower.
"The localization rate of our equipment has reached more than 90%." Chen Yanwei, director of the Spallation Neutron Source Science Center and deputy director of the Institute of High Energy Physics of the Chinese Academy of Sciences, told the "China Science News" that nearly 100 cooperative units nationwide have completed the installation of various equipment. The development and mass production of equipment, many of which have reached the international leading or advanced level.
5000, 97%, 800, 122%...
Easy to use: The "superpower" of a super microscope
In China's spallation neutron source, researchers like to talk with numbers.
The number they are most proud of is "5000". Here, time is not calculated by year, month, or day, but by hours. "We shoot 5,000 hours of neutron beams every year," said Chen Yanwei.
5,000 hours means that for more than 8,700 hours a year, the China Spallation Neutron Source is producing neutrons most of the time and conducting experiments. "Among other spallation neutron sources in the world, the neutron beam time in the UK and Japan is generally around 4,000 hours per year." Chen Yanwei said.
Another number they are proud of is "97%". "From 2020 to 2021, our actual operating efficiency will exceed 97%, which is an efficiency that no other spallation neutron source in the world can achieve." Deputy Director of the Spallation Neutron Source Science Center and a researcher at the Institute of High Energy Physics, Chinese Academy of Sciences Wang Sheng said that the actual operating efficiency is the ratio of the actual operating time of the spallation neutron source to the planned operating time. The higher the number, the lower the failure rate of the spallation neutron source and the better the stability of its operation as planned.
When describing the operational effectiveness of China's spallation neutron source, they like to use the number of topics to illustrate. "In the past 4 years, China's spallation neutron source has been opened for 8 rounds, and more than 800 projects have been completed, focusing on supporting the timing of major national demand projects." Chen Yanwei said.
Facing the frontiers of world science and technology, they have carried out research on super steel, molecular sieve adsorbents, and quantum materials.
Facing the main economic battlefield, they have provided important support for high-tech enterprises and research institutions such as the General Iron and Steel Research Institute, Guodian Power Development Co., Ltd., and China National Petroleum Corporation in the fields of high-performance chips, batteries, materials, and stress testing. .
Facing the country's major needs, they completed the stress test of aerospace engine blades and verified the welding process of the "Striver".
Facing people's life and health, they successfully developed my country's first boron neutron capture therapy experimental device with completely independent intellectual property rights in August 2020, and began to install it in Dongguan People's Hospital at the end of July this year.
Good data and results snowball users. According to Chen Yanwei, at present, there are more than 3,800 registered users, the number of projects applied for from 2021 to 2022 has increased by 122% year-on-year, and the pass rate of project applications is 29%.
Improve power, optimize performance, add terminals, do crossover...
Good Conspiracy: "Small Goals" for the Future
The increasing number of timing applications and the intensifying technological war have made the "upgrade" of China's spallation neutron source a reality.
As early as the beginning of engineering design, researchers have reserved space for device upgrades. Because of this, the future can be upgraded directly on the basis of the first phase of the project.
According to Chen Yanwei, at present, China's spallation neutron source has completed all the design indicators of the first phase. In February 2020, the target beam power reached the design target of 100 kW, a year and a half earlier than the original plan; in February 2022, the target beam power reached 125 kW, exceeding the design target by 25%, and achieved stable and efficient operation. Significantly improved device performance.
Increasing the target beam power will make the device generate more neutrons in the same time, thereby shortening the experiment time and improving the sample resolution. "It's like taking pictures during the day when the light is strong, the exposure time will be shorter than when taking pictures at night, and the pictures will be clearer." Chen Yanwei explained.
One of the "small goals" of researchers in the future is to increase the target beam power to 500 kilowatts to make the neutron source "brighter".
In addition, Liang Tianjiao, deputy director of the Spallation Neutron Source Science Center, introduced that after the upgrading and reconstruction of China's Spallation Neutron Source, it is expected to cover most fields of user needs, meet more scale structure and dynamic characterization, and provide multidisciplinary research. Provide stronger support.
Now, taking advantage of the summer shutdown for maintenance, the researchers here are making preliminary preparations for the new spectrometer and experimental terminal to be installed. For the future progress of the device, "Science China Journal" will continue to pay attention.
(Original title "Into China's Spallation Neutron Source - Fourth Anniversary of Operation, "Three Good Students" in the Large Installation")