Chen Hesheng | China Spallation Neutron Source

About half of the Nobel Prizes in Physics and Chemistry are related to large scientific facilities.

Or the new ideas proposed have been verified on large scientific facilities,

Or large scientific facilities provide the most advanced research methods,

A major scientific breakthrough has been discovered or a new technological invention has been made.

Chen Hesheng, Academician of the Chinese Academy of Sciences, Chief Commander of the Spallation Neutron Source Project

Scientific Discussions in the Bay Area | May 19, 2019 Guangzhou

▲ China Spallation Neutron Source

This is the China Spallation Neutron Source in Dalang, Dongguan, Guangdong, covering an area of ​​about 400 acres. It is a typical large scientific facility. In front of it is the branch line of the Pearl River Delta Ring Expressway G94 - 9411, connecting Humen to Huizhou.

Why did we build a spallation neutron source? Why did we choose Dongguan, Guangdong? What are the results of our construction? What are the preliminary experimental results?

▲ The 20th century: the century of physics

Physics in the 20th century experienced three major leaps, from atomic physics to nuclear physics and then to particle physics. More than a hundred years ago, we discovered that atoms are composed of nuclei and electrons, and later we discovered that nuclei are composed of protons and neutrons. Since the 1960s, we have gradually discovered that the protons and neutrons that make up the nucleus are composed of quarks.

It should be said that the three leaps forward in physics in the 20th century have yielded tremendous research results and transformed into tremendous productivity. For example, nuclear power, semiconductors, lasers, computers, GPS, etc., which are now widely used, are all inseparable from the progress of physics in the past century.

At the same time, these technologies have had a profound impact on society and politics. On the one hand, nuclear weapons have always been a very serious international political issue. On the other hand, the Internet that we use widely today was also invented during the study of the structure of matter in physics in the last century.

The three leaps forward in physics not only provided services for the development of physics, but also produced advanced research methods, including large scientific facilities such as synchrotron radiation sources and spallation neutron sources.

A symbol of national comprehensive strength

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As the study of the structure of matter deepens to the level of atomic nuclei and particles, we need particles with higher and higher energies to study smaller and smaller scales, which requires the use of large scientific facilities.

The construction of China's large scientific facilities originated from the Beijing Electron-Positron Collider. This was a major decision made by Comrade Deng Xiaoping in the mid-1980s. He said: We are building the Electron-Positron Collider to make China's high-tech occupy a place in the world. It should be said that Comrade Xiaoping's strategic goal is gradually being realized.

There are two types of large scientific facilities. One is accelerators dedicated to particle physics and nuclear physics, nuclear fusion devices, and large astronomical telescopes such as the "Sky Eye" in Guizhou; the other type is synchrotron radiation facilities, spallation neutron sources, free electron lasers, etc.

Large scientific facilities are called "major scientific infrastructure" and "large scientific projects". They have become one of the key units of the national science and technology innovation system and a symbol of the country's comprehensive strength.

Over the past few decades, research based on large scientific facilities has achieved major scientific breakthroughs. The construction, operation and research of large facilities have produced many major scientific and technological innovations, and have strongly promoted the development of high-tech.

According to statistics, about half of the Nobel Prizes in Physics and Chemistry are related to large scientific facilities. Either the new ideas proposed were verified on large scientific facilities, or large scientific facilities provided the most advanced research methods, discovered major scientific breakthroughs, or obtained new technological inventions.

Why build a spallation neutron source?

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▲ 1994 Nobel Prize in Physics

Neutron scattering is a super microscope for detecting matter. Brockhaus of Canada and Schall of the United States first proposed this innovative idea. Brockhaus proposed that neutron scattering can detect the position of atoms, molecules and their clusters, while Schall believed that it can not only detect the position but also its movement. So they won the Nobel Prize in Physics in 1994.

Why do we use neutron scattering to study the structure of matter? Currently, the main means of studying the structure of materials are synchrotron radiation sources and spallation neutron sources.

Synchrotron radiation is used to detect the distribution of electrons outside the nucleus, while neutron scattering can measure the direction and energy distribution of neutrons after scattering with the nucleus of the sample. It can detect the magnetism of matter, the position of atomic nuclei, and large engineering samples. Because of its good penetrating power, it can also detect dynamic processes in matter.

Compared with synchrotron radiation sources, spallation neutron sources are expensive, technically complex, difficult to detect, and difficult to experiment with. Therefore, there are only four spallation neutron sources in the world, while there are about 60 synchrotron radiation sources. However, many key issues in cutting-edge science and bottleneck issues in the sustainable development of the national economy and national security can only be solved with spallation neutron sources!

Where do neutrons come from? One way is from reactors. There are reactors in Mianyang, Sichuan and the Institute of Atomic Energy in Beijing. They are produced through chain reactions. There are about 30 reactors in the world.

Another method is the spallation neutron source. It uses particles to hit heavy metal targets. It does not use nuclear fuel and is not a nuclear device, so it has very low safety requirements. It is difficult to find a place to build a reactor in the world now, so neutron research is slowly moving towards the spallation neutron source, which has many advantages.

How does a spallation neutron source work? We use high-energy protons to hit a target, and the resulting neutrons hit the sample, which we then detect.

What are the functions of neutrons? First, it has magnetic moment, so it can be used to study magnetic structures. Computer storage is made of magnetic materials, and superconductivity is also closely related to magnetism, so it is a very key technology for studying magnetic materials.

The second is that it can distinguish light elements and isotopes. As you can see, the cross section of the reaction between neutrons and various atomic nuclei varies greatly, unlike synchrotron radiation, which is proportional to the square of the charge of its nucleus, so it is not sensitive to light elements.

For example, when using synchrotron radiation to analyze the protein molecules of lysozyme, you cannot see the carbon, oxygen, and nitrogen, but when using a spallation neutron source, you can see the hydrogen atoms, and the content is much richer. Similar high-temperature superconductors and other various structures require a spallation neutron source.

For another example, everyone is very concerned about methane hydrate, which is a kind of energy that can provide us with clean and sustainable development. However, we need to understand the properties of methane hydrate. If we mine it without understanding its properties, it may cause some natural disasters.

Therefore, we must simulate the high-pressure environment of methane hydrate and conduct in-depth research on it. Simulating a high-pressure environment requires a very thick container that can only be penetrated by neutrons. In addition, the effect of using neutron scattering to study carbon and hydrogen elements is also relatively good, which makes the spallation neutron source a necessary and indispensable means for studying the internal microstructure of methane hydrate.

Academician Mao Heguang conducted research on methane hydrate at the Los Alamos National Laboratory in the United States more than ten years ago, which is very important for our applications.

The third and most important thing is that it can directly study the residual stress of large engineering specimens in situ. What does in situ mean? General experimental devices are used to study very small samples, but this cannot solve all problems. Many problems require the study of large engineering specimens.

For example, 20 years ago, a serious accident occurred on a German high-speed train, killing more than 100 people. It was finally discovered that the cause of the accident was metal fatigue in its wheels. How can we find the law of metal fatigue? The solution is to measure the properties of the wheels under different operating conditions: when they were just built, after running 18,400 kilometers, and after running 60,000 kilometers, we studied their metal fatigue conditions and obtained scientific operation and maintenance laws.

▲ UK Spallation Neutron Source: In-situ measurement of temperature and stress distribution during A380 wing welding and riveting to optimize the process

Another very interesting example is the UK Spallation Neutron Source. The welding and riveting of the Airbus A380 wing. The welding and riveting process is very complicated. For example, if the riveting is too light, it will not be riveted, and if the riveting is too heavy, the riveted part may be easily broken in the future. The same is true for welding. Airbus put a section of the A380 wing into the UK Spallation Neutron Source, riveted and welded it at the same time, and measured the changes in its temperature and stress at the same time, and thus came up with the best process.

There is also the Spallation Neutron Source in Japan, which has done very interesting things. The key to electric vehicles lies in the battery. How can we make the battery larger, faster to charge, and safer? On the one hand, we need to find better materials, and more importantly, we need to study how to make batteries, and look at the relationship between the macroscopic performance changes of the battery and the microscopic performance changes of the internal materials.

The whole battery can be placed in a spallation neutron source and charged and discharged hundreds of times to see how the performance changes, the transport of particles inside, and the properties of the electrodes. Japan has used this method to achieve a battery capacity of 400 kilowatt-hours per kilogram.

In addition, everyone is very concerned about the safety of batteries, such as the appearance of flammable gas and explosion during the charging and discharging process. This gas can only be detected by neutrons, and we can use the spallation neutron source to study under what circumstances the gas will appear.

Achieving innovation by overcoming challenges

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This is the China Spallation Neutron Source, which consists of a linear accelerator 80MeV (MeV, energy unit, mega electron volt), a fast-cycling synchrotron accelerator 1.6GeV, a target station, and three neutron scattering spectrometers. It was jointly built by the Chinese Academy of Sciences and the Guangdong Provincial Government. The legal entity is the Institute of High Energy Physics of the Chinese Academy of Sciences. A total investment of 1.86 billion was made and it was completed in March 2018.

▲ Spallation reaction and neutron scattering principle

The generated neutrons hit the sample and then shoot onto the component, and we detect them. This is the principle of spallation and neutron scattering.

It takes a long time for a large scientific facility to be built from the idea of ​​​​proposing it. In the late 1990s, we were already conceiving of the idea of ​​a spallation neutron source. In 2000, we submitted a report on the "Development Goals of China's High Energy Physics and Advanced Accelerators" to the National Science and Education Leading Group, proposing the construction of a spallation neutron source. It took 18 years until last year to complete it.

Why is the Spallation Neutron Source located in Dongguan?

In 2000, Lu Yongxiang, then President of the Chinese Academy of Sciences, put forward an idea. He hoped to combine the Chinese Academy of Sciences' strong strength in basic research and applied basic research with Guangdong Province's strong economic strength and urgent need for scientific and technological innovation and industrial demand upgrading, and build the Chinese Academy of Sciences' "third high ground" in the Pearl River Delta.

The idea of ​​a spallation neutron source was conceived in 2000 and was approved by the National Science and Education Leading Group in 2004. However, there was no place to build it in Beijing. In February 2006, I attended a meeting organized by the Provincial Development and Reform Commission in Guangzhou and talked with the leaders of the Development and Reform Commission about finding a construction site for the spallation neutron source.

Secretary Zhang Dejiang and President Lu Yongxiang made the decision to locate the Spallation Neutron Source in Guangdong. This is a far-sighted strategic deployment, and now it has become the core large scientific facility supporting the Guangdong-Hong Kong-Macao Greater Bay Area Science and Technology Innovation Center.

In May 2006, the Provincial Development and Reform Commission organized an inspection tour of Zhuhai, Luogang and Songshan Lake. Songshan Lake was the most suitable, and Dongguan provided the strongest support. It was rare to have such a foresight 13 years ago.

The United States spent $1.4 billion on the spallation neutron source, Japan spent $1.8 billion on the spallation neutron source, and China spent RMB 1.8 billion on the spallation neutron source. This spallation neutron source has a series of innovative ideas, and its main performance exceeds that of the British spallation neutron source, and the localization rate of the equipment exceeds 90%.

During the construction process, we overcame many difficulties. One of the biggest difficulties was that the linear accelerator tunnel we built was located 19 meters underground. It leaked water in the first rainy season after its completion. It was not because the construction unit cut corners, but because they mistakenly referred to the construction experience of the Shanghai Light Source.

An expert from Shanghai Light Source said: The concrete wall of the tunnel is one meter thick, so less cement is needed. Shanghai Light Source used 150 kilograms of cement per cubic meter of concrete, while we used 180 kilograms. But the situation is different. We are 19 meters underground. The groundwater in the south is very abundant, so there was a serious water seepage problem in the first rainy season.

Finally, we had to add another layer of tunnel outside the linear tunnel to waterproof it, which delayed the project by a year and a half. In order to catch up with the time and ensure the project was completed on time, we adopted a parallel work approach, first installing and debugging the equipment that needed to be installed underground on the ground, and then dismantling and putting them underground after the tunnel was repaired. This workload was very large.

This is the target station spectrometer hall, the linear accelerator equipment building and the fast-cycling synchrotron accelerator.

This is the 200-meter-long straight tunnel and the 240-meter-long ring tunnel of the circular accelerator.

This is the core installation device of the target station. As you can see, it is installed step by step.

▲ 25Hz AC magnet

We have made many innovations and overcome many challenges. For example, the current of the magnet reaches 1,000 amperes and 25 Hz. Older comrades remember that the ballast of the fluorescent lamp we used in the past would always make noises. Why? It was because of the 50 Hz alternating current. Similarly, the current of nearly 1,000 amperes here will cause very serious vibration cracking and eddy current heating. We have made great efforts to overcome this problem.

▲ Drift tube linear accelerator

There is also a drift tube linear accelerator, which has 156 drift tubes, each one is different, and the installation error is required to not exceed 30 microns, which is very precise.

▲ Target manufacturing companies "go abroad"

Another one is the core target. We have innovative tungsten-tantalum coating technology and process, which has reached the international leading level. The manufacturer of the target body plug-in is Beijing Antai Company. We have successfully developed a very critical target body. This also enabled them to successfully win the bid for the target body of the European Spallation Neutron Source.

▲ Spectrometer construction

These are the three spectrometers owned in the first phase, including a multifunctional reflection spectrometer, a small-angle spectrometer, and a universal powder diffraction spectrometer.

▲ Bird's-eye view of the China Spallation Neutron Source (August 2017)

This is an aerial photo taken in August 2017, taken by a drone without any modification.

When we submitted articles to foreign magazines, we used this photo. They always thought we had synthesized it, but in fact there was no modification. It was so perfectly constructed.

China's Spallation Neutron Source shines in various fields

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▲ The first target shooting was successful, and the neutron beam was obtained in advance

In August 2017, we succeeded in our first target shooting. We got a beautiful neutron beam as soon as we pressed the button. In July of that year, I visited the British Spallation Neutron Source. Before I pressed the button, the British director repeatedly reminded me that I had to be fully prepared. The first time I shot, I might get nothing. He said that they couldn't figure out where the neutron beam went for more than ten days. But our design was reasonable, and the quality of equipment installation and debugging was high, so we got the beam as soon as we pressed the button.

The above are the required acceptance indicators, and the following are the indicators we actually achieved. You can see that the power achieved is more than twice the acceptance indicators. All acceptance indicators have been achieved, and we have successfully passed the national acceptance.

The report of the National Acceptance Committee believes that the design is scientific and reasonable, the equipment quality is excellent, and it has reached the international advanced level. Through independent innovation and integrated innovation, a series of major technological achievements have been made in high-current proton accelerators and neutron scattering, which has significantly enhanced my country's innovation capabilities in these fields and achieved a major leap forward.

Now, we have become the fourth country in the world to have a spallation neutron source after the UK Spallation Neutron Source, the US Spallation Neutron Source, and the Japan Spallation Neutron Source.

The China Spallation Neutron Source has achieved stable and efficient operation. Our power has reached 50 kilowatts, which is half of the design value, and the efficiency of providing beam current exceeds 94%.

After passing the acceptance, a user's article was published in the second month. The US Spallation Neutron Source did not publish any articles in the first two years, which caused a lot of criticism. Our results came out very quickly.

We have now conducted experimental research in many fields, with more than 50 units, including 3 institutions in Hong Kong and the United Kingdom, conducting experiments, and 8 articles have been published.

This is the result of studying superconductors, which have extremely wide applications.

Another is the research on "super steel". The team led by Huang Mingxin from the University of Hong Kong has developed the world's strongest steel. They use a powder diffractometer to analyze the properties of the steel, providing key data for improving the fracture, toughness and corrosion properties of the steel. Super steel is widely used. For example, if a car loses 10% of its weight, it can save 6%-8% of its fuel, so this is a very important field.

In addition, Beihang University and Shanghai Jiaotong University are researching a new type of alloy that can be used in the F-22 landing gear. They have done a lot of research on this using spallation neutron sources.

City University of Hong Kong uses this to conduct research on metallic glass, a material that combines the advantages of both glass and metal.

In the future, it will not be enough to just use the three existing spectrometers. We are working with research institutes and universities in the Pearl River Delta region to build user spectrometers, and the Guangdong Provincial Department of Science and Technology has also donated two spectrometers. Because many materials have residual stress and metal fatigue problems, the only solution is to use a spallation neutron source.

We are applying to the National Development and Reform Commission for the second phase of the project to build more spectrometers and increase its power to 500 kilowatts. It is currently the number one project in the Academy of Sciences' 14th Five-Year Plan, and it may even be launched by the end of this year.

Another is the plan to build a southern light source. Because the governments of the Guangdong-Hong Kong-Macao Greater Bay Area are eager to build a synchrotron radiation source, the combination of spallation neutron sources and advanced light sources is the best match for a large scientific platform.

▲ Plan to build the Southern Light Source

We have reserved 600 mu of land to the west of the Spallation Neutron Source. This picture is a conceptual diagram of the Southern Advanced Light Source, which will play a huge role in the construction of the Guangdong-Hong Kong-Macao Greater Bay Area.

The China Spallation Neutron Source is a project of the 12th Five-Year Plan for National Economic and Social Development. It is the largest single scientific research facility built in our country to date, a "national treasure". It provides powerful research means for my country's materials science, basic physics, chemistry and chemical engineering, life sciences, resources and environment and other fields, and provides an advanced platform for solving bottleneck problems of national strategic needs.

We overcame various difficulties and completed the construction project on schedule. The China Spallation Neutron Source CSNS has become the core large-scale scientific facility in the Guangdong-Hong Kong-Macao Greater Bay Area. Everyone is welcome to visit the Spallation Neutron Source!

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