Hard X-ray free electron laser device can make movies for molecules

Recently, as a priority of the “13th Five-Year Plan for National Major Science and Technology Infrastructure Construction”, the hardest X-ray Free Electron Laser Device (XFEL), the largest investment in science and technology infrastructure in China, has been approved. This kind of device is called "high-speed camera" by scientists called "Nature" magazine because it can help scientists to see the microscopic world on the atomic scale and even on the electronic scale.

Since the movement of atoms and electrons is too fast, humans have never seen how they move. XFEL can capture the instantaneous images of the microscopic world, and can be played back slowly, allowing scientists to understand the mysteries. It has become a scientific research tool developed by various countries.

The hardest X-ray free electron laser device (XFEL), the largest investment in science and technology infrastructure in China to date, has recently been approved. The site is located in the core area of Shanghai Zhangjiang Comprehensive National Science Center. The 3.1-kilometer-long unit will build an underground tunnel with a depth of about 30 meters, along the Luoshan Road in Pudong New Area, and extend to the Shanghai University of Science and Technology Park.

As early as 2009, the United States built the world's first XFEL. In recent years, Japan, Switzerland, and South Korea are stepping up their research and development. In September last year, the 12 European countries jointly invested 1.2 billion Euros and built the first batch of experiments in Europe XFEL near Hamburg, Germany.

The X-rays provided by the hard X-ray free electron laser device can be tens of thousands times brighter than the third-generation synchrotron radiation source, helping scientists to see the atomic world and even the microscopic world on the electronic scale. Taking "molecular photos" to the level of "molecular film" has become a hot spot for scientists around the world. The British magazine Nature called this device a "high-speed camera" for scientists.

Ultra-fast time resolution than ordinary X-rays

When a high-speed moving electron is deflected by a magnetic field, it emits synchrotron radiation in a tangential direction, which is 10,000 times stronger than ordinary X-rays. X-ray free electron lasers are stronger than synchrotron radiation, which is a laser that emits high-energy electrons in the forward direction when subjected to a magnetic field.

X-ray free electron laser is divided into soft and hard X-ray according to different energy and wavelength. The latter has higher brightness, tens of thousands times higher than synchronous radiation, and its wavelength can reach several nanometers (10 meters).

Compared to synchrotron radiation, X-ray free electron lasers have higher brightness, shorter pulse structure, and better coherence. Synchrotron radiation can see the molecular level structure, while hard X-ray free electron laser can see the atomic level structure. What is the difference? If synchrotron radiation can see the surface of a building, then a hard X-ray free electron laser can see what's going on in each window.

Obviously, XFEL can help scientists see the microcosm that they have never seen before, and some scientific speculation may solve the mystery. Although there is still much room for improvement in the existing XFEL performance, scientists have used this super-light source to get some new discoveries. For example, the international cross-team led by researcher Huaqiang Xu of the Shanghai Institute of Materia Medica, Chinese Academy of Sciences, through joint research, successfully analyzed the phosphorylated rhodopsin and repressor complexes using XFEL from the Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory. The crystal structure has overcome major scientific problems in the field of cell signaling. With the improvement and improvement of data analysis methods, he used the same set of data and had two major discoveries. The papers were published in the American magazine Cell. This also illustrates from one side that XFEL will bring valuable research data to scientific discoveries.

In the past ten years, scientists around the world have been pursuing this kind of laser and constantly improving its performance, hoping to promote human understanding of nature more deeply. Just last September, the XFEL, which was jointly invested by 12 European countries, began its first experiments near Hamburg, Germany, with an energy of 17.5GeV (109eV) and 27,000 pulses per second. The XFEL energy built in the United States in 2009 reached 14.5GeV, and now it is starting to build an upgraded version. Although the energy index is 4GeV, it can emit 1 million pulses per second, which is 10,000 times that of the current device. China's newly launched XFEL energy is 8GeV, which can produce very high quality photons. It will also have nano-scale ultra-high spatial resolution and femto second (10-second) ultra-fast time resolution.

What can scientists do with hard X-ray free electron lasers? In the early XFEL, scientists could collect about 100 X-rays per second, and at the newly-launched European XFEL station, scientists could collect more than 3,000 high-quality X-rays per second. So, if the number of pulses is up to one million, how many microscopic images of the microcosm will be brought to the scientist?

It is well known that a 24-frame image per second can form a visually continuous motion picture, that is, the most basic movie. When the image per second exceeds 1000 frames, it enters the level of a high-speed camera. Millions of pulses per second mean that there are probably as many as 100,000 X-rays per second, which is truly a super-high-speed camera.

In general, the image quality of high-speed cameras is not very high, but the current resolution of the XFEL high-speed camera has reached the level of 100 nanometers, and will sprint to the nano level in the future.

Why do scientists need such high-speed HD cameras? That's because the movement of atoms and electrons is too fast. Humans have never seen how they move. They can only see a cloud of electrons—the trajectory fog formed by the rapid movement of electrons. It is like martial arts. In the novel, there is a colorful palm, a cybernetic net, or a shadowless god fist. XFEL is expected to capture this process and let scientists play back slowly, to clarify the mysteries of the process, and to clearly see the dynamic changes of electrons and atomic structures, such as how electrons run from one molecule to another. It is equivalent to presenting the micro world in front of people, and this is still not possible at present.

The new discovery will likely subvert many of the previous scientific cognitions, because we can only see vague images now, and we can only use the average image to guess the real microscopic particle world. For example, how does superconductivity occur, how "life machine" protein molecules work, how chemical bonds form in chemical reactions, and so on. Scientists have used this light source to knock out electrons from the iodine atom in the methyl iodide molecule (CH3I) almost completely, so that the iodine atom attracts methyl electrons like the electromagnetic of a black hole, and its response time is at the femto second level. The findings were published in the British journal Nature in June last year.

Since the free electron laser emits light in the direction of electron advancement, it cannot draw a beam of light around a large ring like synchrotron radiation, and builds dozens of experimental line stations, but only allows light. Slightly deflected, divided into a limited number of bundles, connected to the experimental station (the number is generally no more than ten). This also makes it particularly valuable.

General XFEL includes linear accelerator tunnels, undulator tunnels, beamline tunnels, and user devices. In order to obtain higher energy electrons, a longer electron acceleration distance is required, so the device will be longer and longer. In order to shorten the distance of electron acceleration, a superconducting-based accelerator is becoming the mainstream of XFEL construction in the world.

XFEL, which is about to be built in Shanghai, also uses superconducting accelerators to become one of the most efficient and advanced free electronic laser user devices in the world.

After the installation, the device will provide cutting-edge research methods such as high-resolution imaging, ultra-fast process exploration, and advanced structural analysis for physics, chemistry, life sciences, materials science, and energy science. The Zhangjiang area will also become an international photonics research highland in the same area with a cluster of synchrotron radiation sources, soft X-ray free electron lasers, hard X-ray free electron lasers and ultra-strong ultrashort lasers.

The project will also try to break the walls of universities and research institutes, join hands with a large number of high-tech enterprises, and “gather strengths to do big things” in the Zhangjiang area. The reporter learned that because many technologies of XFEL must challenge the limits, it will have a significant traction effect on the improvement of China's high-end manufacturing industry.

Use of hard X-ray free electron laser

XFEL's first experiment

Free electron lasers begin with the discovery of atoms. The research was published in the July 1st, 2010 issue of the British journal Nature.

Study proteins that are difficult to crystallize

The international cross-team led by Huaqiang Xu, a researcher at the Shanghai Institute of Materia Medica, Chinese Academy of Sciences, has solved the problem of cell signaling by using the crystal structure data of phosphorylated rhodopsin and repressor complexes analyzed by the world's strongest X-ray laser major scientific problem. The breakthrough achievement was published in the American Journal of Cell on July 28, 2017 as a cover story.

See the atomic structure

The extremely high-intensity X-ray free electron laser knocks 54(62) electrons out of the iodine atom (right) of the methyl iodide molecule CH3I, making it attract the methyl (left) electrons like the black hole electromagnetic, and its response time is within the femto second. The study was published in the British journal Nature on June 1, 2017.

Reveal the mechanism of chemical reaction

Capture the moment of formation of chemical bonds. The research results were published in the February 12, 2015 issue of the American journal Science.

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