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MOSCOW, May 13 – RIA Novosti, Tatiana Pichugina. The successful construction of an X-ray free-electron laser – XFEL – has generated worldwide interest. Few people know that this project has Russian roots. XFEL will be able to photograph structures smaller than a nanometer and thus solve many practical problems for biology, chemistry, medicine, and materials science. The inventor of this installation – Eugeny Saldin, now a member of DESY (Germany) – told RIA Novosti about the principles of its work and the opening of scientific perspectives.
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X-ray radiation is used to study the structure of molecules for almost a hundred years. This is facilitated by a small wavelength of this part of the electromagnetic spectrum – on the order of one angstrom (one-tenth of a nanometer). Photons simply dissipate on the crystal lattice and create a diffraction pattern on the detector, through which the three-dimensional structure of the molecule is reconstructed using software. As early as the middle of the 20th century, the X-ray helped to understand how DNA was constructed.
Earlier, scientists used X-ray tubes, now they have at their disposal X-ray sources of great brightness, which is formed in ring electron accelerators – synchrotrons. Therefore, radiation is also called synchrotron radiation.
A bunch of electrons in the ring accelerates to near-light speeds, emitting photons with different wavelengths – up to the x-ray range. It is taken to the channels where the samples are irradiated, and the radiation detectors record data on the atomic structure of the molecules. Dozens of different experiments can be performed during the session.
If in the path of the electron bunch, which rotates in the ring, to establish a series of strong magnets – undulators that turn the trajectory into a sinusoid, the quality of the accompanying radiation can be increased many times.
A powerful linear accelerator instead of a synchrotron makes it possible to form a bunch of electrons of very high density and of excellent quality. In a long undulator, its radiation affects the electrons, amplifies and proceeds with very short impulses, turning, in fact, into a laser of enormous intensity. Theoretically, all of its energy can be concentrated in a spot of diameter on the order of the wavelength – one tenth of a nanometer. This is XFEL. And the phenomenon of self-amplifying spontaneous emission, underlying it, was discovered in 1980 by Soviet physicists from Novosibirsk Anatoly Kondratenko, Yaroslav Derbenev and Yevgeny Saldin.
© Photo: Helmholtz-Zentrum Berlin
Yevgeny Saldin graduated from the Physics and Mathematics School at the Novosibirsk State University, and later the Faculty of Physics. He joined the Accelerator Laboratory of the Institute of Nuclear Physics in Akademgorodok.
"There was a great desire to do science, but it was realized only in 1977, when I started working together Yaroslav Sergeyevich Derbenev and Anatoly Mikhailovich Kondratenko, whom I consider to be my teachers", – tells RIA Novosti Eugene Saldin.
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That year in Stanford, the first free-electron laser (FEL) with a wavelength of three microns was activated – and Novosibirsk scientists connected to this direction. But if the majority of physicists around the world worked in the optical range, trying to maximize the brightness of the beam, then Seldin and his colleagues decided to create a FEL in millions of times more powerful and focused on the x-ray range.
"At that time, our work looked like science fiction. The reviewer from the journal Nuclear Instrument and Method Journal wrote in a response to the article that it was all "science fiction". And he added: "But who knows what will happen in twenty years?". Therefore, the publication took place", The scientist continues.
Publications in foreign journals brought Saldin world fame. He gathered around him a group of young enthusiasts and for the next ten years developed a theme that in 1999 ended with the monograph The Physics of Free Electron Laser.
The subsequent development of physics has shown the rightness of Novosibirskians. Quantum lasers quickly replaced FEL in the optical range. In contrast, free-electron X-ray lasers (XFELs) with high gain have become popular all over the world, despite their large size and cost. Over the past two years, XFEL was commissioned in Germany, South Korea, Switzerland.
© RIA Novosti / Yuri Sagittarius Go to the photobank
In the 1990s, the DESY Research Center for High Energy Physics near Hamburg planned to build a linear electron-positron accelerator 30 kilometers long with half teelectronwolt energy – TESLA. However, the work was canceled in connection with the closure of the national program on high-energy physics. All research in this direction was transferred to CERN.
A similar conversion of national programs on high-energy physics was undertaken by other EU countries. Having the powers and means collected from the participating countries, at CERN they decided that in the next two decades they will concentrate on the Large Hadron Collider and will not build a linear electron-positron accelerator.
In order to preserve scientific schools and employees, DESY was reoriented to an X-ray laser, for which a linear accelerator was required, and not a ring accelerator, and TESLA developments could be used. The inventor of XFEL Yevgeny Saldin was invited in 1994 to create a prototype, and already in the beginning of 2000 the TTF1 X-ray laser at a wavelength of 80 nanometers successfully earned, immediately showing the unique possibilities of studying atoms and molecules.
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This installation literally saved the DESY center from the closure and helped to overcome a difficult period of change of scientific specialization. Although not everything went smoothly. Believing in the success of TTF1, the German government conceived the idea to build the most powerful X-ray laser in the world together with other EU countries. The budget of the project amounted to one billion euros. Germany immediately contributed 500 million euros. But with co-financing difficulties arose.
According to the law, construction can be started only if the project accounts have 75% of the budget. German Chancellor Angela Merkel was in a deadlock: to create the world’s first XFEL was a matter of honor, but the project stalled. The situation was saved by Russia, which made in 2009 250 million euros. After that the project started.
The delay in financing cost Europe a priority. The first XFEL was launched by the USA (LCLS installation in Stanford) – and in 2012 it was deciphered with its help the structure of the protein causing African sleeping sickness. However, Yevgeny Saldin does not consider this a major scientific breakthrough. In his opinion, protein structures are deciphered on sources of specialized synchrotron radiation (ISSI) approximately two thousand per year. In all, about one hundred thousand structures of more than two hundred million have been determined at the moment.
Another matter – the decoding of all biologically active protein structures. It is impossible to do this on ordinary ISSI. To investigate the biomolecule, it is necessary to turn it into a crystal. But only a small part of the proteins lends itself to this procedure. The problem is that the crystal must be large enough. Dimensions were reduced thanks to the latest generation of ISSS, which somewhat expanded the range of proteins studied, but the limit had already been reached.
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"When photons are scattered on a sample, their absorption takes place, which destroys the molecule long before the necessary information is carried away by the scattered radiation. Then a new method was proposed – diffraction before distruction (diffraction to failure). You can only apply it to XFEL", – Yevgeniy Saldin explains.
In Stanford, for example, it was possible to reduce the size of crystals to ten microns and fit them to tens of thousands of protein molecules.
"This expands the range of proteins, the structure of which can be deciphered, but insignificantly", – emphasizes the scientist.
A cardinal solution to the problem is to determine the structure of the protein by one molecule without crystallizing it. This requires a more perfect laser. The pulse of X-ray radiation is needed so short – about five femtoseconds – that the electrons do not have time to leave the molecule of the substance under study. Then the detector will receive an undistorted picture of the molecular structure. In this case, each pulse must contain enough photons, which means that the peak power of the laser should be increased to terawatt.
"This is the most important task for the X-ray range, which we solve on the European XFEL. In the future, we will increase the number of photons in a short pulse by a factor of 100 compared to LCLS. Now the molecule is injected into the detector and the software is being improved, which, like in the tomography, is of decisive importance", Says Saldin.
A new technique, developed in DESY, will allow in a few hours to decipher the structure of any protein. This will promote very rapid progress in biology and medicine, comparable to the decoding of the human genome.
© Photo: XFEL
In the world there are about 60 ISSS of different generations. Two of them are in Russia: in the Kurchatov Institute in Moscow and INP SB RAS in Novosibirsk. According to Yevgeny Soldin, for such a large territory it makes sense to create at least three third-generation installations, which are synchrotrons with multiple X-ray emission channels. The construction of such sources in the world is well-developed. Recently, their brightness has been significantly improved due to magnets of a special configuration. These modernized sources have recently been called ISSI-4.
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Construction takes three to four years, while unlike linear accelerators, underground tunnels are not required. Up to 80 percent of the budget goes to the creation and equipment of the path of the electron beam. It is unlikely that it will be possible to manage only Russian materials and equipment, something will have to be ordered abroad. At the same time, superconducting magnets for the undulator are excellent in Novosibirsk. In addition, in the process of construction and operation of ISSI around it will be a lot of commercial firms, where it will be possible to place orders for parts and services.
According to the scientist, the construction of ISSI is a world trend, capable of satisfying a huge request from biologists, physicians, chemists, and materials scientists. After this, having experience and frames, you can go to XFEL (which, strictly speaking, is incorrectly called ISSI, since the source of radiation is not a synchrotron, but a linear accelerator). It will automatically pull the rapid development of various branches of science and industry.
For example, in DESY around XFEL there is a center for decoding the structures of biomolecules, creating a center for infectious diseases on the basis of ISSI PETRA and EXFEL, femto- and nanocenter, centers for transfer of technology.
"As practice shows, there is no military application of such installations and is not foreseen. The only project that is being implemented is a free-electron laser in the optical range with mirrors. And at a specially selected wavelength, as water vapor absorbs strongly in all other ranges. Conventional quantum lasers can not cope with this task. The works go to Jefferson Lab, located near the US Naval Base. Perhaps in the next decade the FEL will be ready for installation on an aircraft carrier", – the researcher notes.
© RIA Novosti Illustration
In the opinion of the scientific community, the invention is quite worthy of the highest scientific award – the Nobel Prize in Physics, as it marks the mastering by mankind of the X-ray range.
No wonder that in 2015 the Nobel Committee organized a symposium on XFEL. With the reports on it were three contenders for the award: American physicist John Meydi (John Madey), the creator of a free electron laser (died last year), Eugene Saldin, XFEL X-ray laser inventor, and Claudio Pellegrini, the initiator of the world’s first installation of this type (LCLS in Stanford).
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"It was not possible to break through to the X-ray range with the help of quantum lasers for about forty years, although the total amount of money spent on this was enormous. The maximum that could be achieved is a wavelength of ten nanometers. And XFEL gave one-tenth of a nanometer in ten years. This achievement can be compared to a geographical discovery that occurs only once in the history of mankind. Of course, the size of the installation is still large, but the development of the radio range also began with tube receivers, and now everything is miniaturized thanks to semiconductors", – concludes Yevgeny Saldin.