The staff of tIhe Department of Electrophysical Installations of the Institute of Nuclear Physics and Technology of the National Research Nuclear University MEPhI is currently actively involved in the creation of various accelerator installations. They are helping the Kurchatov Institute to create the SILA accelerator complex, and are involved in the creation of an electron accelerator for the Institute of Applied Physics of the Russian Academy of Sciences. MEPhI, together with Rusat Healthcare, is also developing a medical accelerator and its own research accelerator, which will be located at MEPhI. Andrey Batov, a graduate student at the Department of Electrophysical Installations, talks about all these works. The conversation took place within the framework of the "Voice of Science" section.
It is important to note that the department's projects are quite large-scale. Our department has 8 laboratories that allow us to fully cover the accelerator – control systems, power systems, vacuum systems, beam dynamics calculations, calculations and production of an accelerating structure. And, of course, the mechanical part. It is also important to place and secure the installation correctly, as well as to calculate its parameters correctly. In all this diversity, I am engaged in modeling geometry and controlling the production of accelerating structures. I participate in the launch of the resulting accelerators. I'll tell you about the projects I'm involved in. Besides them, there are many others at the department, but I think it's better to tell those who deal with them.
Cannon for the SILA complex
For the Kurchatov Institute, MEPhI is making a photo cannon, a photoemission source of electrons. It has already been manufactured, soldered and is being tested at our department. The development is carried out by a large team of staff of the department, headed by the head of the department, Sergey Markovich Polozov. The main work on the accelerating structure is performed by Ilya Ashanin, Roman Zbruev – engineers of the department, Mikhail Vladimirovich Lalayan – associate professor of the department. I was partially involved in her calculations and in the production control process. During production, a rather serious accuracy was needed - about 10 microns. Inaccuracies happen in real production, and it was necessary to resolve issues related to the appearance of deviations on the spot. We successfully coped with this, and the first cold tests showed that the measurements were consistent with the calculation. Of course, there were also difficulties in the calculation, because this is a relatively new field of accelerator physics. There are similar camera guns now in Germany, the USA and Japan, there are still quite a few of them, there is little experience in their manufacture in the world, therefore each such product is unique.
What is the uniqueness?
Nowadays, thermionic sources are almost universally used as a standard source of electrons. This is when you, roughly speaking, heat a wire in a light bulb and electrons fly out from there under the influence of thermal emission. But in our case, the principle is radically different, here is photoemission, that is, you shine a laser on the photocathode. Photocathodes are made of different materials, and we have a separate employee, Mikhail Vladimirov, who is engaged in the physics of photocathodes, because a whole science is built around this - how to choose the right photocathode with the right characteristics. There is not even a generally accepted theory of how the photoemission process from semiconductor cathodes actually works, since the accepted Fowler-Nordheim theory is taken from autoelectronic emission and works well for metallic photocathodes, but it does not converge at all with experimental results for semiconductor ones.
In addition to the interaction of the laser and the photocathode, the photocell has a microwave part that intensively accelerates the beam resulting from photoemission. This installation is practically a small linear accelerator. As a result, extremely small beam sizes are obtained, which are unattainable with thermionic guns. Such parameters are needed for modern radiation sources – free electron lasers.
Synchrotron installations have historically been divided into generations based on the brightness of synchrotron radiation. When it was discovered experimentally, it was just a side effect of the annular acceleration of charged particles; but then they realized that it could be used as a microscope. If you look through a light microscope, the resolution is on the order of a micron, that is, 10 to the minus sixth power of a meter. And on modern synchrotrons, the resolution is about 10 to the minus tenth of a meter. But to achieve this resolution, you need a beam of fairly hard high-brightness photons with precision parameters. And this cannot be achieved with conventional thermionic sources. This is exactly what photoelectronic sources are interesting for.
At high frequencies
A lot depends on the energy level at the output of the photo cannon. The photo cannon for the "Force" is designed for high energy, for Nizhny Novgorod - for less. Plus they work on different frequencies. Historically, camera guns have evolved from lower frequencies to higher ones. The Japanese and Germans make electron sources at relatively low frequencies – 1300 MHz. The class of our photo guns that we produce here is designed for high frequencies - 2.4-2.8 GHz.
If you increase the frequency in the accelerating structure, you can achieve a higher rate of acceleration, and thus you solve a lot of problems in connection with the achievement of relativistic speeds by electrons. Until the electrons have converted to relativism, there are a number of effects that interfere and need to be overcome. The faster you put the electrons into relativistic mode, the better off you are as an accelerator operator. This is easier to do on higher frequency structures — this is the first point. The second point is the size of the installation. The lower the frequency you have, the bigger the installation is physically. The higher the frequency, the more compact you can make an accelerator with the same energy.
Nizhny Novgorod diamonds
The Institute of Applied Physics of the Russian Academy of Sciences in Nizhny Novgorod is making an electron accelerator, which also needs a photomunner, but with a different energy. This is also a research accelerator, but for slightly different purposes. An important advantage of the IPF RAS is that they are the only ones in Russia who can make diamond photocathodes. All the others use, for example, copper ones, the efficiency of which is much lower. Later, they will supply diamond photocathodes to the Kurchatov Institute, but with the help of their camera cannon, they will, in particular, check how good their photocathodes are and will be engaged in their further improvement. This is probably the first time the camera cannon will be on our Russian photocathode. For them, a small research camera is being made with one and a half cells against a three and a half Kurchatov camera. Nizhny Novgorod will have a relatively small linear accelerator itself, consisting of only one section with 20 cells at about 20 MeV versus an accelerator with 40 sections with 6 GeV for SILA. We have already produced the regular part of this camera cannon and transferred it to Nizhny Novgorod. The project is led by Sergey Markovich Polozov, Head of the Department. Ilya Ashanin, Roman Zbruev, Mikhail Vladimirov, graduate students and engineers of the department, and Mikhail Vladimirovich Lalayan, associate professor of the department, regularly performed the main work on the accelerating structure. I participated in the calculation of the accelerating structure and the control of its manufacture. My colleagues and I from the IPF RAS are currently in the process of working on the design documentation for the electron source of this cannon. Nikita Samarokov, an engineer and graduate student of the department, is also the main developer of the electron source.
MEPHI against cancer
We are developing a medical gamma radiation source for the irradiation of cancerous tumors. Those that are currently used in Russia are all imported. They are made by companies such as Varian, Elekta, and many other manufacturers, but such machines have not been mass-produced in Russia. The Russian version is currently being developed by MEPhI together with JSC Rusatom Healthcare. We are making an accelerator for them and everything related to the accelerator, that is, calculating the dynamics, calculating the characteristics of the accelerating structure, and the control system. MEPhI is also responsible for manufacturing, soldering and launching the accelerator. Rosatom is responsible for the power supply and the frame, as well as for the management of the complex as a whole and medical aspects – radiation planning, patient positioning, the collimator system, and so on. The principle of operation of the electron source of this accelerator is thermionic. This is a microwave linear accelerator based on a biperiodic accelerating structure, the so-called LINAC. It operates at a frequency of 2800 MHz. Accelerates electrons from the energy set in the electron source to 6.3 megaelectronvolts. At the same time, it is very compact, it will literally fit on the table. Compactness with high values of acceleration structure characteristics is one of our achievements in this project. The main work on the accelerator part was performed by Roman Zbruev and Nikita Samarokov, engineers of the department. Lalayan Mikhail Vladimirovich is an associate professor of the department. Raschikov Vladimir Ivanovich, an associate professor at our department, has developed a unique, very compact electron cannon for this accelerator. I participated in the calculation of the accelerating structure, the control of manufacturing, and the physical launch of the accelerator. We would like to thank our industrial partner NPP Korad for providing a testing site and assistance in conducting them.
Radiation at the customer's choice
For its own research, MEPhI is currently building a two-section accelerator for applied applications, for example, for work on the radiation resistance of an electronic component base. It will be located in the new bunkers of the MEPhI Accelerator Center, which will be located in a renovated hangar on the university grounds next to the garages. Research customers will be able to work with both an electron beam and a gamma ray. The installation will be distinguished by the original design of the target node and a very clever focusing system, which will allow you to obtain a square beam with a uniformity in flux density of better than 20%. Until now, users have not had the opportunity to use such beam profiles. In addition, this installation will have the highest efficiency and the highest beam current among accelerators of this class at the moment. This will ensure high repeatability of the results in research, and a high rate of sample change, high radiation doses, which in turn means that we will be able to allow more users to use this installation - more than the analogues that currently exist.
The equipment for this accelerator is also ready and is located at our department. This accelerator can be used to sterilize medical equipment and products, as well as to test electronics for radiation resistance. For example, to test electronics installed in orbiting satellites. Charged particle accelerators are also used to simulate cosmic radiation, which make it possible to see how much the electronics on the satellite will be resistant to near-Earth space conditions.
UMNIK – Electronics design team
In December 2023, a team of young specialists from the department and I won the UMNIK grant in the amount of 3,000,000 rubles. Besides me, the team includes graduate students Nikita Sumarokov, Roman Zbruev and Yakov Abakumov. The scientific supervisor of the project is the leading engineer of the department T.V. Bondarenko. The project topic is "Development of an electron source for a medical accelerator with a stand for alignment and tuning." The essence of the work is to develop an import-substituting electron source for foreign radiation therapy systems and a stand where any thermal emission guns can be tested. At the moment, we are in the final stage of the project. The stand and the electron source are in the testing process at the department. My role is the head of the project team and the development of the booth management system.
Interviewed by Konstantin Frumkin, MEPhI Press Service
