Superconducting magnets have been used in the industry. The most glaring example of their use — Magnetic resonance imaging (MRI). But the possibility of superconducting magnets could be greater if it were possible to solve a number of technical problems over which successfully work at the Kurchatov Institute, together with Academician VNIINM Bochvar.
The staff of the Kurchatov Institute, engaged in the development of the method of stabilization of superconducting magnets with VD. From left to right: I. Kovalev, AA Ilyin, VE Keilin, AV Naumov, SL Kruglov, DI Shutova. Photo courtesy of Victor Keylina
Superconductors in the technique
Despite the fact that superconductivity was discovered exactly 100 years ago, in 1911, over half a century, it remained only amusing physical phenomenon that bears no practical use. The situation changed dramatically with the discovery of superconducting niobium-based materials — NbTi, Nb3Sn, capable of carrying high currents without destroying the superconducting state. The magnetic field produced by conventional electromagnets limited enormous heat release in the coil during the flow of large currents. The operation of such devices is obtained unreasonably expensive because of the constant need for cooling, and a lot of energy.
A superconducting magnet (SM) due to the absence of electrical resistance almost does not consume electricity and, most importantly, allows you to get the fields are inaccessible to conventional materials. It can only operate at low temperatures, but to date methods of cooling CM is well developed. Moreover, with the advent of compact devices — cryocoolers, which give helium temperature ~ 4 K (269S), without any liquid refrigerant, the cost of the actual cooling of the magnetic system are slim. Now CM is widely used in medicine, industry and, of course, scientific instrumentation. Russia is planning to acquire magnetic resonance tomography own production and even go out with them on the international market, and for this it is necessary to solve a number of technical problems CM.
The design of advanced composite superconductors is quite complex and represents thousands (sometimes tens of thousands) of thin superconducting fibers placed in a copper matrix. The growth temperature of the superconductor under the influence of even small thermal pulse is entirely determined by only the heat capacity of the composite. At liquid helium temperatures, the heat capacity of conventional construction materials are very small (in the hundreds or even thousands of times lower than the values at room temperature), so even a slight heat may be enough to heat the superconductor above the critical temperature, which is accompanied by an uncontrollable transition CM to normal and sometimes even burn parts of its winding. Similar happened at the Large Hadron Collider, which stopped his work for a long time.
One way to solve this problem and improve the reliability of the SM — Add to the superconducting material substance with a high heat capacity. This way, went to the Kurchatov Institute. They experimented with vysokoteploemkimi additives (VD) whose specific heat in the temperature range 4-10 K because of various quantum effects in hundreds times higher than the conventional materials.
As additives improve the properties of the SM
To learn more about the new development of the Kurchatov Institute, I met with one of its authors — head of the Laboratory of strongly correlated electron systems Vladimir Lazukovym. First of all, I wondered how HP can improve the properties of magnets.
— The fact that we introduce in the CM additives having a high specific heat at extremely low temperatures can increase the overall heat around the superconductor and thereby create a thermal buffer — explains Vladimir Lazukov. — So to translate the superconductor to the normal state requires 2-3 times more heat than conventional magnet with no additives.
As rare earth materials, which does your laboratory, can be used in the SM?
— Electronic systems based on rare-earth materials have completely abnormal properties. For example, cooling can both expand and contract, the magnetic moments in some of them, instead of order at the temperature may disappear. In addition, in the liquid-helium temperatures (4-6k), due to the strong electron correlations in them there is an additional, very large contribution to the heat capacity. This effect we have proposed to use for the stabilization of superconducting magnet systems. The practical test of this idea was carried out under the guidance of a team of Victor Keylina.
Perhaps production SEE with such additives will be much more expensive?
— Not at all. Thermal stability will allow the use of less expensive superconductors to create the SM and expend less energy to cool them, and the increased thermal magnetic stability will lead to the use of cheaper conductors having a smaller number of larger cross-section of the superconducting filaments. This improvement in the quality of the wires more than offset a slight rise in the cost of production due to the introduction of high pressure. Moreover, it may lead to increased use of superconductors and competitiveness of Russian CM in the world market.
According to project leader Viktor Keylina, improved superconductors will be used in the manufacture of magnetic resonance imaging — the most commercialized of the related field of superconductors. So far the only way for Russia to world markets CM — participation in the international fusion project ITER, under which our country must be shipped hundreds of tons of superconducting wires. However, to improve anything in this cable is too late — it would require changing all the arrangements.
It must be in the world have been attempts to create such a technology …
— We are working with this subject since the beginning of the 2000s, we have three patents. When just beginning to develop the technology, it seemed that the increased stability of superconductors by 10-15 percent will have great success. This would be a way out to the world level these technologies. The experimental results have exceeded expectations — it was possible to increase significantly. In this sense, our proposal is innovative.
At what stage is your job?
— Extensive research and laboratory tests performed at the Kurchatov Institute, demonstrated the advantages of the proposed method. In VNIINM Academician Bochvar under the leadership of Alexander Shikova, currently heads the work on superconductivity at the Kurchatov Institute, has presented technology for producing prototypes superconductors doped with an internal HP with typical lengths of several hundred meters.
— Usually the study of superconductors we hold the initiative in its own budget — said the first deputy director of the Kurchatov Institute Yaroslav Shtrombakh. — However, this work we proposed concern fuel elements, which financed it.
According to the developers of the method, the next step should be the introduction of new technology in industrial production, including for the creation of an MRI. Negotiations with Chepetsk Mechanical Plant in Glazov, specializing in industrial production of low-temperature superconductors. However, this major step will require significant financial cost
— We hope that the corporation TVEL will go to these costs, because they will pay off in demand for home-temperature superconductors in the world market, — said Victor Cailin. — But we can not completely rule out the pessimistic variant — funds for commercialization of superconductors with HP will not. Then, perhaps, in spite of our patents, production of the wires will be disbursed abroad. Humanity wins and Russia?
Author material: Fairy Oleg