One of the most important structural elements of a tokamak is a vacuum discharge chamber, which satisfies specific requirements concerning the induction method of plasma generation and, accordingly, the presence of alternating magnetic fields additionally acting on the chamber. Moreover, the chamber should not only be able to create and confine a current plasma but also be able to diagnose its parameters through appropriate pipes. The small spherical tokamak being created at MEPhI for both educational and research purposes has an extensive program of such studies; therefore, the discharge chamber should not only allow fast evacuation and withstand alternating magnetic fields but also be convenient for measuring its parameters, using various diagnostics, as well as allow quick replacement of internal elements and introduction of additional power into the chamber. The paper describes the design of the vacuum chamber of the MEPhIST-1 tokamak, which meets these requirements, and presents calculations to justify the choice of material and the thickness of the characteristic elements of the chamber, and also presents the test results of the finished chamber.

We have measured the temperature dependence of the resistivity and magnetization of a special steel of the Fe–Cr–Ni austenite–martensite class in a wide temperature range (77–1100 K). It is found that at temperatures 77–170 K, the resistivity of the material almost remains unchanged, but upon a further increase in temperature, the resistivity sharply increases, which is probably a result of disordering. In addition, anomalous behavior of resistivity with vanishing spontaneous magnetization is observed at 910 K, which is associated with the ferromagnet–paramagnet phase transition. Comparison of the measured ρ( T ) dependence with the analogous dependence for 12Kh18N10T austenite stainless steel has not revealed features typical of Fe–Cr–Ni steel.

AbstractWe have measured the temperature dependence of the resistivity and magnetization of a special steel of the Fe–Cr–Ni austenite–martensite class in a wide temperature range (77–1100 K). It is found that at temperatures 77–170 K, the resistivity of the material almost remains unchanged, but upon a further increase in temperature, the resistivity sharply increases, which is probably a result of disordering. In addition, anomalous behavior of resistivity with vanishing spontaneous magnetization is observed at 910 K, which is associated with the ferromagnet–paramagnet phase transition. Comparison of the measured ρ( T ) dependence with the analogous dependence for 12Kh18N10T austenite stainless steel has not revealed features typical of Fe–Cr–Ni steel.

316L stainless steel powder was used for volumetric laser cladding. We studied the microstructure of obtained objects, diffusion processes of the substrate components and the metal of laser cladding. Various strategies of layering metal powder were offered and mechanical tests of the samples properties were performed.

The target of this work is the demonstration of advanced novel approaches able to provide rapid prototyping by using laser technology ceramic MEMS platforms for chemical sensor operating under harsh environmental conditions and, on the other hand, to assure microhotplate stable at high temperature, which can be used for the deposition of high working temperature gas sensing materials, for example, oxides of tin, gallium, zirconium and hafnium. As substrate ceramic material in work using alumina oxide.

The effect of cyclic laser heating on the formation of the austenite structure in the austenitic-martensitic alloys based on Fe-Cr-Ni system is investigated. It is shown that under the influence of ultra-fast laser heating on the martensite, which was formed during plastic deformation, the reverse martensitic transformation occurs, and austenite with high strength characteristics is formed. Repeated and multiple laser heating effectively grinds areas of austenite to a size close to the large nanoparticles. There is an additional increase in the strength characteristics of austenite as a result of this fragmentation.

Samples for tensile tests were manufactured by using one of the additive technologies - direct laser material deposition. Investigations were carried out at the facility Huffman HC-205 equipped with a fiber laser with a power up to 3.5 kW. Various strategies of layering metallic powder of stainless steel 316L were considered to optimize the modes of constructing the samples. We measured the stress-strain state of the produced samples by the method of digital image correlation. It is found that the nominal tensile strength of the samples produced by the direct growing using laser powder of 316L steel is of high level - 767 MPa.

Main technological parameters of heat treatment of ferromagnetic alloy samples of special stainless steel were experimentally determined in order to create the paramagnetic zone of a given size there.

Fabricated and investigated samples of multilayer cladding on the flat surface are obtained using a laser cladding technology. Iron-based powder was used in the study. Geometric parameters of track depending on the process parameters were determined. The effect of thermal fields on the quality of the coating was analyzed. Optimal strategy areas adjacent to tracks and each subsequent layer deposition have been identified. Microhardness of the resulting coatings was measured. Result of this work is a multi-layer coating in order to restore and improve the surfaces of parts, which exposed to wear.

This work is devoted to the research of welding plume during high power ytterbium fiber laser welding of a titanium alloy in the Ar shielding gas environment. High speed video observation of a vapor-plasma plume for visualization of processes occurring at laser welding was carried out. The coefficient of the inverse Bremsstrahlung absorption of laser radiation is calculated for a plasma welding plume by results of spectrometer researches. The conclusion deals with the impact of plasma on a high-power fiber laser radiation.

The features of a laser cladding of nickel-based powders with TaC nanopowder additives have been experimentally investigated. The minimum depth of pro-melting of a basis, microhardness distribution over the cross section of the substrate, and the saturation of the metal of the cladding with basis components has been determined in the experiments.

The possibility of the use of laser radiation heating for making materials with specified distribution of ferro-and paramagnetic domains is studied. It is shown that application of plastic deformation with a high degree or reduction combined with subsequent laser heating in a specified temperature range to austenite-martensite alloys based on the Fe – Cr – Ni system produces materials with required distribution of regions of ferromagnetic martensite and paramagnetic austenite. The modes of laser treatment providing maximum strength of the formed austenite are determined.

Экспериментально исследованы особенности лазерной наплавки порошков на основе никеля с добавками нанопорошка TaC. В процессе экспериментов были определены минимальная глубина проплавления основы, распределение микротвердости по сечению подложки, насыщение металла наплавки компонентами основы.

The effect of the radiation of the pulsed fiber laser on the surfaces of cylindrical samples made of the VT16 titanium alloy is studied. It is demonstrated that the irradiation at appropriate parameters of the laser radiation in the inert-gas (argon) atmosphere leads to an increase in the microhardness of the surface layer and a decrease in the surface roughness of the irradiated samples by a factor of five in comparison with the roughness of the original samples.