The unique properties of high-temperature superconductors (HTSCs) and progress in the manufacture of HTSC-based wires made it possible to develop a new generation of tokamaks. In Russia, a tokamak project with reactor technologies (TRT), in which the magnetic field induction reaches 8 T on the plasma axis and 15 T and higher on the windings of the electromagnetic system, is being developed. The creation of HTSC current-carrying elements (CCEs) that meet the stringent requirements for the TRT magnetic system is one of the key issues of the entire project. A number of short experimental CCE samples that are potentially applicable in TRT magnetic systems was developed. A series of physical and mechanical tests were carried out to check the mechanical properties and develop a universal certification methodology for CCEs accepted for operation.

The distribution of the trapped magnetic field of untinned and tinned high-temperature superconductors (HTS) tapes after mechanical load on the stack of tapes was studied by the scanning Hall magnetometry method. Based on the obtained data, the values of the average critical current for all the studied samples were calculated. The degradation of the current carry capacity starts with lower mechanical loading on the stack in case of tinned tapes than of untinned ones. For tinned tapes the average value of the critical current drops by more than two times relative to initial state when a mechanical load of 400 MPa was applied; for untinned tapes – a decrease in the critical current is of less than 25%. The obtained data will be useful for further designs of current-carrying part based on stacks of HTS tapes for various applications.

The paper describes a high-temperature superconducting magnetic system (HTS SMS) to equip an experimental stand intended for neuron activity researches under constant and low-frequency magnetic fields up to 1 T. The design of the magnetic system together with its electromagnetic and cryogenic parameters is briefly discussed. The test results of the preliminary experiments conducted in liquid nitrogen at 77 K for two interchangeable magnets are given. The first magnet was manufactured in the form of a double pancake coil wound with 4 mm high HTS tape. The second magnet was made of pure copper wire with no frame and was impregnated with a thermally conducting epoxy resin. The advantages of the HTS pancake coil were demonstrated in comparison with the cryo-resistive solenoid. Low energy consumption of the HTS magnetic system will allow conducting continuous non-invasive monitoring of biological objects in a magnetic field.

Possible macroscopic mechanisms for the destruction of the superconducting properties of a high-temperature YBa 2 Cu 3 O 7 -based superconductor cooled with liquid helium or nitrogen under input of AC are analyzed. It is shown that these mechanisms can be both of thermal and thermoelectrodynamic nature, which is based on the interrelated change in the electromagnetic field induced inside the superconductor and its temperature. Before the emergence of unstable states, intense stable energy dissipation can be observed, which is not taken into account in the current theory of losses. These mechanisms lead to stable supercritical values of the introduced current and the electric field induced inside the superconductor before the onset of instability and, consequently, high permissible overheating. The results discussed expand the scope of practical use of high-temperature superconductors.

This article discusses the issue of selection of material for resistive current leads of superconducting magnets. A wide range of their working modes has been considered. It has been demonstrated that copper is by far not the best material for fabrication of current leads, especially operating at currents exceeding the optimum. In such modes, they are prone to rapid overheating, whereas current leads from alloys can withstand current loads exceeding optimum current by several times. Moreover, in the absence of current, the heat gains from current leads fabricated from alloys are 50% lower than those from copper, which is their obvious advantage. The physical reason for this effect is a strong temperature dependence of copper specific resistance, which leads to positive feedback in the course of increase in temperature of current leads. In addition, the current leads fabricated from alloys have other advantages: significantly higher time of their overheating, as well as wider opportunities for increase in the cooling surface.

The paper describes a high-temperature superconducting magnetic system (HTS SMS) to equip an experimental stand intended for neuron activity researches under constant and low-frequency magnetic fields up to 1 T. The design of the magnetic system together with its electromagnetic and cryogenic parameters is briefly discussed. The test results of the preliminary experiments conducted in liquid nitrogen at 77 K for two interchangeable magnets are given. The first magnet was manufactured in the form of a double pancake coil wound with 4 mm high HTS tape. The second magnet was made of pure copper wire with no frame and was impregnated with a thermally conducting epoxy resin. The advantages of the HTS pancake coil were demonstrated in comparison with the cryo-resistive solenoid. Low energy consumption of the HTS magnetic system will allow conducting continuous non-invasive monitoring of biological objects in a magnetic field.

High-gradient magnetic separator made a good showing at enrichment of low-magnetic ores. However, existing industrial facilities have large dimensions, low specific productivity and high energy costs. Laboratory prototype of high-gradient magnetic separator equipped with superconductor magnet system was developed, manufactured and tested at NRC “Kurchatov Institute”. The device is designed for enrichment of low-magnetic mineral resources, mostly oxidized ferruginous quartzites. The goal of development was both creation of next-generation of separators operating with high-power magnetic fields as well as further progress in applied superconductivity for industrial applications. This paper gives a brief description of the problem, as well as of the process of development, manufacturing and testing the superconducting magnet system. Overall design of the prototype is described, as well as design of collector matrices designed specifically for high-power magnetic field. Next is description of testing process with mineral raw materials obtained from a real industrial enrichment facility. Data on total iron percentage before and after the separation process at the prototype presented, as well as its basic performance characteristics. The results obtained in the course of the project fulfilment can be used in mining industry and metallurgy for manufacturing superconducting magnetic separators of new generation. Such separators will have many advantages comparing with regular separators (with resistive windings) as following: lower energy consumption and less weight, higher induction of the magnetic field in the working gap, possibility to use matrices with coefficient of filling by ferromagnetic precipitating elements at the level of 6-8% with large gaps for pulp passing, higher specific indices due to increased current density in the winding up to 50-100 A/mm2.

The paper gives the results of the experiments with a model two-section REBCO solenoid cooled by either gaseous helium (GHe) or sub-cooled/solid nitrogen (SN2) in (50-77) K temperature range. The major cooling source was a single-stage cryocooler Sumitomo CH-110 with the cooling power of 175 W and 130 W at 77 K and 50 K respectively. The coil itself was not directly conduction cooled. We compare the time taken by both coolants to obtain the temperature of the magnet of about 50 K and the homogeneity of the temperature distribution within the cryostat. Test results for the coil operation in solid nitrogen together with the comparison of its critical properties in SN2 and GHe are also presented.

High gradient magnetic separation is a promising method for ores enrichment and industrial wastes recycling. The potential of separators based on resistive and permanent magnets is limited by the value of magnetic field and operational costs. LTS magnetic systems require liquid helium and complicated cryogenics. HTS magnets operated in solid nitrogen at 50 K can be a possible solution. In this study, we discuss the conceptual design of an HTS rotary separator prototype with the horizontally oriented rotor axis. The scheme allows to organize a continuous ore processing. The split magnet system consists of two 2G HTS coils on a soft-magnetic yoke with 50 mm room temperature gap. The paper gives the overall design of the magnetic system and the related cryogenic, together with the magnetic fields and forces calculations. The preliminary test results of the ReBCO coil in liquid and sub-cooled nitrogen are also presented.

The international project "NICA" (Nuclotron-based Ion Collider fAcility) is an accelerator complex which is under construction at the Joint Institute for Nuclear Research (Dubna, Russia). Basing on the NICA project demands NRC "Kurchatov Institute" (Moscow, Russia) designed and manufactured two trial 12 kA 1G current leads (CLs) intended for powering of the JINR superconducting magnets test bench. The main requirements for the CLs were: a reliable and robust design, usage of liquid nitrogen from the NICA cooling circuits as a resistive section coolant, low resistance joints, current ramp rates up to 10 kA/s and the total heat load to the 5 K end not exceeding 0.4 W/kA per one CL. An in-situ cold test of the trial 12 kA CLs held at JINR in 2015 demonstrated the operational reliability of our technological approaches. Following the successful test results the serial production of 20 pairs of 10.5 kA HTS CLs with very few design updates for the accelerator powering started. The first 10 pairs were fabricated, tested and shipped to JINR as a part of the NICA commissioning framework in June 2017. All the CLs fulfilled the acceptance test requirements. The production of the remaining 10 pairs is to be finished in 2018. The paper gives an overview of the 12 kA and 10.5 kA HTS CLs' design, discusses their thermal, magnetic and electrical characteristics and presents the acceptance tests results. We also compare our CLs with earlier works by other groups in the context of HTS stack-and-soldering technique, joints' resistances, relative heat loads into the cryogenic environment etc.

High gradient magnetic separation is an effective method for ores enrichment and industrial wastes recycling (including radioactive wastes). The possibilities of separators based on resistive and permanent magnets are limited due to relatively low value of magnetic induction and rather high energy consumption. LTS magnetic systems require liquid helium and complicated cryogenics which can be costly and not always optimal for use at industrial facilities. High-temperature superconductors operated in liquid, sub-cooled and solid nitrogen and equipped with cryocoolers are promising materials that can help expanding industrial application of superconducting devices. In this study, we discuss the design of an HTS rotary separator prototype with the horizontally oriented rotor axis together with the magnetic fields and forces calculations that define prototype working parameters; overall design of HTS-2G coils and preliminary test results of the said coils at different operating temperatures.

A high gradient magnetic (HGM) separator prototype with the 2nd generation high temperature superconducting (2G HTS) magnetic system operated in sub-cooled nitrogen is presently under development at NRC "Kurchatov Institute" (Moscow, Russia). The main goal of the project is an attempt to shift away from the complicated liquid helium cryostats towards simple cryocooler-based nitrogen cryogenics as much more convenient for HGM separators industrial applications. Using of commercial HTS tapes allows to get a sufficient level of magnetic fields and extraction forces with low energy consumption. The expected operational parameters of the device are 1.2-1.5 T in the empty operational gap and up to 3 T on the ferromagnetic filters. In this paper we briefly describe the design of the HTS rotary separator prototype with the horizontally oriented rotor axis and propose different types of ferromagnetic filters intended for weakly magnetic ores enrichment.

The feasibility of creating high-current leads on the basis of second-generation (2G) high-temperature superconductors (HTSs) was demonstrated. A method for graded soldering of 2G HTS tape stacks is proposed. It allows one to avoid negative effects that are related to an inhomogeneous current sharing between parallel HTS conductors. A prototype of HTS-coated current leads (CLs) was designed, manufactured, and tested; its critical current exceeds 18 kА. Prototypes of HTS CLs for the superconducting magnetic system of the Nuclotron accelerator (a part of the NICA collider) with an operating current of 6 kA were developed, manufactured, and tested in liquid helium (the overcurrent was 9 kA).