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Processes connected with the diffusion of oxygen in targets for the laser ablation of a superconductive ceramics of composition YBa2Cu3O7 − x have been investigated by the methods of thermal analysis. A two-step mechanism of oxygen diffusion upon isothermal annealings in air has been revealed, which is explained by the incorporation of atmospheric oxygen into different positions, namely, into the interstices and directly into the sites of the crystal lattice.

High strength and high electrical conductivity Cu-Nb tape was tested as the new type of stabilizing layer for YBCO-coated conductor. For electrical interconnection of stabilizing layer to coated conductor the soldering process was used and no degradation in critical current, Ic, of laminated coated conductor after soldering process was observed. The dependence of normalized transport critical current, Ic/Ic0, on the bending radius of coated conductors with and without Cu-Nb stabilizing layer was investigated using the bending test probe providing the uniform bend process at 77 K and under self-field conditions. The reversible and irreversible variations of Ic/I0 with inverse bending radius were found and the irreversible bending radius limit was observed to depend on the neutral axis shift. The generation of the cracks appears to be the primary reason for the Ic/Ic0 degradation that was supported by ScanHall technique investigations.

Epitaxial films of CeO2 and Y2O3 on RABiTS metal tapes have been obtained by pulsed laser deposition. The dependence of the film crystal orientation on the temperature of synthesis has been studied. It is established that Y2O3 films grow with 100% (100) orientation, whereas a parasitic orientation is present in CeO2 films obtained in the entire range of growth temperatures. The texture sharpness in the substrate plane amounted to 8°. Electron-microscopic examination showed that an increase in the temperature of synthesis leads to the appearance of cracks on the surface of CeO2 films, while the surface of Y2O3 films remains continuous in the entire range of growth temperatures. Thus, Y2O3 films most fully obey the requirements to seed layers in (i) being epitaxial with 100% (100) crystal orientation, (ii) inheriting the substrate texture, and (iii) having a smooth crack-free surface.

One of the most effective ways to increase the current-carrying ability of Nb3Sn superconductor is doping of the superconducting phase by Ti, since it leads to Hc2 increase due to the rise of Nb3Sn phase electrical conductivity in normal state, and also to acceleration of the Nb3Sn layer growing during reaction and to critical current density increasing. The investigations of structure and composition of Nb3+xSn superconducting strands by SEM, TEM and EDXS microanalysis have been carried out. The structure and composition of Nb3Sn superconducting phase of the strands after reaction at 575°C 150 h+650°C 200 h have been studied. The dependence of Ti content in Nb3Sn phase from the amount of Ti introduced in Nb filaments or in bronze matrix has been also studied. It was found, that the lowest Ti content corresponds to introduction of it through the matrix doping. It has been established that Nb content in Nb3Sn essentially exceeds the stoichiometric one (3:1). The Nb3Sn lattice parameters have been defined by XRD. It was found, that the lattice parameters in the samples with Ti doped matrix were the closest to the stoichiometric Nb3Sn. The correspondence between grain morphology and composition of superconducting phase and critical current density of studied strands has been established.

Several years ago at Kurchatov Institute the R&D program on the new type of superconducting magnets (SM) doped with large heat capacity substances (LHCS) in order to improve their stability was started. We began from an “external” doping by the LHCS powder mixed with epoxy resin using the wet-winding process. Later on at Bochvar Institute the methods to introduce LHCS inside superconducting wires (both NbTi and Nb 3 Sn based) were developed. The comparative tests of LHCS doped wires and model windings with LHCS have shown positive results regarding a considerable increase of critical energies, improving of thermomagnetic stability and training behavior. The state-of-the-art of these methods is reviewed and their perspectives are discussed.

The results of investigations of first 500 kg Nb3Sn bronze strand are presented. This batch of strands was meant for the production of 100 m of Toroidal Field Conductor in the frame of fulfillment the Phase II of Procurement Arrangement between Russian Domestic Agency and International Organization ITER. In order to provide the industrial-scale production of strands design documentation and all necessary quality assurance documents were developed. The developed industrial technology of Nb3Sn strand production was applied in Joint Stock Company "Chepetsky Mechanical Plant" (JSC "ChMP"). Strands were produced in JSC "ChMP" from final billets with diameter of 203 mm. The microstructure investigations of produced strands were performed before and after diffusion annealing by optical microscopy, X-ray microprobe analysis. Mechanical properties of annealed Nb3Sn strands were investigated. Current-carrying capability of Nb3Sn strands at 12 T, 4.22 K were studied. It was shown, that all produced strands met all the requirements, in particular Ic was from 202 to 220 A; hysteresis losses were from 165 to 194 mJ/cm3 (± 3 T ).

The effect of radiative heating of the surface of an HTS target on its oxygen index during the growth of HTS coatings by pulsed laser deposition is studied. It is shown that, during growth, the oxygen index of the HTS target varies in a range of 6.85–6.12. It is revealed that the oxygen index of HTS coatings formed by pulsed laser deposition does not depend on the oxygen index of the sputtering target at an identical cationic composition.

The nanostructured microcomposites with FCC (Face Centered Cubic lattice) copper metal matrix and BCC (Body Centered Cubic lattice) metal strengthening filaments uniformly distributed in copper matrix are characterized by specific unique combination of physical and mechanical properties that distinctly differs from the properties of coarse grained macrocomposite materials. The experimental investigation on the influence of the nature of BCC strengthening elements is presented. Cu-Nb, Cu-V and Cu-Fe microcomposite wires have been designed and produced with the use of the same fabrication approach. The main mechanisms of microstructure transformation for all three composite materials have been analyzed. The possibility to attain the optimum microstructure with extremely high volume fraction of internal phase boundaries for each of the investigated microcomposites has been estimated. The data on the mechanical strength and electrical conductivity of Cu-Nb, Cu-V and Cu-Fe microcomposites are presented. The correlations the attained mechanical strength and conductivity with microstructure parameters are analyzed.

Multifilamentary Nb3Sn-based superconducting composites manufactured by an internal-tin method have been studied by transmission (TEM) and scanning (SEM) electron microscopy. The main goal of this study is to reveal the effect of diffusion annealing regimes as well as the external diameter of the wires on the structure of nanocrystalline Nb3Sn layers (average grain size, grain size distribution, layer thickness, amount of Sn, etc.). It is demonstrated that multistep diffusion annealing results in quite a complete transformation of Nb filaments into Nb3Sn though some amount of the residual Nb remains in the filaments center. With an external diameter decrease the superconducting layers structure has been found to refine and get somewhat more uniform. An additional high-temperature annealing results in marked growth of Nb3Sn grain sizes and their scattering in sizes, which may negatively affect the current-carrying capacity of a wire.

In the USSR and later in Russia, the main activities in technical superconductivity were concentrated in the institutes that belonged to the Ministry of Atomic Energy (Minatom). The development of new technologies shortly transferred to the large-scale industrial production of NbTi and Nb 3 Sn superconductors in early 1970s. Two main technologies for multifilamentary Nb 3 Sn strands were under investigation during that time – bronze-process and internal tin method. More than 25 ton of Nb 3 Sn bronze-processed strands were produced for the fabrication of 90 ton of conductors for application in the magnet system of first in the world fusion facility (tokamak T-15) with magnet system based on the intermetallic compound. The characteristics of these strands and conductors have been briefly described. The requirements for the Nb 3 Sn strands constantly increased and the main R&D on the enhancement of critical current density have been reviewed. For bronze-processed strands the increase of the tin content in large ingots was the crucial factor. The artificial doping of niobium filaments by niobium–titanium alloy was invented, which enabled to improve the workability of Nb 3 Sn strands, with enhanced critical current density in high fields. For internal tin Nb 3 Sn strands the main R&D were concentrated on the optimization of the layouts of the strand and on the multistage heat treatment because of the inevitable liquid phase formation which could result in severe distortion of the geometrical arrangement of the filaments and even in destruction of the whole strand. The main results of these investigations have been presented. The corresponding impact of these R&D on the design of bronze-processed and internal tin strands has been analyzed. The quantitative estimations of the grain size were made for bronze-processed and internal tin strands. It was shown that in bronze-processed and internal tin strands subjected to the standard ITER heat treatment characterized by two stages at 575 °C and 650 °C, the variation of Nb 3 Sn grain size in the range of 30–300 nm could be observed. The correlations of microstructure and superconducting properties have been discussed. The ITER connected activities in Russia on the development of Nb 3 Sn strands, which met the HP-II specification, have been outlined. The results of the ITER Model Coil Program have shown a degradation of the critical current of large cable-in-conduit conductors (CICC) built with Nb 3 Sn strands. For this reason, the investigation on the strain dependence of critical current density in Nb 3 Sn strands of different designs is of high interest and priority. The R&D on development of bronze-processed and internal tin Nb 3 Sn strands with enhanced, by the nanostructured Cu–Nb material, mechanical strength have been reviewed.

The study of superferric synchrotron magnets with a pulse repetition rate up to 20 Hz is performed at the Laboratory of High Energies of the JINR during the last years. The magnet feature is a low inductance superconducting coil made of a high current hollow cable, cooled with two-phase helium flow at 4.5 K. After the successful tests of fast-cycling 1.4 m model dipoles at the field ramp up to 7 T/s, a proper quadrupole is under design and construction. The new magnet yoke length is about 420 mm and the distance between the pole shoes is 90 mm. The cable comprises 24 wires of 0.73 mm diameter are wound around a copper-nickel tube with an outer diameter of 5 mm. The wire consists of 10374 NbTi filaments of 4.2 mum diameter. It is expected that the new 32 T/m quadrupole magnet will operate at pulse repetition rate up to 10 Hz providing the field gradient ramp of 600 T/m per second. The first tests have been carried out in August 2006. Status of the work and obtained results are presented and discussed.

Based on the results of X-ray diffraction analysis of texture of the Zr-1% Nb and Zr-2.5% Nb model alloys compressed uniaxially at temperature corresponding to the β and α + β fields of the phase diagram, the mechanisms responsible for plastic deformation have been determined. These are the crystallographic slip in the β-Zr and α-Zr grains and also the diffusional mechanism of mutual displacement of crystallites along interphase boundaries, which is activated upon the α ↔ β phase transformations and is the basis of superplasticity. The contribution of each mechanism to the formation of specimen texture depends on the temperature-rate regime of compression.

The data from the investigation of hollow superconducting cable based on keystoned NbTi wires are presented. The cable sample, consisting of 15 wires wound around a cooper-nickel tube 5 mm in diameter and cooled with two-phase helium flow has operated inside the magnet aperture at a current of 13.4 kA and the current ramp rate of 26.8 kA/s. The external magnetic field value was about 2 T and the field ramp rate of 4 T/s. The pulse repetition rate of 1 Hz was provided. The first 650 m of the new wire was manufactured based on the improved technology. A piece of hollow cable 40 m in length was fabricated. The outer cable diameter with electric insulation is 7.34 mm. A test winding for a 1.4 m superferric nucleotron-type window frame model dipole for SIS100 as part of the FAIR-project of GSI was fabricated and tested. The obtained results are discussed. The new approach to a 'cable-in-conduit' conductor cable design, based on the use of keystoned wires, is described.

Results of a study of promising Nb3Sn superconductors fabricated with the use of a “bronze” method and a method of “internal source of tin” for toroidal coils of the magnet system of the international thermonuclear experimental reactor (ITER) are presented. The main structural parameters and factors of the process of manufacturing technical superconductors based on Nb3Sn, which determine the superconducting properties, are analyzed. The current-carrying capacity and the losses to hysteresis are determined for conductors with various diameters. The structure of the layer of superconducting Nb3Sn compound is studied, and the relation between the structural parameters and the superconducting properties of the developed conductors is described. Examples of Nb3Sn superconductors with a reinforcing element from a nanocomposite alloy Cu - 18% Nb are presented. Strength characteristics of the reinforced conductors are studied. Prospects of further enhancement of superconducting properties of Nb3Sn superconductors obtained by both methods are estimated.

The peculiar feature of Nb 3 Sn diffusion grown layers is the presence of intrinsic regions, which differ by the composition and microstructure. These regions can be treated as Nb 3 Sn macrononhomogeneity. Internal stresses and composition fluctuations in Nb 3 Sn grains can be associated with the micrononhomogeneity. Both types of the inhomogeneites exhibit itself in the shape of superconducting transition characteristics. In the present work voltage–current and voltage–temperature curves were studied for Nb 3 Sn model flat conductor and ITER type multifilamentary strands.

Two new options for a hollow NbTi superconducting cable were considered. The first one is based on keystoned wires wrapped around a copper-nickel tube 5 mm in diameter. The second one is a hollow cable of rectangular cross section. The data from cable short sample tests are presented. Some problems with the production technology are discussed. This work is part of the R&D for the Future Accelerator Facility, at GSI in Darmstadt.

According to requirements of the applications (fusion reactors, accelerators or superconducting switches), different NbTi and Nb 3 Sn strands have been developed and manufactured at Bochvar Institute (VNIINM) for several last years. Design of the fusion and accelerator strands is dependent on the required performance and function of the conductor to be used. Good performance superconducting persistent switches called for the use of high electrical resistivity matrix together with high current properties. The characteristics of the strands manufactured for toroidal (Nb 3 Sn) and poloidal (NbTi) field coils of experimental fusion reactor ITER are presented as well as the accelerator strands based on NbTiTa alloys and Nb 3 Sn and also the wires with CuNi and CuMn matrices for superconducting persistent current switches.

The causes of hydrogen charging of zirconium parts in cores of VVER and RBMK reactors during manufacturing and operation and the factors influencing these processes are considered. The laws governing the influence of hydrogen charging on the fracture toughness of thin-wall zirconium parts are studied. It is shown that cracks may develop in thin-wall zirconium parts of fuel rod arrays under the action of hydrogen by the mechanism of delayed hydride cracking. The effect of irradiation on the rate of crack propagation in zirconium parts due to delayed hydride cracking is considered.

The expedience in the use of hafnium for control elements of a nuclear reactor is considered. The requirements of various producers on the chemical composition and mechanical properties of nuclear-purity hafnium are presented. Results of studies of the strain resistance and ductility characteristics of hafnium are discussed depending on the temperature and the deformation rate. The dependence of the hafnium hardness on the degree of deformation and on the annealing mode is presented. Results of a texture analysis are used to judge the effect of deformation and heat treatment on the anisotropy in the properties of hafnium. The developed process is used for the production of hafnium parts at VNIINM, i.e. hafnium plates are fabricated for the attachment unit of automatic control assemblies (ACA) for VVER-440 reactors.

New type of superconducting material is presented in form of thin composite mono- and multilayers (multifilamentary) sheets based on Bi-2223 compound in metal matrix. Such sheets with 0.2–1.0 mm in thickness, up to 300 mm in width and up to 10 m in length contain up to 20 thin superconducting layers (or filaments). Different testing methods are applied in order to estimate the superconducting properties of the sheets namely critical current measurements, so called “field mapping” and levitation tests as well. It has been established that the field dependence of critical current for sheet Bi-2223/Ag material is the same as the one for usual Bi-2223/Ag long length multifilamentary tapes. Possible applications of sheet-like Bi-2223 based material are discussed and some results are presented for cryomotors, coils and current lead elements created with using of such HTSC materials.

Phenomena of silver penetration into ceramics of single-filament and multifilamentary (61 filament) Bi1.6Pb0.4Sr2Ca2Cu3Ox/Ag composite ribbons have been investigated by means of transmission electron microscopy (TEM), X-ray microanalysis, X-ray photoelectron spectroscopy and high-resolution Auger spectroscopy. Distribution curves of Ag in the ceramics have been plotted from the Ag-sheath farther inside the ceramics. A nonuniform distribution of Ag was revealed by high-resolution Auger spectroscopy in ceramics far from the Ag-sheath, which is in agreement with TEM results. Ag is found in the ceramics in form of isolated particles located along plane boundaries of crystallites (grains). Near the Ag-sheath there is a lot of particles, and in moving farther away from it their density decreases remarkably. Two mechanisms of Ag penetration into ceramics have been discovered: (a) conventional diffusion, shown by some other authors as well; (b) indentation of ductile Ag into brittle and porous ceramics in the process of plastic deformation of a composite. Ag-sheath strengthening caused by alloying with (Ni+Y) and (Zr+Al) drastically decreases the effect of the second mechanism. The previously described for unalloyed composites phenomenon of critical current instability with respect to thermal cycling in the temperature range of 77–293 K [1] has been understood and explained. It results from thermal stresses caused by the difference in coefficients of thermal expansion of Ag and the ceramics. These stresses arise not only at the Ag/ceramics interface, but also within the ceramics layer of about 10 μm thick. This can result in a fault of contact between grains. Ag-sheath strengthened by alloying drastically decreases the amount of silver in the ceramics and eliminates the composite instability.

Monofilamentary Nb 3 Sn wires of large diameter with niobium tube, which were obtained by the method of solid-phase diffusion, are well suited for the study of the distribution of the critical temperature T c in Nb 3 Sn layers. Three regions with different gradients of Sn and Nb concentration and different Cu content can be distinguished in Nb 3 Sn layer. In the central part of the layer, the Sn content comprises 24.5 at.% and the gradient of Sn concentration is negligibly small. Measurements on specimens of 1.2 mm in diameter with a slit cut along the cylinder generatrix showed that the critical temperature of the Nb 3 Sn region adjacent to Cu(Sn) bronze is lower than the critical temperature of the central part of the layer. Fluctuations of T c in the central part of the layer exceed the change of T c related to the gradient of the Sn concentration, which is very small. These fluctuations spread both the R ( T ) curve and the high-temperature part of the temperature transition registered by the inductive method.

Test of HTS dipole with coil wound by Bi-2223 tape was carried out. Volt-current characteristics of the dipole at various temperatures as well as results of magnetic field measurements are presented. A process of transition to normal state for the HTS coil was calculated.

Resistivity of the high strength CuNb microcomposites have been investigated just in the process of tensile testing at the temperatures of 293 K and 77 K. Two processes determine the character resistivity-strain dependencies in microcomposites during elongation: the increase of the lattice defects concentration in copper which leads to the increase of resistivity; the decrease of compression of Cu lattice along the conductor axis which leads to decrease of resistivity. It was shown that the deformation of microcomposite wires at 77 K with following relaxation at 293 K led to the increase of ultimate tensile strength at room temperature. This increase could be as large as 3-6% depending on the level of strain applied at cryogenic temperature.

Last year Bochvar Institute (VNIINM) has developed and produced several NbTi strands of various layouts intended for the cables of ITER PF coils. Strand layouts distinguish by filament diameter, Cu/non-Cu ratio and Cu matrix distribution between the center and periphery of cross-section. Among them two strands contain an internal CuNi resistive barrier. The studies on critical current properties at 4.5-8 T are performed and also on electrodynamics behavior of the strands, including AC losses at varying magnetic fields up to 3 T and frequency up to 10 Hz. The experimental results are presented on hysteresis losses and time constant.

The superconducting cable-in-conduit conductor (CICC) for the TF Coil Insert (TFCI) consists of the cable (1152 superconducting Nb/sub 3/Sn strands of 0.81 mm diameter) jacketed by welded titanium conduit. All superconducting strands are covered by Cr layer of near 2.5 /spl mu/m thickness and cabled in five stages. The sub-cables and the full cable are wrapped by the thin SS tape. The manufacturing procedure was carried out for a jacketing of cable by the tubes of titanium (2.0 mm thickness). This paper presents the description of the conductor manufacturing process. cabling, welding of conduit, insertion of cable, compaction, winding of coil and QA procedure. The coil of TFCI was made of the superconducting conductor successfully.

The connection between microstructure and electrical transport properties of 99.99% purity copper for Cu-stabilization of superconductors has been investigated. Microstructure of copper was studied by optical and transmission electron microscopy. The chemical composition analysis of impurities has been carried out on base of the laser mass-spectrometry data. The electrical transport properties have been estimated by residual resistance ratio (RRR). It is shown that the difference in RRR values obtained for the studied samples are connected to the microstructure features, mainly with the surface of grain boundaries and concentration of second phases precipitation. The experimental correlation of RRR and concentration of precipitation (0.01–0.08 vol%) and oxygen content (0.001–0.003 wt.%) have been obtained. The influence of the conduction electron scattering by the different mechanisms on the electrical conductivity has been discussed. The comparison of measured RRR values and theoretically estimated ones was carried out.

The features of corresponding manufacturing process for Cu–Nb microcomposite wires are presented. Investigation on the influence of the microstructure and crystallographic parameters on strength and conductivity properties of model microcomposite wires and conductors with cross-sections up to 26 mm 2 are presented. The estimation of the potentially achievable mechanical and electrophysical properties of Cu–Nb microcomposite wires has been done. For Cu–Nb wires with 11 mm 2 cross-section the RT ultimate strength 1350 MPa, the RT yield strength 1200 MPa, RRR exceeding 4.6 and conductivity near 65% IACS have been attained.

The results of the study of the temperature-transition profile in magnetic fields and of the critical current J c ( T , B ) in multifilamentary Nb 3 Sn conductors of different design are considered. We also analyze the contribution of the components with different critical parameters to the current-carrying capacity at high magnetic fields, and the possible causes of inhomogeneity of multifilamentary Nb 3 Sn conductors of different design formed by “bronze” technology and by “internal tin technique”.

Bochvar Institute (VNIINM) has developed and produced fine filament NbTi superconducting strands of several layouts for International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) coils. The strands, having outer diameter of 0.7 mm and filament diameter of 6.5 μm, have been manufactured both by single and double stacking. Strand layouts distinguish by Cu/Sc ratio and a filament zone arrangement in cross-sections, one of them includes CuNi resistive barriers to reduce AC losses in operating condition of ITER magnet system. The results of comparative investigations on critical currents, critical current density, AC losses, critical temperature of the strands are presented. Two strands of these layouts are supposed to be used in the experimental cable for the model coil of SULTAN facility.

Two promising types of Cu/SS macrocomposite and Cu–Nb microcomposite winding wires for large-scaled high-field pulsed magnets are reviewed. The features of corresponding manufacturing processes for Cu/SS and Cu–Nb wires are presented. It was shown that the manufacturing process designed for the fabrication of composite multifilamentary low-temperature superconducting wires could be successfully applied for the production of high strength, high conductivity Cu–Nb microcomposite conductors. The strength–conductivity properties of several types of Cu–Nb and Cu/SS conductors are given. The microstructure of Cu–Nb microcomposite conductors has been investigated by means of SEM and X-ray analysis. The influence of microstructural parameters on the mechanical and electrical properties has been analyzed. The room temperature (RT) ultimate tensile strength (UTS) at the level of 900–1100 MPa and conductivity 50–60% IACS for Cu/SS conductors with cross-sections up to 40 mm2 have been attained. The strength–conductivity properties of several types of Cu–Nb microcomposite wires with continuous and “in situ” formed discrete filaments are presented. For Cu–Nb “in situ” wires with 6 mm2 cross section the RT UTS exceeding 1400 MPa and conductivity ∼60% IACS have been attained.

A survey is given of the Russian superconducting materials for the magnet systems of fusion reactors such as `Tokamak-7', `Tokamak-15' and ITER. In total, approximately 10 t of superconductors based on Nb–Ti for Tokamak-7 and 26 t of superconductors based on Nb 3 Sn (25 t for Tokamak-15 and 1 t for ITER) have been produced. Also reported here are test results of strands produced for the coil-insert conductor for the central solenoid of magnet coils for ITER. The results show small variation in values of critical current, hysteresis losses, residual resistance ratio, and others, which meet the ITER high performance specifications (HP-II). The possibilities of improving critical characteristics by optimization of strand design produced by the bronze and internal-tin process and by processing composite superconductors based on HTSC-compounds have been also considered.

Laser targets made of beryllium deuteride BeD2, nanocrystalline beryllium and of low-density beryllium are reported. Spherical laser targets are strong enough and are capable of storing DT-mixture ...

Two promising types of Cu/stainless steel (SS) macrocomposite and Cu-Nb microcomposite winding wires for large scaled high field pulsed magnets are reviewed. The estimation of the potentially achievable combinations of mechanical and electrophysical properties has been done. The features of corresponding manufacturing processes for Cu/SS and Cu-Nb wires are presented. The strength-conductivity properties of several types of Cu-Nb and Cu/SS conductors are given. Relationships between the microstructure parameters and mechanical properties of Cu-Nb wires are discussed. The RT (room temperature) ultimate tensile strength at the level of 900-1100 MPa and conductivity 50-60% IACS for Cu/SS conductors with cross-sections up to 40 mm/sup 2/ has been attained. For Cu-Nb wires with 6 mm/sup 2/ cross section the RT ultimate strength exceeding 1400 MPa has been attained.

In frame of Se.C.R.E.T.S. international task Nb/sub 3/Sn strands with 50 and 60% of Cu fraction have been produced and comparative research of their performance (Q, I/sub c/, J/sub c/, RRR, etc.) have been carried out. Strand design and processing were identical. However, the decrease of Cu fraction value has influenced on RRR value as well as Cr-plated and bare strands. By method of subsequent approximation the estimation of diffusion coefficients of Cr into Cu by R275/R20 values of both strands have been carried out. These calculations have shown that Nb/sub 3/Sn strand after reaction at the standard regime (575/spl deg/C 150 h+650/spl deg/C 200 h at 10/sup -5/ Torr) characterized the value of diffusion coefficient /spl sim/10/sup -12/ cm/sup 2//s, that has led to Cr penetration into oxygen free Cu in not more than 40 /spl mu/m of depth. The calculations of RRR integral value versus reaction time and Cu thickness have also been done. The relation of diffusion coefficient and microstructure of Cu-stabilization has been discussed.

Comparative investigations of superconducting properties at 4.2 and 2 Kelvin are presented for NbTi and NbTiTa wires manufactured by identical heat treatments. Three NbTiTa alloys with 12.4; 14.0 and 20.4 wt% Ta have been studied in this work. Single and double stacked wires with filament diameter from 20 to 3 /spl mu/m are under the consideration. An attempt to optimize critical current density for high field application is described.

A small (several hundred watts) model of a three phase saturated core HTS fault current limiter (FCL) was developed and tested. Iron yokes of all three phases were saturated by a single DC HTS coil. The coil comprised a 60 turns single pancake (ID 135 mm), wound after heat treatment from Bi-2223 multifilamentary tape in Ag matrix. The critical current of the pancake in liquid nitrogen was 8 A. The tests have shown that the limiting value of the AC current (at 50 Hz) can be easily adjusted in the range from 8 A to 20 A depending on the value of the DC current in the HTS coil. The optimum value of the latter is 4 A, corresponding to the 8 times increase of the differential resistance in the current limiting mode. The response time is very short (less that 1 ms). Under tests the short-circuiting event was made in one, two and all three phases. The case of short-circuiting of one phase in the three-phase FCL is especially favorable from the standpoint of the voltages induced in HTS coil compared to the one-phase FCL.

A 600 A High Temperature Superconductor (HTS) current lead has been designed, fabricated and tested. The design of the HTS current lead is optimized to reduce the heat leak and to operate safely during fault mode conditions. The current lead consists of a resistive part cooled with helium forced flow and HTS part that is cooled with boiled off helium gas. The HTS part is composed of Bi-2223 with Ag 10 at.% Au alloy matrix. Results of the electrical and thermal tests of the current lead are presented.

Achievements in the technology of superconducting magnets for the tokamak fusion devices contribute to the applicability of GJ-range SMES for the utilities by means of using already developed components and constructed production lines. The paper presents the technologies developed by the NIIEFA, VNIIKP and VNIINM, institutes, covering most of the critical items needed to construct the GJ-range SMES devices for the utility needs. That includes software packages for the supporting analysis and SMES optimization, heavy current CICC production lines with the length of pull-through jacketing tooling of up to 1 km, 30 kV 40 kA-range cryogenic current leads and 30 kV high-pressure insulating breaks for "cold" and "warm" helium communications, various types of heavy-current 30 kV range commutating equipment, including superconducting switches, and cryogenic test facilities for the acceptance tests of the produced conductors, current leads and insulation breaks.

Comparative study was carried out on characteristics of model NbTi superconducting strands and (6+1) cables with copper-nickel (up to 29 wt.% nickel) and copper-manganese (up to 13.5 wt.% manganese) matrices. Hysteresis losses per cycle are presented for 0.2 mm strands at field amplitude from /spl plusmn/0.5 up to /spl plusmn/3 T. The contribution of own hysteresis of magnetization of copper-manganese matrix into integrated losses appreciably increases at fields above 1 T, while at fields below 1 T losses are comparable for both copper-nickel and copper-manganese strands. Losses at frequency up to 45 Hz and field amplitude up to 1 T for the CuMn cable without transport current are identical to those at slowly varying field. Rate dependencies of critical current in the cables are presented at linear build up of transport current. Critical currents in the CuMn cable at linear current building up and sweep rate exceeding that required for commercial frequency are not less than DC (/spl ges/260 A at 1 T).

Materials and manufacturing aspects are considered concerning high current HTc-superconductors such as BiPbSrCaCuO-based composites and bulk YBCO ceramics as well. Complex influences of chemical and phase compositions as well as different manufacturing parameters are shown on the current carrying capability of such conductors. Some questions connected with doping problems in HTc-materials are discussed and uranium-doping among them. New HTSC materials in form of composite sheet-like superconductors are presented. Some examples of application for HTSC materials such as long length BiPbSrCaCuO tapes and sheets, large grain bulk YBCO are presented namely current leads, current limiters and HTc-rotors of cryogenic motors as well.

Two Nb/sub 3/Sn cable-in-conduit conductors have been procured for Se.C.R.E.T.S. (Segregated Copper Ratio Experiment on Transient Stability). The two conductors are identical in the fractional cross sections. The only difference is the location of the copper stabilizer, included either as segregated copper wires or as copper shell in the superconducting strands. A number of characterization tests, on individual strands and cabled conductors, have been carried out to establish a solid data base for the assessment of the results in the main experiment.

Heavily cold drawn in situ Cu–Nb composites have been investigated by transmission electron microscopy (TEM) and X-ray analysis. Dislocation density in the copper matrix has been shown to change only slightly in the investigated drawing ratio range because of the development of stage IV of deformation. In Nb filaments dislocation density in the investigated range at first increases with deformation and then drops at the highest drawing ratio. At intermediate deformation niobium grains consist of fine blocks separated by low-angle dislocation boundaries. At drawing, fibre texture develops in both phases, with 〈111〉 and 〈100〉 axis for the copper matrix and 〈110〉 axis for niobium filaments. Besides, niobium filaments acquire ribbon-like form, and their grains possess certain orientation, namely, in interlacing grains crystallographic {311}, {100} and {111} planes are parallel to each other and to the filament plane, i.e., the rolling texture with {311}〈110〉, {100}〈110〉 and {111}(110) components is forming within every filament.

In Se.C.R.E.T.S. (Segregated Copper Ratio Transient Stability), the stability performance under transverse field transient is compared for two Nb/sub 3/Sn cable-in-conduit conductors which differ only because of the different distribution of the stabilizing copper, either included in the Nb/sub 3/Sn strand cross section or segregated as bundled copper wires. If the segregated copper is found to be effective for stability purposes, the copper fraction in the Nb/sub 3/Sn strands can be substantially reduced, with dramatic cost advantage for the high field fusion magnets. The experiment is assembled in the SULTAN facility at CRPP, with 11 T background field and superimposed transverse pulsed field to generate the transient disturbance. The layout of the conductor, the winding sample and the assembly procedure are described. The instrumentation and the test program are planned to provide results to be easily extrapolated to the ITER conductors.

The problem of optimizing HTS current leads by varying their cross-section along the length is investigated both experimentally and numerically at 500 A current level. Bi-2223-based HTS multi-filament composite tapes were used with two types of matrices: pure Ag and (Ag+1 at.% Au) alloy. The warm ends of the HTS parts of the current leads were cooled with liquid nitrogen. Very low evaporation rates in the case of Au-doped matrix and rather long time constants to reach thermal equilibrium were observed.

Some results of AC loss measurements are presented for 19, 61, 127-filamentary Bi-2223/Ag tapes prepared by the `powder-in-tube' method. All measurements have been made at T =77 K under sinusoidal transport current with frequency in the range of 30–600 Hz and the current amplitude up to 30 A. The measurements have been carried out both in self field conditions and at the external magnetic field applied to the tape at the different angles. The dependencies of the AC losses on current amplitude and frequency have been obtained. It is found that for all tapes the current amplitude dependencies of the AC losses show good agreement with the Norris prediction for an elliptical or strip geometry. The AC loss dependencies on frequency were linear. The measurements of AC losses in external magnetic field show that the change of AC losses is only through the change of the critical current. So the transport AC losses in the tapes are the `saturation losses' that is they are different from classic hysteresis losses.

A review is given of the present status of the development and production of Nb3Sn and Nb–Ti superconductors for the Model Coils and the real Magnet System of the International Thermonuclear Experimental Reactor (ITER) in the Russian Federation Home Team. It is shown that Nb3Sn bronze processed superconductors produced for the Model Central Solenoid Coil insert meet the ITER joint Central Team requirements. In particular, the critical current density, measued in non-Cu area is not less than 550 A/mm2 for 12 T at 4.2 K, the level of hysteresis losses is not in excess of 200 mJ/cm3, and the Cu-stabilizing shell resistivity ratio of Cr-plated wire is 150. Internal tin Nb3Sn superconductor development and test results are presented, confirming the possibility of their application for the ITER Magnet System winding. Nb–Ti superconductors for PF coils properties have also been considered. The possibility of Nb3Sn and Nb–Ti superconductor manufacture with the use of large composite billets up to 300 mm in dia is shown, creating the possibility for large scale industrial production (several tens of tons/year) of these materials for the ITER Magnet System.

The effect of bending strain on Voltage-Current Characteristics (VCC) of BiPbSrCaCuO-2223/(Ag and Ag-alloy sheathed) tapes with and without Ag additions into the core have been studied. The testing probe allows us to carry out all set of bending tests up to radius 5 mm on the same specimen. The critical current Ic and shape of high-sensitivity VCC as a function of bending strain are analysed. Degradation of current carrying capacity under bending deformation is caused by the formation of microcracks. The overlapping of microcracks in Bi-2223/Ag sheathed tapes without Ag additions leads to current overflow into the Ag sheath and to appearance of linear resistance segment in the V-I curve at low electric field.

Multifilamentary Nb/sub 3/Sn superconducting wires with Cu stabilizer reinforced by Cu-16% Nb circular layer and with the filaments artificially doped by Ti were developed. Microstructure, mechanical properties, superconducting parameters of (Nb,Ti)/sub 3/Sn wires with round and rectangular cross sections were investigated. The influence of heat treatment regimes on the wires critical current density in magnetic fields up to 14 T was examined. The changes of critical current density under the axial strain at 4.2 K were analyzed and distinct shift for a higher strains without diminishing of the critical current was confirmed. The comparison of obtained results with the appropriate values for the similar wires without Cu-Nb reinforcement was made. It was shown that the ultimate tensile strength and yield strength for the developed wires were higher in a factor of 1.5.