A. K. Shikov

Model of HTS three-phase saturated core fault current limiter

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.

Design of new hollow superconducting NbTi cables for fast cycling synchrotron magnets

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.

Cu-Nb and Cu/stainless steel winding materials for high field pulsed magnets

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.

Study on I/sub c/(T, B) for the NbTi strand intended for ITER PF insert coil

The magnetic field and temperature characteristics I/sub c/(T, B) are important for practical application. This work presents the results of investigations on I/sub c/(T, B) for a strand based on Nb-47.5 wt% Ti alloy. The strand is used in the cable of the ITER PF insert coil, which is under construction. The measurements were carried out in magnetic fields up to 9 T and in the range of temperatures from 4.2 K to 7 K. The critical temperature T/sub c/(B) was determined from voltage-temperature characteristics (VTC) taken in magnetic fields. The temperature dependencies of the upper critical field B/sub c2/(T) were analyzed. By experimental data processing and analysis of literature, relationships describing B/sub c2/(T) and I/sub c/(B, T) dependencies have been defined. Processing programs were used, which allow obtaining all fitting parameters of I/sub c/(T, B) relation.

Status and Achievements in Production of ITER TF Conductors and PF Cables in Russian Cable Institute

Russian Scientific Research and Development Cable Institute (known by Russian abbreviation as VNIIKP) has been participating in ITER project since 1993 both at the early stage of Research and Development (R&D) and at the following stage of Engineering Design Activity (EDA). Tests of several short samples at Sultan test facility were crowned by successful testing of Toroidal Field (TF) and Poloidal Field (PF) insert coils performed in Japan in 2001 and 2008 correspondingly. Now VNIIKP is actively implementing the final production and delivery stage. By 2009 the full technological complex has been accomplished to produce PF cables for both the Russian Federation (RF) and European parts and TF conductors for RF part. In this review we present a short history of VNIIKP participation in ITER and our current achievements. The technology used and our production line are described in some detail.

Development of Cu-Nb alloy microcomposite conductors for high field pulsed magnets

The results of investigation on the influence of the intermediate heat treatment on the mechanical and electrical properties of Cu-Nb alloy microcomposites are presented. The transformation of structure and mechanical properties at the different stages of the production process are discussed. Different designs of microcomposites are developed which allowed to vary the combination of mechanical strength and electroconductivity in sufficiently wide range: UTS - from 900 to 1,200 MPa and conductivity from 65 to 75% LACS. Developed approach to manufacturing process are valid for production of the conductors with enhanced (above 10 mm/spl times/10 mm) cross sections.

Development and research of the Nb/sub 3/Sn superconductor with improved structure of superconductive layer

The creation of a fine uniform grain structure in Nb/sub 3/Sn superconductive layers is one of the methods to increase its current-carrying ability. In this work superconductors with ring filaments were developed, produced and studied. The ring filaments have been distributed uniformly in the bronze matrix to supply more uniform Sn diffusion from the bronze matrix to the filaments. The microstructure of the superconducting layer has been investigated using by SEM and TEM methods, and the critical current dependence on the diffusion heat treatment procedure has been studied. It is shown that Nb/sub 3/Sn layer in such type of filaments has more uniform and fine grain structure without column zone than the ordinary shape of filaments. That leads to an increase for the critical current density of the Nb/sub 3/Sn layer of wire with ring filaments and allows us to reduce the duration of the reaction.

Optimized HTS current leads

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.

Investigation of the multifilamentary (Nb,Ti)/sub 3/Sn conductors with CuNb reinforced stabilizer

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.

Electrical conductivity of high-strength Cu-Nb microcomposites

The conductivity of Cu-Nb microcomposites was studied as a function of the composition and the parameters of the microstructure varying with the degree of deformation. The effect of heat treatment on conductivity of Cu and composites is also considered. The conductivity of Cu-Nb composites with the reduction in area lnA/sub 0//A<4.9 is well described by the Landauer formula allowing for conductivity and the volume fraction of the components. The influence of the principal scattering mechanisms on conductivity of Cu in the composite is treated on the grounds of the experimental results obtained in this work and the analysis of the literary data. The linear correlation between strength and conductivity is obtained for the specimens heat treated at temperatures up to 600/spl deg/C. This correlation is violated, however, for the specimens subjected to heat treatment at temperatures above 600/spl deg/C.