S.I. Novikov

Experimental observation of space magnetic anisotropy

Abstract It has been experimentally discovered that there exist certain regions in strong magnetic fields of solenoids where the substance is subjected to a force which is different from the magnetic one. The angular arrangement of this region in the solenoid aperture depends on the time of day and the season. This indicates space magnetic anisotropy.

Computations of voltage-current characteristics for a stabilized inhomogeneous superconductor with thermal resistance across the boundary between the superconducting wire and the substrate

Abstract A quench in modern multifilament conductors with voltage-current characteristics, broadened due to a longitudinal inhomogeneity of a critical current, occurs at electric fields high enough to be easily registered. It provides an opportunity to control superconducting solenoids made of such conductors, even in the case when steady-state stabilization is absent. Use of a semiempirical relationship for voltage-current characteristics of multifilament wires permits the computation of the main characteristics of a combined conductor consisting of such wires and of a stabilizing substrate. Presence of a thermal resistance across the boundary between the wire and the substrate decreases the quench current insignificantly, but causes a considerable drop in the electric field at which the quench occurs.

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.

Results of the model coil tests for the cable-in-conduit conductor for SST-1 tokamak

SST-1 tokamak, under fabrication at Institute for Plasma Research (IPR), India, deploys superconducting coils for both toroidal field (TF) and poloidal field (PF) magnets. A NbTi based 135 strands cable-in-conduit conductor (CICC) has been fabricated for this purpose by M/S Hitachi Cable Ltd. (Japan) under specification and supervision of IPR. In order to test the performance of this CICC under SST-1 operating scenarios, a Model Coil (MC) has been designed, fabricated and tested at Kurchatov Institute (KI), Russia using the SST-1 CICC under a collaborative program between IPR and KI. The MC was designed to have the same maximum field-to-current ratio (5 T at 10 kA) as of the SST-1 TF coils. Typical SST-1 disturbances were simulated with a toroidal array of four longitudinal disturbances simulating coils and with two transverse disturbances simulating coils.

The study of structure and properties of Nb/sub 3/Sn layers in multifilamentary superconductors manufactured by the internal tin method

The processes of diffusion interaction of niobium filaments and a copper matrix in conductors manufactured by the internal tin method were investigated. The aim was to determine the effect of heat treatment modes on the structure and properties of a Nb/sub 3/Sn layer being formed in conductors with the centrally positioned Sn alloy. It was established that as a result of the doping of the matrix and filament materials, the overall critical current density (without taking into account the stabilizing copper) reaches into 5.12*10/sup 4/ A/cm/sup 2/ in a 16-T field and 2.08*10/sup 4/ A/cm/sup 2/ in a 18-T field.

Superconducting magnet for high speed ground transportation

This paper presents the design of a superconducting magnet intended to propel, levitate and guide a magnetically levitated vehicle by means of combined ground propelling circuits. It also describes the on-board cryostat with an indirect immersion cooling system which enables both longitudinal sides of the vertical superconducting magnet to create an electrodynamic force. During coil testing a magnetomotive force of 450 kA was achieved with the maximum induction of 3.5 T at the winding surface.

Superconducting conductor for T-15 toroidal magnet

Design parameters and material and performance requirements are presented and evaluated for the superconducting toroidal field magnet for the next-generation T-15 tokamak reactor. The superconductor currently under consideration is a composition of an eleven-strand transposed niobium-tin conductor and two copper tubes, combined by a layer of electrolytic copper. The superconducting properties of the niobium-tin bronze matrix composites were analyzed, including critical current density, stability under plasma current flow disruption, critical temperature and field, dependence of the critical parameters on strain, reaction of the current-carrying element to a longitudinal pulsed field, and the smeared nature of the transient characteristic. Testing scenarios are described. Superconducting values were also calculated.

Scaling of the

Voltage- current characteristics VCC(epsiv, B, 4.2 K) have been measured in the range of the applied axial tensile strain (epsiv) from 0% to 0.93% at magnetic fields 10 T and 12 T for ITER type bronze processed Nb3Sn strand and for similar strand with enhanced mechanical strength in which part of stabilizing copper was replaced by high strength high conductivity microcomposite Cu-Nb material. The results of description of the electric field-current density characteristics E(J,epsiv,B,4.2 K) are presented. To describe experimental database E( J) versus strain and magnetic field the relation is used containing four fitting parameters. Three parameters,namely: C, Tc(0) and Bc2(0, epsiv) describe. Additional parameter characterizes the smoothness of E( J). Good agreement of experiment and calculation has been obtained.

E(J)

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).

Characteristics in the ITER Type

Multifilamentary wires based on ternary Nb- Ti- Ta alloys with 55 and 4620 filaments have been fabricated by several processing routes. Ternary alloys with 12.4 and 20.4 wt. % Ta were used having Tc 8.99 and 8.70 K. Critical currents of the wires have been measured at 5–13.5 T and at 4.2 and 2.2 K. Critical current densities of the wires with 60–40 µm filaments and 7–3.5 µm filaments, which were prepared under the identical conditions, were compared for both the compositions.