BEHAVIOUR OF MULTIFILAMENTARY Nb-Ti CONDUCTORS WITH VERY FINE FILAMENTS UNDER A.C. MAGNETIC FIELDS

Abstract

Long lengths of multifilamentary Nb Ti composites, which comprise several thousands. 5 to 1 micron-diameter filaments, have been manufactured. These composites, with a Cu-Cu Ni mixed-matrix and some of them with pure Cu Ni between the filaments, carry hight current densities up to 1.95 105 A/cm2 at 5 Teslas. Their structure provides a good magnetic stability and leads to strongly reduced 50 Hertz losses. These results allow to consider alternators with superconducting rotor and armature windings and, in a general way, they open very new prospects for industrial applications of superconductivity in fast pulsed magnets and in A.C. current devices

Current limitation using high T/sub c/ materials

“…Moreover if the principle is simple a lot of problems have to be solved before the idea becomes an industrial system. Several teams have worked on the development of superconducting low T, current limiter [3,4,5]. The most advanced program is led by GEC Alsthom together with Alcatel Alsthom Research and EDF with an industrial dlemonstration on the French 63 kV network planned for 1998 [6].…”

Drawing a single nanofibre over hundreds of microns

“…Such interactions between molecules can also give rise to supramolecular structures in solution as is the case with amphiphiles molecules [12]. Compared to the mass fabrication of nanofibres such as nanotubes [2], superconductor wires [14] or inorganic fibre [15], the great advantage of our pulling procedure is that the fibres can be produced one at a time and at a given position on the surface. The positioning precision depends on the end section of the micropipette used which is below 200 nm.…”

Influence of proximity effect on the hysteresis loss of ultrafine filamented superconducting composites

“…The thickness Cu layer between filaments in CCN70 is 0.29 ~m and the CuNi layer is 0.66 ~m thick. If we assume that the effective layer thickness is the sum of each layer thickness weighted by its coherent length, the following formula holds: (1) Then the effective filament spacing of CCN70 becomes 0.7 ~m. Hence we expect that the coupling due to the proximity effect does not occur in these composites , which is seen clearly in the figure.…”

“…However, in 1983, Dubots et a1. [1] first showed the possibility of applying superconductors to the utility frequency range. They reduced the diameter of an NbTi filament to the order of 1 ~m with an appreciable J , c and decreased the hysteresis losses to the level of two orders of :nag',j tude smaller than a typical value at that time.…”

“…An illu st r a tion of the dis tribution of th e order pa r ame ter in a multifilamentary composi t e N normal matrix (2) When the f ilament diameter becomes smaller than 0.1 ~m, the hysteresis loss increases in spite of smaller filament and B p becomes smaller than the case (1).…”