SUPERCONDUCTIVE ELEMENT CONTAINING Nb3Sn

摘要

A superconductive element containing Nb₃Sn, in particular a multifilament wire, comprising at least one superconductive filament ( 8 ) which is obtained by a solid state diffusion reaction from a preliminary filament structure ( 1 ), said preliminary filament structure ( 1 ) containing an elongated hollow pipe ( 2 ) having an inner surface ( 3 ) and an outer surface ( 4 ), wherein said hollow pipe ( 2 ) consists of Nb or an Nb alloy, in particular NbTa, wherein the outer surface ( 4 ) is in close contact with a surrounding bronze matrix ( 5 ) containing Cu and Sn, and wherein the inner surface ( 3 ) is in close contact with an inner bronze matrix ( 5 ) also containing Cu and Sn, is characterized in that the inner bronze matrix ( 5 ) of the preliminary filament structure ( 1 ) encloses in its central region an elongated core ( 6 ) consisting of a metallic material, said metallic material having at room temperature (=RT) a thermal expansion coefficient alpha_core<17*10^-6K^-1, preferably alpha_core<=8*10^-6 K^-1, said metallic material having at RT a yield strength R_p0.2>300 MPa, said metallic material having at RT an elongation at rupture A>20%, and wherein the metallic material of the core ( 6 ) is chemically inert with respect to the material of the inner bronze matrix ( 5 ) up to a reaction temperature T of the solid state diffusion reaction. This element has improved superconductive properties in a large volume fraction of its superconductive filaments, in particular a high critical temperature T_c and a high critical magnetic filed strength B_c2, and is mechanically stable enough for commercial applications such as magnet coils.