Method for producing a monofilament for an Nb3Sn superconductor wire

Abstract

A monofilament ( 1 ) for the production of a superconducting wire ( 20 ) has a powder core ( 3 ) that contains at least Sn and Cu, an inner tube ( 2 ), made of Nb or an alloy containing Nb, that encloses the powder core ( 3 ), and an outer tube ( 4 ) in which the inner tube ( 2 ) is arranged. The outer side of the inner tube ( 2 ) is in contact with the inner side of the outer tube ( 4 ) and the outer tube ( 4 ) is produced from Nb or from an alloy containing Nb. The outer tube is disposed in a cladding tube. The superconducting current carrying capacity of the superconducting wire is thereby improved.

I claim: 
     
         1 . A method for producing a monofilament for a superconducting wire, the monofilament comprising:
 a powder core that contains at least Sn and Cu;   an inner tube that encloses the powder core, the inner tube being made of Nb or of an alloy containing Nb;   an outer tube in which the inner tube is disposed, wherein an outer side of the inner tube is in contact with an inner side of the outer tube, the outer tube being made of Nb or of an alloy containing Nb; and   a cladding tube in which the outer tube is disposed, the inner tube having a round inner cross-section and a round outer cross-section and the outer tube having a round inner cross-section and a round outer cross-section, wherein 4≦W outertube /W innertube 50 with W outertube :wall thickness of the outer tube and W innertube :wall thickness of the inner tube,   
       the method comprising the steps of:
 a) filling the powder core into the inner tube; 
 b) drawing, following step a), the inner tube, thereby compacting the powder core; 
 c) inserting the outer tube into the cladding tube; and 
 d) inserting, following step b), the drawn, filled inner tube into the outer tube, wherein step c) is performed prior to or after step d). 
 
     
     
         2 . The method of  claim 1 , wherein the cladding tube has a hexagonal outer cross-section and a round inner cross-section. 
     
     
         3 . The method of  claim 1 , wherein
 1.2≦D outertube   outside /D innertube   outside ≦2.0 with D outertube   outside :outer diameter of the outer tube and D innertube   outside :outer diameter of the inner tube.   
     
     
         4 . The method of  claim 1 , wherein the powder core has a content of 2 weight % to 12 weight % of Cu, 3 to 9 weight % of Cu or the powder core contains elementary Cu powder. 
     
     
         5 . The method of  claim 1 , wherein the powder core is compacted in the inner tube or has a density of at least 40% or of at least 50% of a theoretical density. 
     
     
         6 . The method of  claim 1 , wherein the powder core contains NbSn 2  and/or Nb 6 Sn 5  and/or elementary Sn. 
     
     
         7 . The method of  claim 1 , wherein the inner tube and/or the outer tube are produced from an alloy containing Nb and containing Ta and/or Ti, have a summed content of at least 0.5 weight % of Ta and/or Ti or have with a summed content of maximally 10 weight % of Ta and/or Ti. 
     
     
         8 . The method of  claim 1 , wherein the inner tube and the outer tube are produced from different materials. 
     
     
         9 . The method of  claim 1 , wherein the cladding tube is made of Cu. 
     
     
         10 . The method of  claim 1 , wherein the cladding tube already has a hexagonal outer cross-section prior to step c). 
     
     
         11 . A method for producing a precursor of a superconducting wire using the monofilament produced by the method of  claim 1 , the method further comprising the steps of:
 a′) drawing one or more of the monofilaments to produce monofilaments having a hexagonal outer cross-section;   b′) bundling a plurality of drawn monofilaments in a wire cladding tube; and   c′) extruding and/or drawing the wire cladding tube containing the bundled and drawn monofilaments, thereby obtaining the precursor of the superconducting wire.   
     
     
         12 . The method of  claim 11 , wherein, in step a′), the monofilaments already have a hexagonal outer cross-section of the cladding tube and a round outer cross-section of the outer tube prior to drawing, wherein the drawn monofilaments also have a hexagonal outer cross-section of the cladding tube and a round outer cross-section of the outer tube after drawing. 
     
     
         13 . The precursor of a superconducting wire produced by the method of  claim 11 . 
     
     
         14 . A method for producing a superconducting wire using the precursor of  claim 13 , the method comprising the steps of:
 d′) mechanically deforming the precursor or winding the precursor to form a coil; and   e′) temperature-treating the deformed precursor or temperature-treating the deformed precursor at a maximum temperature of 700° C. or less, wherein Nb from the inner tube and the outer tube reacts with Sn from the powder core to form Nb 3 Sn.   
     
     
         15 . The method of  claim 14 , wherein temperature treatment is terminated in step e′) before a reaction front that advances to an outside has reached a boundary surface between the outer tube and the cladding tube. 
     
     
         16 . The superconducting wire produced by the method of  claim 14 .