Monofilament for the production of 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 monofilament for the production of a superconducting wire, the monofilament comprising:
 a powder core that contains at least Sn and Cu;   an inner tube that encloses said powder core, said inner tube being made of Nb or of an alloy containing Nb;   an outer tube in which said inner tube is disposed, wherein an outer side of said inner tube is in contact with an inner side of said outer tube, said outer tube being made of Nb or of an alloy containing Nb; and   a cladding tube in which said outer tube is disposed.   
     
     
         2 . The monofilament of  claim 1 , wherein said cladding tube has a hexagonal outer cross-section and a round inner cross-section. 
     
     
         3 . The monofilament of  claim 1 , wherein said inner tube has a round inner cross-section and a round outer cross-section and said outer tube has a round inner cross-section and a round outer cross-section. 
     
     
         4 . The monofilament of  claim 3 , wherein
   1.2 ≦D   outside   outertube   /D   outside   innertube ≦2.0 with  D   outside   outertube : outer diameter of the outer tube and  D   outside   innertube : outer diameter of the inner tube.
   
     
     
         5 . The monofilament of  claim 3 , wherein  4 ≦W outertube /W innertube ≦50 with W outertube : wall thickness outer tube and W innertube : wall thickness inner tube. 
     
     
         6 . The monofilament of  claim 1 , wherein said powder core has a content of 2 weight % to 12 weight % of Cu, 3 to 9 weight % of Cu or said powder core contains elementary Cu powder. 
     
     
         7 . The monofilament of  claim 1 , wherein said powder core is compacted in said inner tube or has a density of at least 40% or of at least 50% of a theoretical density. 
     
     
         8 . The monofilament of  claim 1 , wherein said powder core contains NbSn 2  and/or Nb 6 Sn 5  and/or elementary Sn. 
     
     
         9 . The monofilament of  claim 1 , wherein said inner tube and/or said 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. 
     
     
         10 . The monofilament of  claim 1 , wherein said inner tube and said outer tube are produced from different materials. 
     
     
         11 . The monofilament of  claim 1 , wherein said cladding tube is made of Cu. 
     
     
         12 . A method for producing the monofilament of  claim 1 , 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).   
     
     
         13 . The method of  claim 12 , wherein the cladding tube already has a hexagonal outer cross-section prior to step c). 
     
     
         14 . A method for producing a precursor of a superconducting wire using the monofilament of  claim 1 , the method 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;   c′) extruding and/or drawing the wire cladding tube containing the bundled and drawn monofilaments, thereby obtaining the precursor of the superconducting wire.   
     
     
         15 . The method of  claim 14 , 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. 
     
     
         16 . The precursor of a superconducting wire produced by the method of  claim 14 . 
     
     
         17 . A method for producing a superconducting wire using the precursor of  claim 16 , 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.   
     
     
         18 . The method of  claim 17 , 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. 
     
     
         19 . The superconducting wire produced by the method of  claim 17 .