DEVELOPMENT OF HIGH-FIELD CHEVREL PHASE SUPERCONDUCTING WIRES USING LOW TEMPERATURE PROCESSING

NEW SUPERCONDUCTING WIRES WITH SUPERIOR UPPER CRITICAL FIELDS (BC2) AND HENCE EXCELLENT CURRENT-CARRYING CAPABILITIES IN HIGH MAGNETIC FIELDS ARE REQUIRED TO BUILD HIGH-FIELD (>20 TESLA AT 4.2 K) SUPERCONDUCTING MAGNETS. IN ADDITION TO BISMUTH-BASED OXIDE SUPERCONDUCTORS, CHEVREL-PHASE MATERIALS ARE CONSIDERED AMONG THE MOST PROMISING CANDIDATES FOR SUCH HIGH-FIELD APPLICATIONS. COMPARED WITH HIGH CRITICAL TEMPERATURE (TC) OXIDE SUPERCONDUCTORS, CHEVREL-PHASE MATERIALS POSSES NOT ONLY VERY HIGH BC2 BUT ALSO NEAR-ISOTROPIC CRITICAL CURRENT DENSITY (JC) CHARACTERISTICS. MOREOVER, BECAUSE SILVER-SHEATH IS NOT REQUIRED AS IN PREPARING OXIDE SUPERCONDUCTING WIRES, CHEVREL-PHASE SUPERCONDUCTING WIRE CAN BE PRODUCED BY STANDARD INDUSTRIAL PROCESSING TECHNIQUES AND CAN BE REINFORCED AGAINST INCREASED LORENTZ FORCES IN HIGH MAGNETIC FIELDS. THE PHASE I PROJECT IS CONDUCTING A RESEARCH AND DEVELOPMENT EFFORT TO DEVELOP MONOFILAMENTARY LEAD-TIN-MOLYBDENUM-SULFUR (PB-SN-MO-S) QUATERNARY CHEVREL-PHASE SUPERCONDUCTING WIRES THROUGH SPECIAL LOW TEMPERATURE POWDER METALLURGY ROUTES. THE EMPHASIS IS ON THE SYNTHESIS OF HOMOGENOUS, FINE-GRAINED, AND LOW-OXYGEN-CONTAMINATED PB-SN-MO-S CHEVREL-PHASE MATERIALS AT LOW TEMPERATURES (NOT GREATER THAN 1,000 DEGREES CENTIGRADE) WITH GOOD GRAIN CONNECTIVITY. THE MONOFILAMENTARY CHEVREL-PHASE WIRE WILL BE FABRICATED WITH THE CONVENTIONAL WIRE PROCESSING TECHNIQUES AVAILABLE IN INDUSTRY. IN ADDITION TO TC AND JC TESTS, MICROSTRUCTURAL ANALYSES ARE BEING CONDUCTED. THE PROSPECTS FOR COMMERCIAL DEVELOPMENT OF A CHEVREL-PHASE MULTIFILAMENTARY SUPERCONDUCTING WIRE IS BEING EVALUATED ON THE BASIS OF THE RESULTS FROM THE PHASE I PROJECT.