Study of Low Loss Experimental Superconducting Nb-Ti Wires to be used in FAIR Magnets

For the effective operation of the Facility for Antiproton and Ion Research (FAIR) magnet system, a new class of superconducting wires with high current carrying capacity and low energy losses is needed. Special requirements are formulated to the wires for this application. Diameter of Nb-Ti filaments has to be about 3 , critical current density has to be above 4500 A/mm² (at 2 T; 4.2 K) and filament twist pitch should be as small as possible without a degradation of critical current density. These wires with small filaments should contain a resistive (Cu-0.5%Mn) inter-filament matrix to reduce inter-filament coupling current losses and OF copper outside and inside the filamentary region to provide required stabilization. The comparative study of low losses superconducting Nb-Ti wires of different designs was performed. These experimental wires intended for use in FAIR model magnets were fabricated by double stacking method. The experimental Nb-Ti wires conform to the abovementioned requirements. This paper presents current characteristics, hysteresis losses and other properties of experimental low losses Nb-Ti wires. The benefits of each design are discussed.