Test Results of Two Small, High-Temperature Superconducting Coils
Electrical Measurements were performed on two high-temperature superconducting coils made by American Superconductor Corporation. One coil measured 24-mm i.d., 59-mm o.d, 50-mm long, and used 85-m long Y-124 tape conductor. The other coil measured 29-mm i.d., 44-mm o.d., 43-mm long, and used 35-m long Bi-2223 tape conductor. We obtained V-I curves from room to helium temperature by using a variable temperature cryostat cooled by helium gas in external fields up to 4 T. Without an external field, the better performing Bi-2223 coil had a critical current, I c , of 14.1 A (2,820 A/cm2 over the conductor) at 4.2 K and 1.8 A (360 A/cm2) at 77 K. At 4 T, the I c was 4.9 A (980 A/cm2) at 4.2 K and 2.0 A (400 A/cm2) at 50 K. Reduced critical current, I c (B)/I c (0) vs. field plots indicated that a single smooth curve could fit all the data up to 50 K. The reduction in critical currents with external fields for the Y-124 coil was more than 80% at i T. For the Bi-2223 coil, it was about 42% at 1 T and about 61% at 4 T.
KeywordsCritical Current Critical Current Density Solenoid Coil Final Heat Treatment Composite Wire
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