Design, fabrication and properties of 1 T (4.2 K) Bi-2223 high- superconducting prototype magnet

Abstract

Ag-sheathed monofilamentary Bi-2223 high-temperature superconducting tapes were fabricated using the `powder-in-tube' (PIT) method with powders of (x = 0, 0.14, 0.24) chemical composition. The highest critical current density and the shortest time for Bi-2223 phase completion were found in tapes with x = 0.24. The x = 0.24 composition tapes with a reproducible critical current density of between and for short samples, with averages of for 4 m long tapes and for 100 m long tapes at 77 K in the self-field, have been produced using the conventional PIT method. A test magnet was designed and constructed by stacking together eight pancake coils. Each pancake coil was made by the react-and-wind technique with three co-wound tapes on an 18 mm diameter mandrel. Dimensions and parameters of this magnet are as follows: height, 46 mm; winding inner diameter, 18 mm; winding outer diameter, 56 mm; total number of turns, 290. Total conductor length in the magnet was m. The coils were connected in series and then tested at 4.2 K and 77 K. The field constant at mid-plane of the magnet, determined by introducing a Hall probe into the bore of the magnet, was 29 G s and the magnet could generate a 0.12 T magnetic field at 77 K, and 1.07 T at 4.2 K. Eight pancake coils were stacked in a testing magnet using the two coils in parallel connection and four double-coils in series connection method; this makes it possible to use a mix of good and less good tapes and to use fully the critical current of each tape. A detailed investigation of the -B properties and -strain characteristic of the Bi-2223 tapes as design parameters and properties of the test magnet has been carried out.