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The design and fabrication procedure of a laboratory-scale Bi-2223 tape superconducting magnet with a bore of 40 mm and a maximum field of 1.29 T at 4.2 K is presented. The magnet comprises six resin impregnated double-wound pancakes of bore diameter 40 mm fabricated via the react-and-wind route. Critical current density (J c ) measurements have been made as a function of magnetic field, angle and strain at 4.2 K and 77 K on short samples. In zero field, the critical current density for the superconducting cross-sectional area of the tape was 8.3 × 10 4 A cm −2 (4.2 K) and 1.18 × 10 4 A cm −2 (77 K). The electric field-current density characteristics of all the components of the coils when individually energized or with the whole magnet energized have been measured. Comparison between short sample measurements and performance of the magnet show that minimal additional damage occurred beyond the ∼20% that was produced by the bending strain during the wind-and-react fabrication procedure and the ∼10% variation of the long length J c of the tape. Sufficient detail is provided for the non-specialist to assess both the use of potential brittle superconducting tapes for magnet technology and to construct a laboratory-scale magnet.

Aktract -Four double wound pancakes with inner diameters of 98 mm have been successfully fabricated with multifilamentary Bi-22231Ag tape using the react and wind technique. Two pancakes were impregnated with wax and the other two with resin. The pancakes have been tested at 77 K producing critical current (13 values up to 14.5 A and index of transition values (n) of up to 11.4. The field profiles produced by the pancakes have been modelled. The I, field dependence of short samples of the component Bi-22231Ag tape has been studied. I, is most sensitive to field when the field is parallel to the c-axis of the tape, reducing I, from 28 A to 13.2 A between 0 T and 30 mT. Although the bending strain of the tape in the coil is -0.396, the fabrication procedure for the pancakes has produced very little handling damage to the tapes. It is demonstrated that the I, of the coils is almost entirely self field limited. I. blTRODUCTIONSince the discovery of high temperature superconductors (HTS) in 1986, significant work has gone into improving the properties of the materials. We have now reached a period when conductors can be produced over long lengths [1,2] making large scale magnet applications realistic. Multifilamentary HTS cuprates remain the most likely candidates, in particular the Bi-2223 phase due to the high J, properties that can be produced in long lengths using powder route processing [2-41. There are three main areas of applications development for these conductors; 1) High temperature, low field applications (B < 1 T) allowing relatively cheap liquid nitrogen to be used a coolant; 2) Medium field magnets (2 T B < 10 T) operating at temperatures of 20-30 K, enabling the easy use of cryocoolers and 3) Very high field inserts ( > 20 T) for use at 1.8-4.2 K temperatures, taking advantage of the high J, and B, values. For example a lo00 m Bi-Z223/Ag tape was used to produce Manuscript This work was supported by BICC Limited and EPSRC. a magnet [2] which produced a self-field of 4 T at 4.2 K, 1 T in 20 T background field and 0.37 T in a 23 T background field [SI.In this paper, we report on the design and fabrication of four double wound pancake coils from Bi-2223 multifilamentary tape using the react and wind route. Two of the pancakes have been impregnated with wax and two with resin. The self field generated for the coils has been calculated. The bore for these coils is 98 mm which produces a bending strain on the tape of about 0.3%. Since strain measurements on short samples show that Jc markedly decreases at strain values of typically 0.3% [6,7J, the handling of the tapes during the fabrication procedure must be kept to a minimum. The voltagecurrent characteristics have been measured for all sections of the pancakes in liquid nitrogen in self-field. In addition, Jc measurements have also been made on short samples of the tape used to fabricate the coils at 77 K in fields up to 300 mT. These data allow us tu assess the performance of the coils.Section I1 describes the fabrication procedure of the pancakes. Sec...