Design, fabrication and performance of a 1.29 T Bi-2223 magnet

Abstract

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.

AC analysis of a high temperature superconductor coil with short circuits

“…The coil is a basic unit for a magnet used in a maglev demonstration vehicle [7]. The coil is designed primarily for a non-eddy current structure, therefore any usage of metallic material is absent from the main structure including the copper bobbin, which is frequently used not only as a skeleton but also as a cooling path in some DC magnets [8][9][10]. The absence of the bobbin in this design also shortens the distance between the iron core and HTS coils, and thereby reduces the flux leakage as much as possible.…”

Simulation of ferromagnetic shielding to the critical current of Bi2223/Ag tape under external fields

“…Following the development of the over pressure processing technique, the critical current I c (self-field) of the tape has been significantly improved by a factor of 30-40% [1,2], reaching a value of 200 A in 77 K. When the tape is used in applications, an auxiliary way is often used to increase the I c further by introducing ferromagnetic shielding (FS), which can guide the flux away from the superconductor region. In [3][4][5][6], iron yokes installed at the end of the coil were used to reduce the field at the outmost pancake, a place exposed to the strongest perpendicular field. This technique was also widely adopted in tape applications.…”

The design and performance of a Bi-2223/Ag magnet cooled by a single-stage cryocooler

“…The substantially increased current-carrying capacity and reduced I c anisotropy of Bi-2223 at decreased temperatures (20-30 K) enable the production of cryogenfree magnet systems [8,9]. Cryogen-free systems with a temperature window 20-30 K allow generating much higher magnetic fields than using liquid nitrogen; no cryogen is required, the cooling efficiency is high, and the system is much more economical than that for 4.2 K. A 1.29 T laboratory sized Bi-2223 magnet operating at 4.2 K has been fabricated from six epoxy resin impregnated double-wound pancakes of inner diameter 40 mm made by the R&W technique [10]. Cryogenfree Bi-2223 systems have been made using stacked pancake coils producing fields of 7 T [11] at around 20 K. Recently, Richens et al [12] have presented Bi-2223 coil successfully operated by conduction cooling by a two-stage cryocooler in the temperature range 12-50 K. Their thermal stability studies have shown that thermal run-away is sufficiently controlled and damage can be readily prevented.…”