Generation of 24.0 T at 4.2 K and 23.4 T at 27 K with a high-temperature superconductor coil in a 22.54 T background field

Abstract

The 4.2 K and 27 K current-carrying performance of a high-temperature superconducting (HTS) coil was measured in background fields up to 22.54 T generated by a hybrid magnet (Hybrid III) at the MIT Francis Bitter National Magnet Laboratory. The coil, 40 mm winding i.d., 108 mm winding o.d., and 113 mm high, consists of 17 double pancakes, each wound with silver-sheathed BSCCO-2223 tapes. Each pancake is the product of a react-and-wind method. In total, the test coil contains ∼1200 m of BSCCO-2223 conductor weighing ∼7 kg. Prior to the measurements in Hybrid III, the coil was tested in zero background field in the temperature range from 4.2 to 77 K. It was coupled to a Gifford–McMahon type cryocooler and at 15 K generated a peak field of 2.1 T; at 18 K, it generated 1.9 T, operating continuously for ∼50 h. In a 22.54 T background field of Hybrid III, the coil reached critical currents of 116.5 A ([Jc]sc, critical current density based on the BSCCO cross-sectional area only, of 261 A/mm) at 4.2 K and 67 A ([Jc]sc=150 A/mm) at 27 K, establishing record net fields at respective temperatures of 24.0 and 23.4 T for HTS magnets. These currents correspond to overall winding current densities of 47 and 27 A/mm. High-field critical current data for short samples of the tape of the same formulation at 4.2 and 27 K are also presented. Although a [J]sc of 261 A/mm at 24 T and 4.2 K for the test coil is significantly less than ∼600 A/mm for the short samples at the same operating point, if factors such as length, bending, and even differences in defining critical current are considered, the coil and short samples have nearly the same critical current performance. Electromagnetic stresses do not seem to have any negative effects on coil performance. Record fields of 24.0 and 23.4 T were achieved after the test coil had experienced, over a period of 15 months, 20 thermal cycles between room temperature and cryogenic temperatures.

Study of High Field Superconducting Solenoids for Muon Beam Cooling

“…Several coil inserts made of Bi 2 Sr 2 Ca 2 Cu 3 O 10+x (Bi-2223) and Bi 2 Sr 2 CaCu 2 O 8+x (Bi-2212) superconductors with the bore contribution of up to 5 T were produced and successfully tested with background coils in 24-25 T configurations [2]- [4], demonstrating the feasibility of HTS inserts.…”

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

“…In short samples, J c of 6.9×10 4 A cm −2 [3] and 7.3×10 4 A cm −2 [4] has been achieved in zero-field at 77 K. High-field applications rely on the use of high-performance tapes of kilometre lengths. In the Bi-2223 system, this level of performance is now being realized with J c of 1.2 × 10 4 A cm −2 reported over 1260 m [5], 1.8 × 10 4 A cm −2 over 250 m [6] and over 2 × 10 4 A cm −2 achieved in 1200 m [7], 1000 m [8] and 400 m [9] lengths at 77 K in self-fields. It is expected that J c will increase yet further, perhaps by an order of magnitude [10], as our understanding of tape processing improves.…”

“…The high current-carrying capacity of Bi-2223 up to 30 K [7,11,12] enables the production of compact cryogen-free magnet systems. Cryogen-free systems are attractive because: (i) easy operation is facilitated since no cryogen is required; (ii) cooling efficiency at 20 K is approximately five times higher than at 4 K making refrigeration more economical; (iii) thermal stability and fast magnet sweep rates are possible because the specific heat of the tapes is about two orders of magnitude higher at 20 K than at 4 K. Cryogen-free Bi-2223 systems have been fabricated using stacked pancake coils producing fields of 7.25 T [13] and 7 T [14] at around 20 K. The high upper critical field of Bi-2223 also facilitates the production of high-field inserts.…”

High-temperature superconductors in high-field magnets

“…For metallic superconductors it is assumed that the operating current is limited by the lowest value of J e (B) at a small, localized section of the magnet 34 . This assumption is only accurate for conductors with high n-values.…”

“…The first significant HTS insert coil was developed by Sumitomo, tested at the Francis Bitter National Magnet Lab at MIT and published in 1995 [34]. This sizeable coil with a useable bore size generated 1.5 T in a background magnet for a central field of 24 T, a value that would not be exceeded until 2003 with the 5T insert.…”