Michiya Okada

Flux pinning in single Tl-layer 1223 superconductors

Abstract The presence of pinning centers in high temperature superconductors (HTSCs) is a prerequisite for obtaining a high critical current density ( J c ) in a magnetic field. We have discovered that, perhaps more generally, HTSCs having only a single layer between the superconducting copper layers (for example the YBaCuO or TlSrCaCuO systems) can possess effective pinning centers that are absent in the double layer cases. Several samples prepared by a partial melt process, with the nominal composition (Tl 0.5 Pb 0.5 ) 1 (Sr 0.8 Ba 0.2 ) 2 Ca 2 Cu 3 O 9 , showed the high intragrain J c , by the magnetization method, greater than 2 × 10 4 A/cm 2 at 77 K and 1 T. This result suggests that more effective pinning centers exist in the (1223) phase of the modified TlSrCaCuO system (ref. [1]). We propose an explanation why both YBa 2 Cu 3 O 7 and (1223) of TSCCO contain useful pinning centers, whereas both Bi- and Tl-double-layer superconductors do not. Effective pinning, in this case greater for single layers rather than double layers, is related to the strength of the superconductive order-parameter in these layers intervening the CuO layers.

A Round Table Discussion on

This paper summarizes a round table discussion on MgB2 held in the evening of September 20, 2005, during the 19th International Conference on Magnet Technology. The discussion, by the panelists and the audience, includes both material features and applications of MgB 2 as well as views on the commercial prospects for MgB2 magnets

rm MgB_2

Ba2YCu3O7-δ tapes were fabricated by cold rolling. The critical current density Jc apparently depended on the thickness of the tape and increased markedly with decreasing tape thickness. The maximum Jc of 3330 A/cm2 at 77 K in a zero magnetic field was achieved in an Ag-sheathed BYCO tape, 0.06 mm in thickness. The presence of a 20 mT magnetic field reduced the Jc value by 1/100.

Toward a Wide Market or a Niche Production?—A Summary

Development of a 1 GHz superconducting NMR magnet is in progress at the Tsukuba Magnet Laboratory (TML) of the National Research Institute for Metals (NRIM). This magnet will contain a BSCCO inner coil, which should generate a central field of 23.5 T in a backup field of 21.1 T. In order to accomplish this targeted field, we fabricated two Bi-2212 double-pancake coils (Coil A and Coil B). They were installed in the high-field superconducting magnet system at the TML/NRIM. Their performance was measured in a backup field of 18 T. Coil A was made of 20 double-pancakes wound with Ag sheathed Bi-2212 tape conductors. Ag-Mg tape was co-wound for mechanical support. Its winding was 147 mm in outer diameter and 220 mm in height. It generated a central field of 21.4 T in a clear bore of 61 mm. Coil B was located inside Coil A. Its 6 double-pancakes were wound with Bi-2212 tape conductors reinforced with Ag-Mg-Ni alloy sheath. The outer diameter and height of the winding were 48 mm and 63 mm, respectively. Coil B generated the highest field of 23.4 T in a backup field of 21.4 T. This study confirmed that the present performance of the Bi-2212 coils had already satisfied the required conditions for the inner coil of the 1 GHz NMR magnet from the viewpoint of high-field generation.

Fabrication of Ag-Sheathed Ba-Y-Cu Oxide Superconductor Tape

Ag-sheathed Tl2Ba2Ca2Cu3O10 tapes with a Tc of 120 K were fabricated by cold rolling. The tapes annealed at an optimized condition yielded Jc=6700 A/cm2 (77 K/0 T) and 100 A/cm2 (77 K/1 T). The Jcs of the TBCCO tapes were twice as high as those of YBCO tapes in the absence of external magnetic fields, and about ten times as high as those of YBCO in the presence of magnetic fields.

Generation of 23.4 T using two Bi-2212 insert coils

Abstract The paper reports the first successful fabrication and test of a MgB 2 coil. We have fabricated 15 m long MgB 2 -superconducting wires by a powder-in-tube method using Ni-sheath without any heat treatments during the processing. The MgB 2 /Ni tape has a good uniformity of high J c value (500–600 A/mm 2 at 4.2 K and 0 T) along the tape length as well as a nice bending tolerance. I c degradation of the tape occurred at the bending strain of as high as 1%. Using a 10 m long Ni-sheath tape, we have made a small solenoidal coil with 80 turns to be tested in liquid helium. The coil showed a typical training effect, I c increasing by repeating the excitation, and the highest I c value we obtained was 105 A, which generated the central field of 0.13 T.

Ag-sheathed Tl−Ba−Ca−Cu−O superconductor tape with Tc∼ 120 K

Recent achievements in the newly-developed Bi-2212/Ag round-shaped wire with tape-shaped multifilaments are summarized. The new round-shaped wire includes 126-1320 tape-shaped filaments with triple rotation symmetry, having a good crystal alignment of Bi-2212 in each filament. We refer to the new wire as ROSATwire , (ROtation-Symmetric Arranged Tape-in-tube wire). The ROSATwire fabrication process markedly improved productivity and lowered the cost, and also improved the transport Jc of the wire. The Ic and Jc reached values greater than 340 A and 1000 A mm-2 , respectively, at 28 T and 4 K. Insulated wires of over 400 m length, 2 mm in diameter, are now available and ready for magnet winding. Several solenoid magnets with a 130-160 mm outer diameter and 100-600 mm height are now under fabrication.

Fabrication and transport properties of MgB2 wire and coil

A high-field HTSC conduction cooled magnet system is considered to be the most promising system for superconducting magnets of the next generation. The authors have been developing a 10 T Bi-2212/Ag solenoid magnet system with a room temperature bore of 50 mm. This system consists of inner, mid and outer coils. The coils are designed to generate 10 T at 10 K with Bi-2212/Ag ROSATwire (ROtation-Symmetric Arranged Tape-in-tube wire). This wire shows almost isotropic field dependence of J/sub c/ and ease of solenoid winding. The details of design of the system have been completed, and inner test coils and also a conduction cooling system have been built. Approximately a total of 3 km long Bi-2212/Ag ROSATwire has been employed for windings of the coils. In this paper, design of the magnet system, the preliminary results of trial operation of the inner coil and test result of the conduction cooling system are presented.

Development of Bi-2212/Ag round-shaped wire and magnet application

Round 100 m long class MgB/sub 2/ mono-core wires with Fe/Cu composite sheaths were successfully fabricated using an in situ PIT method. The J/sub c/ of the round MgB/sub 2//(Fe/Cu) wires reached 380 A/mm/sup 2/ at 4.2 K and 6 T, and exceeded 2500 A/mm/sup 2/ at 3 T. High areal reduction of the MgB/sub 2/ core was found to be effective in improving the transport properties of the MgB/sub 2/ wires. Using a 58 m long MgB/sub 2//(Fe/Cu) wire, we made a solenoid coil with 495 turns and tested it in liquid helium. The dimensions of the MgB/sub 2/ coil were 30 mm in inner diameter, 48 mm in outer diameter, and 50 mm in height. The I/sub c/ of the coil reached 214 A, which corresponds to a J/sub coil/=238 A/mm/sup 2/ and a core-J/sub c/=1420 A/mm/sup 2/. The coil generated a magnetic field at a center of B/sub o/=2.05 T and a maximum magnetic field of B/sub m/=2.17 T.

10 T conduction cooled Bi-2212/Ag HTS solenoid magnet system

On the title of this paper (page L623 and contents): Bi-2211/Ag is a misprinted symbol. It should be corrected to Bi-2212/Ag.