Kazuhide Tanaka

Generation of 23.4 T using two Bi-2212 insert coils

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 and transport properties of MgB2 wire and coil

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.

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

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.

Fabrication and transport properties of MgB/sub 2/ mono-core wire and solenoid coil

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.

Relaxation of Trapped High Magnetic Field in 100 m-long Class

This paper reports on the relaxation of trapped magnetic field in a MgB2 solenoid coil in PC mode operation. For PC mode operation, we fabricated a closed loop circuit with a MgB2 coil, a PCS and some superconducting joints. The MgB2 coil was fabricated employing a 100 m-long PIT processed MgB2 wire using a wind & react method. The critical current Ic of the coil reached 166 A and the coil was able to generate a maximum magnetic field of about 2.5 T at 4.2 K without an external field. The PCS was fabricated employing a long NbTi wire stabilized Cu-Ni alloy. The joints were fabricated between MgB2 and NbTi conductor, between NbTi (PCS) and NbTi conductor. The resistance of all fabricated joints was estimated to be less than 1.0times10-13 Omega. In PC mode operation with the closed loop circuit, a magnetic field of 1.46 T was trapped for about 50000 s (above 12 hr.) without any detectable decay. These results demonstrate the possible use of the MgB 2 superconductor for applications such as MRI superconducting magnet

rm MgB_2

The feasibility study of a superconducting level sensor for liquid hydrogen with a magnesium-diboride (MgB2) wire is carried out from an experimental point of view. The sample wire consists of a mono-cored MgB2 superconductor and a cupronickel sheath, and several potential taps are attached to it at even intervals in order to understand the position of a threshold between the superconducting and resistive states roughly. The fabricated sensor is vertically located in a glass dewar vessel with an infill of liquid hydrogen, and the position of a preselected potential tap is adjusted by eye and hand to liquid level before starting a new measurement. Simulated operations with constant currents finally yield the future possibilities as the level sensor for liquid hydrogen with MgB2 wire although the fabricated sensor has a few problems at present. In order to improve the performance of the sensor, the specifications required for MgB2 wires will be reported elsewhere by applying the stability theory in superconductor composites and by simulating the operation with a numerical code.

Solenoid Coil in Persistent Current Mode Operation

A new Bi-2212/Ag round-shaped wire with tape-shaped multifilaments has been successfully developed. The wire includes 126-960 tape-shaped filaments with triple rotation symmetry, having a good crystal alignment in each filament. We refer to the new wire as ROSATwire, (ROtation-Symmetric Arranged Tape-in-tube wire). Since the ROSATwire structure yields complete symmetrical arrangement of the tape-shaped filaments, it eliminates the need for a rolling machine, but allows us to use a drawing or extrusion machine. We found that the present wire fabrication process markedly improves not only productivity and lowers cost, but also enhances the transport J/sub c/ of the Bi-21212/Ag wire. The I/sub c/ and J/sub c/ reached >340 A and 1000 A/mm/sup 2/ at 28 T and 4 K.

Fundamental investigation of a superconducting level sensor for liquid hydrogen with MgB2 wire

We designed and fabricated two types of composite wires with 6 MgB2 filaments. One is a Cu-sheathed Nb-barrier wire and the other is a CuNi-sheathed Ta-barrier wire. The transverse-field losses of the trial wires were measured with a standardized pickup coil system in liquid helium. We evaluated the observed AC losses using two structural models, a multifilament conductor model and a hollow-cylindrical one. For the CuNi-sheathed Ta-barrier wire, the AC loss property can be explained by the usual model of multifilament conductors. Further reductions in AC loss can be expected by making the filaments thinner. For the Cu-sheathed Nb-barrier wire, theoretical considerations suggest the multifilament structure behaves as a hollow-cylindrical superconductor in the AC loss property. Thus, we need to pay particular attention to designing the barrier material for reduction in the AC loss.

A new symmetrical arrangement of tape-shaped multifilaments for Bi-2212/Ag round-shaped wire

This paper focuses on the magnetization characteristics of technical Nb3Al conductors, in particular the minimization of their hysteresis loss and low-field instability. Unlike the case of Nb3Sn wire fabrication, the Nb3Al wire is fabricated by a phase transformation process, in which it is believed that the Jc properties of the transformed Nb3Al phase do not depend on the filament size or shape, but rather are principally controlled by the rapid heating and quenching or transformation conditions. However, the rapid heating and quenching process forces us to use high-melting-point metals like niobium as the matrix. The use of Nb strongly affects the magnetization because of its superconductivity in low fields. In this paper, the magnetization properties of several kinds of technical Nb3Al conductors, including Ta matrix wires, were studied. The use of Ta was effective in suppressing low-field instability. In addition, we propose a new process to further minimize the filament diameter by a re-stacking (RS) method, whereby the rapidly quenched strands are re-stacked into a stabilizing material tube and co-drawn. This process leads to a very fine multifilamentary structure with a filament diameter of less than 15xa0µm, thereby substantially reducing the magnetization, as compared with high-performance Nb3Sn wires, e.g. RRP Nb3Sn wire. The ± 3xa0T hysteresis loss of the RS Nb3Al conductor was 370xa0mJxa0cm−3 and the non-Cu Jc (12xa0T, 4.2xa0K) of the conductor was 1350xa0Axa0mm−2. These values meet the ITER strand specification.

AC loss properties of MgB2 multifilament wires

Over 2 km-long ROSAT wires with round-shaped cross-section have been successfully fabricated to a prototype magnet having the same dimensions as the actual insert magnet of a 1 GHz-NMR spectrometer. 400 m-long ROSAT wires with rectangular shaped cross-section have also been manufactured without any degradation of the current carrying capacity through wire processing. Another prototype magnet has been fabricated with the rectangular ROSAT wire. For each magnet, the present study demonstrates the feasibility of processing both 1 m-long Bi-2212/Ag leads and ROSAT wire-NbTi wire joints at each end of the leads to the magnet construction.