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Because of their high critical fields, high-Tc superconductors (HTS) are considered to be the only solution to dramatically increase the highest fields of NMR magnets. We have successfully demonstrated that a 500 MHz HTS/LTS NMR system with a Bi-2223 innermost coil could be used for solution NMR in a driven-mode operation. As the next step, the upgrade of the 920 MHz NMR system installed at the Tsukuba Magnet Laboratory is underway. The innermost Nb3Sn coil has been replaced by a Bi-2223 coil. The coil was fabricated as a layer-wound coil using five Bi-2223 conductors reinforced with bronze tapes. It was connected in series with the outer Nb3Sn and NbTi coils. The magnet is expected to generate a field of 24.2 T (1.03 GHz of ^1H resonance frequency) at an operating current of 244.4 A. The test using the Bi-2223 coil and the outer Nb3Sn coils in combination was successfully carried out. The coil has been installed in the 1.03 GHz NMR magnet. Its cooling and operation are scheduled to take place within Fiscal Year 2010. [ABSTRACT FROM AUTHOR]

In this study, we investigated in field properties of high-Tc superconductor (HTS) tapes electrically as well as mechanically. Metallic reinforced Bi-2223/Ag superconductor tapes were used in this work. The critical current (Ia), which is highly dependent on the magnetic field, was measured using fields applied parallel and perpendicular to the tape surface. The conductor was exposed to fields of up to 28 T at 4.2 K. In order to confirm the performance of tapes in practical NMR operation, Ic was also measured around 2 K. The conductor was wound on a large diameter bobbin and mechanical properties were then measured as the coil current was increased. Finally, we verified the conductor properties from coil Ic and maximum stress/strain of it. [ABSTRACT FROM AUTHOR]

The electromagnetic stress distribution inside a HTS insert is one of the key issues for construction of a high field high/low temperature superconductor (HTS/LTS) magnet. The r · J · B formulae is widely used for the stress calculation of the coil, due to its simplicity. However, the assumption of this calculation makes it impossible to consider the effects of the bobbin, an epoxy impregnated structure, on stress of the coil. In this work, stress analysis methods are reported. The governing equation defined from the force equilibrium state was adopted and used to analyze what the stress of the HTS coil wound with Bi2223/Ag conductor. The validness of the stress analysis method was confirmed by comparison with experimental results, especially in the coil with epoxy impregnation. The numerical and experimental procedures are described and both results are discussed. [ABSTRACT FROM AUTHOR]

For the development of high magnetic field application using high temperature superconductor (HTS), Bi-2223/Ag tape is one of the promising materials because of its high current capacity and upper critical field. However, Bi-2223/Ag tape shows very strong anisotropy and significant deterioration of critical current in the magnetic field. To explore the possibility of HTS in high field applications, we evaluated the critical current and index value of Bi-2223/Ag conductor in high magnetic field. The Bi-2223/Ag tape was characterized as a function of increasing and decreasing field. The temperature dependence was also examined lower than 4.2 K. All measurements were carried out with hybrid magnet system up to 30 T and the experimental results are reported. [ABSTRACT FROM AUTHOR]

High-temperature superconductors (HTS) are considered to be indispensable to realize NMR magnets that exceed 1 GHz owing to their high critical current densities even in high magnetic fields exceeding 20 T. Feasibility studies of the > 1-GHz NMR magnet with the HTS inner coil have been reported. HTS conductors are brittle, and it is not easy to apply to superconducting coils such as the inner coils of the > 1-GHz NMR magnet. Investigations into the mechanical properties of HTS coils are quite important. The hoop stress is an important factor in magnet design. Bi-2223 conductors are most promising because they are commercially available and can be obtained with lengths of more than 1,000 m. Double pancake coils with an inner diameter of 260 mm wound from Bi-2223/Ag conductors of the Sumitomo DI-BSCCO (high-Ic type and high-strength type) were fabricated to evaluate the hoop stress dependence of the critical current of the coil. The double pancake coils were tested using the 14-T superconducting magnet with a room temperature bore of 400 mm in diameter at the Tsukuba Magnet Laboratory (TML). The critical current of the high-Ic test coil was 164 A, where the hoop stress was estimated at 323 MPa. The critical current decreased to 140 A after energizing the coil above a hoop stress of 300 MPa. The high-strength test coil burst at a hoop stress of approximately 200 MPa. [ABSTRACT FROM AUTHOR]

In order to obtain a large magnetic force environment using a commercially available superconducting magnet with a room-temperature bore, a new cryostat cooling a high-temperature superconductor (HTS) bulk cylinder with a G-M cryocooler down to approximately 20 K was developed. The cryostat was inserted so that the bulk cylinder might be located at the mid-plane of a 12-T cryocooler-cooled magnet. In the first experiment, the cylinder was cooled from room temperature to 21 K at 5.0 T. The backup field was then decreased to 0 T. A field of 4.9 T was maintained along the Z-axis inside the cylinder. The second experiment was carried out from a backup field of 11.5 T. The HTS bulk cylinder maintained the magnetic flux down to about a backup field of 7.6 T, at which point the superconducting state of the cylinder was lost in a brief period. The experimental data exhibit good accordance with the calculation results. In the calculation, the minimum BdB/dz of -1029 T²/m was estimated to be generated along the Z-axis. As that of the magnet is -564 T²/m at 12 T, the enhancement of the magnetic force with the HTS bulk cylinder was confirmed. [ABSTRACT FROM AUTHOR]

The performance of a flux concentrator using an YBCO oxide superconductor was tested to raise the steady state magnetic field generated by the existing magnet. This concentrator was composed of an outside hollow cylinder and a pair of half cylinders that goes in and out in the outside cylinder. This flux concentrator generated additional magnetic field more than 1.6 T for an applied magnetic field 28 T. [ABSTRACT FROM AUTHOR]

We have proposed new applications of bulk high-temperature superconductors in high magnetic fields. High-temperature superconductors, such as BSCCO or YBCO, maintain their superconductivity over 30 T at 4.2 K. A field-cooled superconducting hollow cylinder traps the magnetic flux inside itself. A field-cooled superconducting solid cylinder traps in the interior of it. An increase of the applied magnetic field induces shielding current in the interior of the cylinder to maintain the magnetic flux constant. By suitably arranging the cylinders, we can concentrate the magnetic flux and enhance the gradient of the magnetic field. In order to confirm these concepts, we performed experiments using bulk YBCO cylinders. The cylinders are made of Yba2Cu3O7-x quasisingle crystals containing Y2BaCuO5 particles. Hollow and solid cylinders were employed to concentrate the magnetic flux. Using three hollow cylinders, the concentrated magnetic field of 0.49 T was observed in the applied magnetic field of 10.14 T. The concentrated magnetic field of 0.64 T was observed for the solid cylinders in the applied magnetic field of 10.24 T. The magnetic flux concentration was observed even in the high magnetic field over 20 T. [ABSTRACT FROM AUTHOR]

Examines the persistent-mode operation of a high temperature superconducting magnet cooled by a cryocooler. Thermal conductance; Decay behaviors; Temperature increase of the magnet due to persistent current switch.