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We propose a new device built from a bulk superconductor to enhance the magnetic flux density within a high-field superconducting magnet. The high-temperature superconductor (HTS) bulk application, named the magnetic field amplifier, was constructed from four pieces of Gd–Ba–Cu–O superconductor. The field amplifier has a unique configuration of the bulk superconductor, which suppresses the current on the periphery of the bulk induced by external field variation. We experimentally demonstrated that the field was effectively amplified at the center of the HTS bulk device. By increasing the background field from 12 to 13 T in field-cooling mode, a magnetic flux density of 14.76 T was obtained at the center of the amplifier. The observed multiplication factor was 2.76, corresponding to external field variation. A configuration to further improve efficiency and reduce size is also presented. [ABSTRACT FROM AUTHOR]

We investigate the AC loss behavior in MgB2 wires using numerical calculations based on the finite element analysis (FEM). The governing equation for the system was formulated using a magnetic vector potential and an electric scalar potential, taking into account the non-linear, field dependence of the critical current density (Jc). The model incorporated the results of measurements of the Jc-B of for a real MgB2 wire. For this, we directly measured the Jc-B characteristics according to the external fields as well as various temperatures. A transport current loss analysis was performed on the MgB2 wire for a wide range of transport current values and different temperatures. The magnetization loss was also calculated as a function of the external magnetic field and temperature. For both type of losses, the numerical results were found to be in good agreement with those obtained by theoretical calculations, thus verifying the validity of the model. [ABSTRACT FROM AUTHOR]

Shielding of magnetic fields (magnetic shielding) by rare earth-based REBCO coated conductors with a highly oriented superconducting layer was measured. The shielding of magnetic fields was measured using a Hall effect sensor installed between bundles consisting of commercial REBCO conductors 12 mm in width. Measurements of the shielding of magnetic fields by other commercial high-Tc superconductors were performed for comparison. The shielding of magnetic fields was found to depend on the number of conductors in the bundle and the route of the applied magnetic fields and was observed even for fields over 10 T. In steady magnetic fields, a temporal change in the shielding of magnetic fields, that is, a decay of shielding currents induced in conductors against applied magnetic fields, was measured. The temporal change of the shielding of magnetic fields exhibited the behavior typical of high-Tc superconductors, as explained by the flux creep model. Remanent magnetic fields measured in the experiments of the shielding of magnetic fields suggest that the bundle can be used as a magnet. A quasi-bulk magnet consisting of 100 Zr-doped Zr:REBCO conductors could hold over 3 T at 4.2 K. [ABSTRACT FROM AUTHOR]

Using high-Tc superconductors (HTS) is considered to be the only solution to dramatically increase the highest fields of NMRmagnets because of their high critical fields. However, it is not easy to apply HTS to an NMR spectrometer (HTS-NMR) because a persistent-mode operation with HTS cannot satisfy the field stability of 0.01 ppm/h at present. To overcome this problem, we are now developing an HTS-NMR spectrometer in a driven-mode operation. As the first step, a layer-wound coil was fabricated with bronze-reinforced Bi-2223 conductors. Instead of the Nb3Sn coil, the Bi-2223 coil was installed as the innermost part of an existing NMR magnet. The magnet operated at a field of 11.7 T with a highly stabilized power supply. NMR measurements were carried out, and it was demonstrated that the quality of the multi-dimensional NMR spectra on the protein was equivalent to that obtained with a persistent-mode system. The next step will be to demonstrate its usefulness as a high-field NMR system. The upgrade of the 920 MHz NMR system installed at the Tsukuba Magnet Laboratory is underway. Its innermost coil is scheduled to be replaced by a Bi-2223 layer-wound coil for 2010. Its target field is 24.2 T (1.03 GHz). [ABSTRACT FROM AUTHOR]

Mg addition improves Tc, Birr, and Ic of the Nb3 Sn formed by diffusion reaction between Nb and Ag-Sn alloy, when the diffusion reaction is performed below 650°C. The obtained superconducting properties are similar to those of the bronze-processed Nb3Sn. The formation temperature of Nb3 Sn is reduced by the Mg addition. By using OM, SEM, and field emission type EPMA, we could not measure the thickness of Nb3Sn Iayers, which may be thinner than 0.5 μm. It is not clear that the Mg addition increases the formation rate of Nb3Sn. However, the Nb3Sn layers should have very high Jc. The attainable overall Jc of the Nb3Sn wire are as high as those of the bronze-processed Nb3Sn wire without Ti and Ta additions, although the optimization of the cross-sectional configuration of Nb and Ag-Sn-Mg in the wire has not yet performed. Therefore the potential of the Nb3Sn conductor made by the new process seems to be very attractive for the practical applications. [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]

A workbench magnet that generates magnetic fields on a room-temperature (RT) plate was developed. The magnet did not have a RT bore. The improvement of accessibility to magnetic fields has made several types of processing and measurement easier. The magnet provides external fields, magnetic fields in the vicinity of the top of a winding, of a solenoid coil on the RT plate. The external fields depend strongly on the gap between the RT plate and the top of the winding. The magnet was a cryocooled superconducting magnet with a 1-W GM cryocooler at 4 K. The magnet successfully generated magnetic fields of over 3 T at the center of the RT plate. The magnet could generate magnetic fields more than twice the surface magnetic fields of permanent magnets with the same accessibility. [ABSTRACT FROM AUTHOR]

We investigated the superconducting properties of Nb3Sn formed through the diffusion reaction between Nb and Ag-Sn alloys, including Ag-9at%Sn ductile fcc phase and Ag-(12–16)at%Sn ductile ζ phase alloys, and Ag-24at%Sn brittle e phase alloy. We fabricated single-core and multi-core composite wires by the rod-in tube and powder-in-tube processes. The composite wires were heat treated at 650–900°C to form Nb3Sn filaments. With increase of Sn content in the Ag-Sn alloy cores, the superconducting properties of the Nb3Sn composite wires were improved. Tc and Bc2 (4.2 K) values for the Nb/Ag-Sn wires are similar to those for the Nb/Cu-Sn. However the Ic values are relatively small, due to their very thin Nb3Sn layers below 0.4 μm. Ag is apparently not effective to increase the formation rate of Nb3Sn layer. By using the 200- and 40000-core wires, Tc and Bc2 (4.2 K) values were increased by 0.5–1 K and 2–5 T, respectively for these multifilamentary wires, while from 10 to 500 times larger Ic, (4.2 K) were obtained for the wires. The typical values for Tc and Bc2 (4.2 K) are 16.5–17.7 K and 16–21 T, respectively. The addition of 5at%Cu to Ag-Sn alloys improves their superconducting properties. [ABSTRACT FROM AUTHOR]

A new 52-mm warm-bore resistive insert for a hybrid magnet was designed and constructed at the Tsukuba Magnet Laboratory (TML) of the National Institute for Materials Science (NIMS). This magnet successfully generated a peak magnetic flux density of 35.5 T at the operating current of 34.88 kA and 367.5 V with a background field of 14.05 T. To supply the high magnetic fields for more time in the 52-mm warm bore, an axially cooled three-coaxial-coil structure and a staggered layout of the elongated cooling holes were adopted for Bitter disks after a parameter survey that was conducted to consider a reduction in the operating electric power. Disks were stacked in a modified Weggel scheme on a turntable with a rotating angle controlled by the stacking data of each coil. The innermost coil was connected electrically in series with the two outer coils connected in parallel. The Bitter disks used in the coils were made from two kinds of Cu-Ag plates. The magnet is now in operation for users. [ABSTRACT FROM AUTHOR]

The water-cooled insert magnet of the TML hybrid magnet successfully generated 37.9 T in a 32-mm room- temperature bore with a 14.02 T buckup field generated by a superconducting outsert magnet. At that magnetic field, the maximum electric power for the insert magnet was 13.35 MW. This Bitter-type insert magnet is divided into three coaxial coils, and the innermost coil consists of two coaxial coils. The inner coil is connected in series with the outer two coils connected in parallel. The Bitter plates for the outermost coil were made of GlidCop AL-25, and those for the other coils were made of hard-worked Cu-Ag plates. The thickness of the Cu-Ag plates was 0.40 mm, and the average 0.2 % yield strength was about 810 MPa at 373 K. [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]

Magnetic field direction often greatly influences material properties, such as critical current densities of tape-shaped superconductors. To determine the influence of this parameter, an object is usually rotated in a fixed magnetic field, which is not always effective. We are developing a variable-fieId-direction superconducting magnet that can change its field direction continuously in a two-dimensional plane. Two sets of split-pair coils are placed perpendicular to each other, and the perpendicular magnetic fields generated by each split-pair coil are superimposed. By independently controlling the operating current of each split-pair coil, we can continuously change the direction of the superimposed magnetic field. Four solenoid coils were wound with Nb-Ti conductors. This magnet is designed to rotate a field of 1 T. The field homogeneity is estimated to be less than 1 % in a 10 mm-diameter sphere volume. This is a conduction-cooled superconducting magnet employing 4K-GM refrigerators. We constructed a cryostat with two types of room-temperature bores and conducted a cooling test without solenoid coils and supporting structures was conducted. [ABSTRACT FROM AUTHOR]

In this paper, we propose new applications of bulk high-temperature superconductors in high magnetic fields. High-temperature superconductors, such as Bi[sub 2]S[sub r]2CaCu[sub 2]O[sub 8+d] (BSCCO) or YBa[sub 2]Cu[sub 3]O[sub 7-x] (YBCO), maintain their superconductivity over 30 T at 4.2 K. A field-cooled superconducting hollow cylinder traps the magnetic flux inside 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 hollow cylinders. The cylinders are made of YBa[sub 2]Cu[sub 3]O[sup 7-x] quasi single-crystals containing Y[sub 2]BaCuO[sub 5] particles. They have an inner diameter of 5 mm, an outer diameter of 10 mm, and a height of 10 mm. Using three hollow cylinders, a magnetic concentration of 0.49 T was observed in an applied magnetic field of 10.14 T. The energized hollow cylinder with a shielding current modify surrounding magnetic fields and magnetic force fields. A magnetic force field enhanced by using a hollow cylinder was calculated numerically for an applied magnetic field of 10 T and estimated to exceed 6000 T²/m. [ABSTRACT FROM AUTHOR]

We developed a device to enhance magnetic force fields generated by superconducting magnets. We named this device a "magnetic force booster". A magnetic force booster consists of rings and disks that are made from ferromagnetic materials and is designed to enhance magnetic force fields without destroying their uniformity. We used a magnetic force booster for a commercial superconducting magnet capable of generating a central magnetic field of 10 T and a magnetic force field of 400 T² /m in order to observe the perfonnance of a magnetic force booster. The result confinned that the magnetic force booster could enhance the magnetic force field generated by the commercial superconducting magnet to higher than 1360 T² / m. This result was in good agreement with an analytical result. [ABSTRACT FROM AUTHOR]

We investigate the performance of a magnetic lens in very high magnetic fields exceeding 24 T. The magnetic lens is composed of Gd-Ba-Cu-O superconducting bulk materials. The unique configuration of the magnetic field amplifier, which consists of slits and electrical insulation in the bulk, allows the magnetic flux density to be further enhanced by a background magnet. In field cooling operation, the external magnetic field was varied ∼4 T from 24.2 to 28.3 T and a total magnetic flux density of 30.35 T was found at the center of the device with a background magnet. The magnetic lens additionally increased the magnetic flux density by 2.05 T due to the lens effect. However, it was also observed that the bulk was partially quenched when the external field was varied. This partial quench and recovery of the bulk magnet is considered to be one factor that limits the performance of the lens effect. Finally, we are able to generate a substantial magnetic flux density of 2 T under very high magnetic field because we can obtain such high-field without further electrical power. [ABSTRACT FROM AUTHOR]

Abstract: The direct production of Nb3Al superconducting coils using the combinational technology of ‘cold spray’ as physical deposition and ‘electron beam’ as surface modification has been proposed. Using this method, the helical line of the Nb3Al superconductor is produced directly on a cylinder without conventional wiring process. In order to prove the possibility of direct coil production, we first made flat-plate and cylindrical samples, and then examined the characteristics as superconductor. The flat-plate samples showed the phase transition in magnetization and the characteristics of superconductivity when the output powers of the electron beam were over 800W at a beam speed of 3m/s and 1200W for 6m/s. It was confirmed that a 10-turn single-layer coil with a ϕ40mm diameter and a length of 50mm generated a magnetic field of 2.7mT at 20.5A. [ABSTRACT FROM AUTHOR]

Abstract: We have commenced a project to develop a beyond-1GHz solution NMR spectrometer using a HTS coil. Due to a small residual resistance present in the HTS conductor and joint resistance between conductors, a stable persistent current sufficient for NMR measurements is unlikely. Therefore, a current has to be supplied to the HTS coil from an external power supply. The ripple of an external power supply causes a field fluctuation which must be stabilized. In this study we show results of NMR measurements using a 500–600MHz NMR in such an external current mode: the field fluctuations are stabilized by an internal 2H lock. The field fluctuation from the external power supply comprises a major field fluctuation component at low frequencies, 0.003–0.005Hz, and superimposed minor field ripples at 2Hz and 50Hz. The former limits the time interval of the internal 2H lock, while the latter generates sidebands in the NMR spectrum. Sideband and baseline noise are controlled by appropriate selection of the feedback loop parameters of the lock. The quality of the 1D-solution NMR spectra observed in external current mode is equivalent to that obtained in persistent current mode. However, if the feedback loop time is as short as the gradient pulse width, refocusing of the NMR signal is lost and NMR peaks disappear. The 2D-NOESY and the 2D-HSQC spectra of ubiquitin in an external current mode have been acquired. The quality of the 2D spectra is equivalent to those obtained in persistent current mode; i.e. the internal 2H lock operates stably over an experimental time interval of 40–50min. To realize a beyond-1GHz NMR spectrometer, further investigations must be made of (i) the long term stability of a DC power supply, (ii) the enhancement of the compensation field limit for the internal 2H lock, (iii) the extension of the helium refill time interval, and (iv) a method to correct the field homogeneity in the external current mode. [Copyright &y& Elsevier]