Controlled Overpressure Research Articles

Overview of the recent performance of DI-BSCCO wire

Sumitomo Electric has been developing the silver-sheathed Bi2223 multi-filamentary wires since the discovery of Bi-based superconductors. DI-BSCCO (Dynamically-Innovative BSCCO) is the high performance wires produced with the controlled-overpressure (CT-OP) sintering technique. The recent R&D activities have enabled to produce the 1000m-long wires with Ic of 200A and the maximum Ic reached 250A at 77K by short sample. Besides, the fine control of the carrier density with the non-stoichiometric oxygen enhanced the in-field Ic performances at lower temperature. At a magnetic field of 3T applied normal to wire surface, the Ic of 280A at 30K, and 420A at 20K were successfully achieved. To meet the growing needs for various high temperature superconducting applications, Type HT wire with high mechanical strength and Type G wire with low thermal conductivity have been developed.

Effects of low level laser therapy (LLLT) on pressured human osteoblasts: A histomorphologic and quantitative study

Previous research has investigated the effects of LLLT during titanium implantation, tooth movement and bone graft using deproteinized bovine bone and recognized that these circumstances were nothing more than intentional controlled overpressure against static cells since this controlled trauma could affect cell function/malfunction, or cell recovery/apoptosis. The present preliminary study was conducted to prove if LLL would influence cell viability and cell function after excessive damage, which is enough to diminish cell numbers and distort the features of cells. Our aim is to evaluate whether low level laser irradiation (LLLi) could be helpful in the recovery of traumatized osteoblasts (pressure damaged cells) by observing the morphology and the survival rate of those cells. This model used bone cell cultures which were traumatized by a pressure with 250 G of centripetal force and observed their response to such trauma and low level laser irradiation. In this experiment, a Ga-Al-As diode LLL (IMPRA-ORT, NDLux, Seoul, KOREA) was used with a wavelength of 808 nm, a focus of 14 × 24 mm, which was wide enough to cover the whole dish surface or well within at least 2 times radiation, and an output of 100 mW. Statistical analysis showed a higher recovery rate of damaged osteoblasts in the radiation group than the non-radiation group (p < 0.05). The nonradiation group had a very poor proliferation rate in comparison to the control group (p < 0.05) in every time period. In the control group, actin filaments showed a random orientation and cell process branched variously around each cell. In contrast, compressed cells, these patterns were turned into thicker and shorter cytoskeletons. As time progressed, every living cell recovered from the severe stress and recovered both form and function. In summary, the present study showed the capacity of LLLT to aid the recovery of the cell skeleton and affect cell viability on overpressured osteoblasts. These results may contribute toward a better understanding of the effect of LLLT on the recovery of cells after trauma. In addition, our results demonstrated that LLLT could be used in the field of bone tissue engineering to traumatized bone conditions and repair large bone defects such as bone graft and implant installation.

Recent R&amp;D progress on DI-BSCCO wires with high critical current properties

Abstract Sumitomo Electric has been developing the silver-sheathed Bi2223 multi-filamentary wires since the discovery of Bi-based superconductors. DI-BSCCO is the superconducting wire with high and uniform critical current properties produced using the controlled-overpressure (CT-OP) sintering technique. The present commercial DI-BSCCO can provide the uniform high critical current, I c, up to 180 A with length over 2000 m, and recently over 200 A with length over 1000 m were produced successfully, resulting from the improvement and control of the microstructure in Bi2223 multi-filaments. The short trial wires of several meters have exhibited the highest I c over 240 A at 77 K in self-field (corresponding to 580 A per 1 cm-width). Besides, the optimization of carrier density after CT-OP have led to further enhancement of I c, reached 250 A at 77 K in self-field. All the derivative products also have uniform critical current properties over entire length even after lamination with the reinforcing metals. The performances of DI-BSCCO can meet the growing needs for various applications of high temperature superconductor like high in-field applications, such as magnets and motors. The recent progress in transport properties of commercial DI-BSCCO and R&D short trial wires is shown.

Present Status and Future Perspective of Bismuth-Based High-Temperature Superconducting Wires Realizing Application Systems

Among a series of high-temperature superconducting materials that have been discovered to date, (Bi,Pb)2Sr2Ca2Cu3O10-x is the best candidate for superconducting wires that are long with commercial productivity, and critical current performance. In particular, the controlled overpressure (CT-OP) sintering technique gave us a 100% density of (Bi,Pb)2Sr2Ca2Cu3O10-x portion, which leads to robustness, increase in critical current, and mechanical tolerance. Many application prototypes are already verified and are being evaluated worldwide. Current leads for large magnets and magnetic billet heaters are already commercial products. Commercial applications for power cables, motors for ship propulsion and electric vehicles, and many kinds of magnets are promising in the near future.

Recent Progress in High Performance Ag-Sheathed Bi2223 Wire (DI-BSCCO®)

Sumitomo Electric has been developing the silver-sheathed Bi2223 multi-filamentary wires since the discovery of Bi-based superconductors. DI-BSCCO is the high performance wires produced using the controlled-overpressure (CT-OP) sintering technique. The present commercial DI-BSCCO can provide the uniform high critical current, Ic, up to 180 A with length over 2000 m, and recently 200 A were succeeded to be obtained by the same kind of 1000 m length wires, resulting from the improvement and control of the microstructure in Bi2223 multi-filaments. The short trial wires of several meters have exhibited the highest Ic over 240 A at 77K in self-field (corresponding to 580 A per 1 cm-width). Besides, the optimization of carrier density after CT-OP led to further enhancement of Ic, reached 250 A. All the derivative products also have uniform critical current properties over entire length even after lamination with the reinforcing metals. The performances of DI-BSCCO can meet the growing needs for various application of high temperature superconductor like high in-field applications, such as magnets and motors. The recent progress in transport properties of commercial DI-BSCCO and R&D short trial wires is shown.

Angular, Temperature, and Strain Dependencies of the Critical Current of DI-BSCCO Tapes in High Magnetic Fields

High critical current density ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Jc</i> ) DI-BSCCO Bi-2223 superconducting tape has been developed by Sumitomo Electric Industries (SEI) using the Controlled Over-Pressure (CT-OP) technique to improve the texturing and densification. Further enhancement of the mechanical properties has been obtained using lamination. We have investigated the effect of magnetic field and field orientation on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Jc</i> for a series of test DI-BSCCO tapes at 77 K and 4.2 K under tensile and compressive strains. These critical current data are strongly influenced by the anisotropy of Bi-2223, the texturing of the tape and its architecture. The magnetic field and angular dependence of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Jc</i> at 77 K can be described using a simple anisotropic exponential magnetic field model which includes the effects of the two-dimensionality and grain misalignment in these composites. The variation in the normalized <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> with respect to the strain is linear over the reversible range of strain where the gradient of the strain dependence is independent of temperature and field. The reversibility of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is extended further into the compressive regime after <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation by compression.

Longitudinal Uniformity of Commercial Bi2223 Tapes Characterized by Scanning Hall-Probe Microscopy

We investigated remanent field distributions for commercial Bi2223 tapes with length of 1 m and high critical current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of 150 A (77 K, self-field) developed by Sumitomo Electric Industries (SEI) Ltd., by scanning Hall-probe microscopy (SHM) with an active area of 50μm × 50μm. All tapes are prepared by powder-in-tube process and sintered by controlled-over pressure (CT-OP) processing at final sintering stage. A bare tape and a 3-ply reinforced one with stainless tape laminations were used for measurements. The distribution of remanent field B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rz</sub> in perpendicular to broader face of a magnetized tape was measured using SHM, at a fixed distance of 0.5 mm away from a tape surface. Although absolute B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rz</sub> values in a reinforced tape were 10% lower than bare one, the shape of B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rz</sub> profile along a lateral direction of a tape was hardly affected by reinforcement and uniformly distributed along a length of each tape. Moreover, we cut away 15 cm piece sample from each tape and measured B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rz</sub> profile before and after double-sided bending with a bending diameter of 30 mm. The results indicated that degradation in both intensity and longitudinal uniformity of B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rz</sub> for a reinforced tape is much smaller than for a bare one.

Recent R&D progress on DI-BSCCO wires with high critical current properties

Sumitomo Electric has been developing the silver-sheathed Bi2223 multi-filamentary wires since the discovery of Bi-based superconductors. DI-BSCCO is the high performance wires produced with the controlled-overpressure (CT-OP) sintering technique. The present commercial DI-BSCCO can provide the uniform high critical current, Ic, up to 180A over 2000m, and recently 200A were succeeded to obtain with the same kind of 1000m-long wires, resulting from the improvement and control of the microstructure in Bi2223 multi-filaments. The short trial wires of several meter have exhibited over 240A as the highest Ic at 77K, self-field (corresponding to 580A per 1cm-width) according with high Tc over 112K. Besides, the optimization of carrier density after CT-OP led to further enhancement of Ic, reaching 250A. All the derivative products have also uniform critical current property over the entire length even after lamination with the reinforcements. The performances of DI-BSCCO can meet the growing needs for various high temperature superconducting applications involving high in-field properties, such as magnets and motors. The recent progress on Ic including in-field properties along with the remarkable findings on the performances of DI-BSCCO will be shown.

Development of a Bi-2223 HTS Magnet for 3T MRI System for Human Brains

We are developing a cryogen-free high temperature superconducting (HTS) magnet system for a compact 3T MRI system for human brains. In the conceptual design, the magnet system consists of 5 main coils that are layer windings of Bi-2223 tapes. The magnet system will have 500 mm room temperature bore and be operated at 20 K using G-M cryocoolers. The target field is 3 T ±5 ppm for 250 mm (dia,) and 200 mm (length) volume. All the coils will be connected in series and operated in driven mode. Controlled overpressure (CT-OP) processed Bi-2223/Ag tapes which are reinforced with Cu-alloy laminations are to be used for these coils. We investigated Ic-B-T performance in detail for short samples of the tape. We fabricated and tested five small layer-wound coils using the tape (38.4 ~ 46.2 m piece for each coil). Each small coil could be energized up to its expected current that was calculated using the short sample performance and the coil parameters. The maximum electromagnetic force (hoop stress) reached 137 MPa, and caused no degradation in the coil performance. These results show that our layer-winding techniques and the conductor performance (Ic-B-T and homogeneity along length) can be applicable and suitable for our 3T MRI magnet.

Effect of number of filaments on the critical current density in multifilamentary Bi-2223 tape

The critical current property of Bi2Sr2Ca2Cu3Ox(Bi-2223) silver-sheathed tape has been remarkably improved by application of ConTrolled Over Pressure (CT-OP) process with adjusting temperature and oxygen partial pressure. For further improvement of the property of Bi-2223 tapes, the effect of number of filaments on the critical current density Jc was investigated. It was found that Jc was higher and its decrease with increasing magnetic field was weaker in the tape with larger number of filaments. In addition, the irreversibility field Bi increased with increasing filament number. The field-angle anisotropy Jc(0°)/Jc(90°) of the tape with the largest filament number was smallest, where the field-angle was measured from the a–b plane. However, the out-of-plane misorientation angle is fairly small in this tape. Hence, the low field-angle anisotropy in this tape seems to be attributed to improved superconductivity in the block layers in the superconducting region near the interface with silver matrix.

Study on critical current distribution in CT-OP Bi-2223 tape based on the scanning Hall probe magnetic microscopy

Critical current (Ic) of a Bi-2223 tape fabricated by controlled-overpressure (CT-OP) sintering method has been attained up to 200 A-class in recent years. However, current limiting factors have not been fully clarified yet. In this study, we have investigated local current distributions in a CT-OP Bi-2223 tape by using the scanning Hall probe magnetic microscopy. As a result, it has been found that large sheet current flows in the center of the sample. Even though the influence of self-field is taken into account, there is a clear difference of local Ic across the width. The maximum sheet current value in the center of the tape is 400–450A/cm when we applied the bias current of 100A, which is equal to the Ic at around 87K. This value is equivalent to 800–900A/cm at 77K taking into account the value of Ic. Furthermore, such current distribution continues uniformly in length direction. From these results, we have concluded that improvement of current uniformity across the tape width is the effective way to enhance critical current for the present CT-OP Bi-2223 tape. Our results show the feasibility for 300 A-class Ic at 77K.

Evaluation of critical current density in multifilamentary Bi-2223 tapes with different lead compositions

The critical current property of Bi-2223 silver-sheathed tape has been remarkably improved by application of ConTrolled Over Pressure (CT-OP) process with adjusted temperature and oxygen partial pressure. For further improvement of the property of Bi-2223 tapes, the effect of variation in the lead composition was investigated. It was found that the critical current density J c was higher and its decrease with increasing magnetic field was weaker in the tape with higher lead composition than other tapes in a parallel magnetic field. On the other hand, although J c of this tape was higher, its decrease with increasing magnetic field was stronger in a normal magnetic field. This seems to be attributed to the larger condensation energy density due to the carrier doping by lead and to the better crystal axis alignment.

Performance of an over-pressure processed Bi-2223/Ag/SUS tape and a small layer-windingcoil

We have successfully demonstrated the utility and potential of Bi-2223/Ag tapesfabricated by a CT-OP (controlled-overpressure) process. In this paper, we report theIc–B–T performance of a short tape with stainless steel lamination and energizing-test results of asmall layer-winding coil in an external magnetic field ranging from 0 to 12 T and attemperatures ranging from 4.2 to 90 K. The coil is a solenoid layer-winding of a135 m piece of Bi-2223/Ag tape with stainless steel lamination on both sides. Thedimensions of the conductor are 2.7 mm in width and 0.25 mm in thickness, including a0.02 mm thick stainless steel lamination on both sides. A short sample cut from thesame tape has critical currents exceeding 76 A, 307 A and 438 A at 77 K, 30 K and4.2 K, respectively, in self-field. The winding was performed using a ‘react & wind’technique and the resultant coil had 597 turns and dimensions of 65 mm (innerdiameter), 83 mm (outer diameter) and 60 mm (winding height). In 12 T, 4.2 K, thecoil-Ic is 191 A, which adds 1.42 T to the external field. In the present coil, thecoil-Ic is controlled by the field component in the coil’s radial direction generated by the coil itself. TheIc values of the coil agree very well with those estimated from the short sample’s performanceand field distribution. The results indicate that the homogeneity of the Bi-2223 conductoris very good throughout its whole 135 m length.

Fabrication of a working Bi-2223 superconducting magnet cooled by liquid nitrogen

A practical Bi-2223 superconducting magnet, working in liquid nitrogen (L.N2), was designed and fabricated. Bi-2223 tape with a critical current of 147A was prepared by a controlled overpressure (CT-OP) process at 77.3K in self-field. Ten double-pancake coils were resistively connected by copper terminals. The bore diameter was 54mmϕ, the magnet outer diameter was 122mmϕ, the height of the magnet was 124mm, and the weight of the magnet was about 3kg. The maximum magnetic field at the center of the bore was 0.48T with an operating current of 50A. The experimental results agree well with design predictions calculated by finite element method. AC operation was also performed, and no distortion of the voltage waveform was observed. Therefore, this Bi-2223 superconducting magnet is a suitable replacement for copper magnets designed for applications in science and technology.

Homogeneity of Superconducting Properties in Controlled Overpressure Processed Bi2223 Tapes

Recently, due to the controlled overpressure (CT-OP) sintering technique, performances such as critical current, n-value, unit-length and mechanical strength of Ag sheathed (Bi, Pb)2Sr2Ca2Cu3Ox (Bi2223) tapes were significantly enhanced. In order to investigate the origin of these improvements, we evaluated the distribution of the superconducting properties inside the tape along the width. We selected several kinds of CT-OP processed Bi2223 tapes and each tape was divided into three parts (one central part and two edge parts). We performed transport (critical current Ic) and magnetic (susceptibility) measurements. We found that a slight inhomogeneity in superconducting properties still remains even in the highest performance tape, whose Ic is about 200 A at 77 K. Critical current densities Jc are lower at the edge part than those of the central parts. These results indicate that we can expect and achieve further improvements of CT-OP processed Bi2223 tape by enhancing the performance of the edge parts of the tape.

Evaluation of field-angle anisotropy of critical current in multifilamentary Bi-2223 tapes prepared by CT-OP process

The critical current property of Bi-2223 silver sheathed tape has been significantly improved by application of ConTrolled Over Pressure (CT-OP) process with adjusting temperature and oxygen partial pressure at the final heat treatment. In this paper, the field-angle dependence of the critical current density was measured at 77.3 K and the crystalline misorientation angle was estimated for four specimens with different critical current densities. It is found that in a parallel magnetic field, the critical current density of the latest Bi-2223 tape of 190 A class is remarkably higher than the other specimens over a wide region of magnetic field. On the other hand, although the critical current density of the latest tape in a normal magnetic field is higher than the other specimens, the difference is relatively small especially at high magnetic fields. Thus, the field-angle anisotropy of the latest tape is higher than the other specimen. The observed results can be explained by the improved condensation energy density and the better c-axis alignment in the latest tape.

Limiting current mechanisms of Bi2223 wires in magnetic fields

Controlled overpressure (CT-OP) processing eliminates pores and heals cracks, whichdensifies the Bi2223 filaments and increases the critical current of Ag-sheathed Bi2223 wire.High current capacity wires with critical current values around 210 A at 77 K and self-fieldhave been achieved. The enhancement of the current capacity seems to be due to reducingthe weak links between Bi2223 grains and improving the flux pinning. In order tounderstand the mechanisms for transport critical current in Bi2223 wires, the dependenceof the critical current on magnetic field and temperature has been investigated. The criticalcurrent is measured as a function of the perpendicular and parallel magnetic fields, up to12 T, at temperatures ranging from 4.2 to 90 K. These results indicate that higher criticalcurrent is associated with highly textured and well connected Bi2223 grains. Tofurther improve a critical current of Bi2223 wires, it is necessary to decrease themisalignment angle and reduce the fraction of Bi2212 and secondary phases.

Development of 3‐in‐one high‐temperature superconducting cable

AbstractA three‐in‐one HTS cable has been developed. Its cable core is composed of a conductor and a shield wound with BSCCO and electrical insulation of the PPLP. The three cable cores are covered in thermal insulated stainless corrugated pipes. The BSCCO wires represent a dramatic innovation by virtue of a newly developed process named Controlled Over‐Pressure (CT‐OP). As a new cable technology, a 350‐m thermal insulation pipe was tested for 7 months to find that the life of the vacuum intensity is more than 10 years. The HTS cable with tension members was designed for installation into an underground duct. In addition, a fault current of 23 kA, 0.63 s, was applied to a sample cable with no damage to the BSCCO wires or the cable insulation. These technologies will be applied to the Albany project in the USA. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(1): 15–24, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20577

Critical current properties in high-temperature superconducting wires and tapes

The hot topics of the critical current properties in YBCO coated conductors and Bi-2223 silver-sheathed tapes are discussed. The dependence of the critical current density in YBCO coated conductors on the superconducting layer thickness is partly associated with the defects nucleated in thicker films and is also caused by the thickness dependent influence of the flux creep. Experimental results on PLD processed conductors with different thicknesses are compared with the theoretical analysis based on the flux creep-flow model. A discussion will also be given for the optimum layer thickness for applications.In Bi-2223 tapes introduction of CT-OP (ConTrolled Over Pressure) process has significantly improved the critical current properties. This progress can be attributed to the improvement of the mean value of the flux pinning strength and the decrease in its distribution width. The possibility of further improvement of the critical current properties is discussed using the flux creep-flow model.

Critical current properties in multifilamentary Bi-2223 tape produced by the over pressure processing

Investigation is done on the effect of ConTrolled Over Pressure (CT-OP) processes on the critical current properties in multifilamentary Bi-2223 tapes. It is found that the critical current density at low magnetic fields is remarkably improved by the new CT-OP process. This result with those on irreversibility field and n-value are compared with the numerical calculation based on the flux creep and flow model. The analysis reveals that the most probable value is increased, although the statistical distribution width is increased for the flux pinning strength. This result indicates that the critical current density at high magnetic fields is deteriorated by the widened distribution. If such an inhomogeneity can be reduced to the level of previous tapes by improving the CT-OP process, the high field performance is shown to be significantly improved.