In-field Ic Research Articles

Synergetic evolution of the microscopic crystal orientation and macroscopic superconducting properties of REBCO tape under sever deformation

This study investigates crystal orientation evolution at microscopic level, and changes in the superconducting properties at macroscopic level of rare-earth-barium-copper-oxide (REBCO) superconductor tape under severe deformation. At the microscopic level, in-situ electron backscatter diffraction is used for real-time observation of the crystal orientation evolution during the entire tensile process. At the macroscopic level, the critical current (Ic) value and Ic angle dependence performance are systematically measured under different applied tensile stresses. By comparing the microscopic and macroscopic results, the synergetic evolution mechanism between them is successfully established. Stress at the initial descent point of the Ic value excellently fits the one where the (001)[100] orientation sharply decreases, thereby revealing the real Ic degradation mechanism of REBCO tapes. The application of a moderate applied tensile stress can increase the in-field Ic value and pinning force because new generated defects and strains act as pinning centers. A higher tensile stress can destroy the biaxial texture of the REBCO layer and become a significant barrier to the supercurrent flow. This research elucidates the REBCO degradation mechanism and may assist manufacturers in improving the electromechanical properties of commercial REBCO tape.

A Dynamic-Key Based Secure Scan Architecture for Manufacturing and In-Field IC Testing

The design for testability (DFT) technology based on scan chains is widely used in industry to increase the testability of circuits. However, it also leads to a potential security problem that attackers can use scan chains as a backdoor to attack a system. Common methods to defend such attacks include disabling the scan chain after manufacturing test or employing some secret keys to encrypt/decrypt scan data or to verify the identities of users. The former would make in-field testing impossible and the latter would require storing keys in memory which might also undergo high risk of memory attacks. In this paper we propose a dynamic-key based secure scan architecture that works together with an intrinsic Physical Unclonable Function (PUF) of chips to defend both scan-based and memory attacks while facilitating both manufacturing and in-field testing. A system equipped with this secure architecture will shift out true circuit responses only when legal test patterns are shifted into the scan chains. Moreover, no test key will be stored in memory, hence no memory attacks are possible. We also leverage the PUF to distinct the legal test patterns for different manufactured chips so as to further protect chips. Analysis results show that our protection scheme can achieve a very high security level without sacrificing system performance, testability and diagnosability.

Enhancement of the electromagnetic properties of fully-processed REBCO tapes by high-temperature tensile-creep deformation

We present improvement in the in-field transport critical current (Ic) of Zr-doped RE-Ba-Cu-O (REBCO, RE = rare earth) tapes to remarkable levels by post-deposition tensile-creep deformation at 580 °C. The deformed samples show up to three times higher Ic than a reference sample at 77 K, 1 T when the magnetic field is parallel to the ab-plane. This enhancement in the in-field Ic is attributed to an increase in the density of ab-plane stacking faults that are formed by high-temperature deformation.

Improvement of uniformity of Ic distributions in long REBCO with BMO coated conductors by in-plume PLD method

Long REBa2Cu3OX (REBCO, RE: rare earth element) with BaMO3 (BMO, M: metal) coated conductors have been expected for the industrial and commercial applications at high temperatures in magnetic fields. Especially, the multi-filamentary structure long REBCO with BHO coated conductors are effective for control of the shielding current of coated conductor excited by applied magnetic fields and alternating-current loss. We fabricated long EuBa2Cu3OX (EuBCO) with BaHfO3 (BHO) coated conductors by the IBAD/PLD (conventional PLD) method, which showed the high in-field Ic values. However, in order to realize REBCO with BMO coated conductors for industrial and commercial applications, the much higher uniformity of not only longitudinal and but transversal Ic distributions of long coated conductors with high in-field performance is required. We have tried to develop the long EuBCO with BHO coated conductors by the in-plume (plane-plume) PLD method with high deposition rate of about 24 nm/s to obtain high in-filed performance and low production cost. More recently, we fabricated the 105 m long EuBCO with BHO coated conductors with high uniformity of longitudinal Ic distributions of 2.54 % (STDEV) by the in-plume (plane-plume) PLD method comparing with coated conductors by the conventional PLD method. We measured each Ic value of 8 filaments of 581 µm in width and slot of 20 µm in width for 0.6 m long EuBCO with BHO coated conductors by in-plume (plane-plume) PLD method. Ic distribution in a width direction of the EuBCO with BHO coated conductors by in-plume (plane-plume) PLD method is more uniform than that of the conventional PLD method.

Enhanced low-temperature critical current by reduction of stacking faults in REBCO coated conductors

The effect of stacking faults (SF) on flux pinning and critical current (Ic) in rare earth based coated conductors was investigated. The SF density in YBa2Cu3O7−δ (YBCO) films with and without Dy addition, produced by metal organic deposition, was modified by altering the oxygenation temperature. A detailed microstructural analysis of the coated conductors was performed by x-ray diffraction, scanning and transmission electron microscopy and energy dispersive spectroscopy, and the observed defect population was correlated with both the self-field and in-field Ic. We report that the best self-field Ic was obtained for samples having a low SF density, in spite of the SF being effective flux pinning defects at 77 K for magnetic fields applied within the ab plane. We also show that the SF have no observable flux pinning effect at low temperatures. This study demonstrates that for devices operated at low temperatures, the elimination of SF in the conductor wires is essential to attain higher Ic.

Development of Long Coated Conductors with High In-field Ic Performance by PLD Method at High Production Rate

We fabricated short samples and a 93 m long coated conductor (C. C.) of EuBa2Cu3O7-δ (EuBCO) with BaHfO3 (BHO) by the IBAD and the PLD methods, which exhibited the high in-field minimum Ic value, (Ic(min)), performance of 141.2 (77K in 3 T) and 411.3 (65K in 3 T) A/cm-w for a short sample, and 133.9 (77K in 3 T) A/cm-w for 93 m long C. C. with 3.6μm in thickness, respectively. Moreover, this long EuBCO with BHO coated conductor also showed high uniform longitudinal Ic distributions and n-value in magnetic fields. However, the deposition rate for obtaining the high in-field Ic performance was comparatively slow down to 10μm/h. To realize the low production cost for EuBCO with BHO coated conductors, improvement of the deposition rate of the EuBCO with BHO layer with high Ic is required. To solve this problem, we optimized growth conditions including deposition conditions. One of the objectives of this work was changing the layer growth mode from the vapor-solid (VS) mode to the vapor-liquid-solid (VLS) one to fabricate EuBCO with BHO layers for achievement of high production rate and maintaining the high in-field Ic and Jc performance of the films deposited at slow deposition rates. As a result, we fabricated EuBCO with BHO coated conductors at a high deposition rate of about 40μm/h and production rate of about 10 m/h, which revealed the Ic(min) value of 48.7 A/cm-w at 77K in 3 T for 1.35μm in thickness.

Fabrication of 93.7 m long PLD-EuBCO + BaHfO3 coated conductors with 103 A/cm W at 77 K under 3 T

Introduction of artificial pinning centers such as BaHfO3 (BHO), BaZrO3 (BZO) and BaSnO3 (BSO) into REBa2Cu3O7−δ (REBCO) coated conductor (CC) layers could improve the in-field critical currents (Ic) in wide ranges of temperatures and magnetic fields. In particular, a combination of EuBCO+BHO has been found to be effective for attaining high in-field Ic performance by means of IBAD/PLD process in short length samples. In this work, we have successfully fabricated a 93.7m long EuBCO+BHO CC with 103A/cmW at 77K under a magnet field (B) of 3T applied perpendicular to the CC (B//c). The 93.7m long EuBCO+BHO CC had high uniformity of Ic values and n-values without any trend of fluctuations, independent of the external field up to 0.3T. Ic–B–applied angle (θ) profiles of the 93.7m long EuBCO+BHO CC sample showed the high in-field Ic values in all directions of applied magnetic fields especially B//c (at θ∼180°, Ic=157A/cmW) at 77K under 3T. The profiles were about the same as those in a short length sample.

Progress in Production and Performance of Second Generation (2G) HTS Wire for Practical Applications

Rare earth (RE) based second generation (2G) high temperature superconducting (HTS) wire is an emerging material that has been commercially available to a wide range of energy, scientific, industrial and medical applications including high-field magnets, fault current limiters, motors and generators, transformers, and power cables. High engineering critical current density, high mechanical strength, and high irreversibility field are the major advantages of 2G HTS wires over low temperature superconducting (LTS) wires and bismuth-based first generation (1G) HTS wires. 2G HTS wires with critical current I c (77K, self-field) of 300 ~ 500 A/cm-w and piece lengths of a few hundred meters are being routinely produced. Past and ongoing demonstration projects using the 2G HTS wires suggest that the practical application of this new material is appealing, promising and challenging. Further improvement in wire performance is desired and wire price is to be reduced. In this paper, important properties of 2G wires such as uniformity, in-field Ic and electromechanical behaviors are described. Recent technology advancements in using 2G HTS wire for practical applications are discussed.

Fabrication of Eu1Ba2Cu3O7−δ+BaHfO3 coated conductors with 141 A/cm-w under 3 T at 77 K using the IBAD/PLD process

Introduction of artificial pinning centers such as BaZrO3 (BZO), BaSnO3 (BSO), BaHfO3 (BHO) nano-rods is effective to improve in-field critical currents (Ic). In particular, the BHO doping into Gd1Ba2Cu3O7−δ had been found to exhibit high in-field Ic under wide ranges of temperatures and magnetic fields. Furthermore, a long coated conductor (CC) with high in-field properties and high uniformity was successfully fabricated by means of BHO doping. However, increase of the Ic values exhibited somewhat in a saturated manner with thickening the superconducting films above 3μm. In this work, a new combination of Eu1Ba2Cu3O7−δ (EuBCO)+BHO system was investigated using the IBAD/PLD process to improve in-field performance especially in thick films. As a result, it was found that a EuBCO+BHO film with 3.6μm in thickness showed extremely high property of 141A/cm-w measured at 77K, 3T. This high in-field Ic value was tentatively explained due to suppression of a-axis oriented grains even in thick films. A 200m long EuBCO+BHO CC with 55.5A/cm-w and a 93.7m long CC with 108A/cm-w measured at 77K, 3T were successfully fabricated.

Development of Commercial RE123 Coated Conductors for Practical Applications by IBAD/PLD Approach

Longitudinal homogeneity and REBa2Cu3Ox: RE123 thickness dependence of in-field superconducting properties for commercial RE123 coated conductors (C.C.) were measured at varied temperatures. Self-field Ic homogeneity for typical ∼500-m long samples were evaluated below 2% measured by continues reel-to-reel measurement. In-field Ic distributions were not changed at temperatures from 10K to 77.3K, being estimated by Ic measurements at separated points of a 1km long sample. Linear dependences of in-field Ic on RE123 thickness up to 5μm were observed at temperatures of 20K and 77.3K, in contrast with non-linear dependences observed for self-field Ic for RE123 films. The results indicate good longitudinal homogeneity and universal linearity of thickness dependence for in-field Ic at wide temperature range, which suggest simple scaling for in-field Ic of RE123 wires among different temperatures.

Enhancement of In-Field Current Transport Properties in GdBCO Coated Conductors by $\hbox{BaHfO}_{3}$ Doping

We have investigated the in-field current transport property in BaHfO3 doped GdBa2Cu3O7 - δ coated conductors in a wide range of temperatures and magnetic fields. Significant improvement of in-field critical current Ic was observed, e.g., Ic@77 K, 3 T = 93 A/cm-w, Ic@20nK, 17nT = 700 A/cm-w, which is a comparable value to that of Nb3Sn wire at 4.2 K. Enhancement of the irreversibility field was also observed. These results suggest that BaHfO3 is one of the most promising materials as effective artificial pinning centers and leads to the enhancement of in-field Ic. Furthermore, we have also shown that our analytical expression of electric field versus current density characteristics based on the percolation transition model [1-3] agrees well with the experimental results over a wide range of magnetic fields and temperatures. This analytical expression is useful for the design of superconducting devices because this allows us to predict the current carrying capability of coated conductors not only Jc but also n-value at arbitrary operating conditions of temperature and magnetic field.

$I_{\rm c}$– $B$–$T$ Evaluation for High-$T_{\rm c}$ Superconductors in Pressurized/Depressurized Liquid Nitrogen

Critical current (Ic) and n-values were evaluated for commercially available (Bi, Pb)2Sr2Ca2Cu3O10 (Bi-2223), GdBa2Cu3O7 (GdBCO) and (RE)Ba2Cu3O7 (REBCO, RE = rare earth) superconducting tapes. The transport properties were investigated in magnetic fields up to 1 T in various temperatures around 77 K. The measurements up to the transport current of 500 A were performed in pressurized and depressurized liquid nitrogen using a newly developed apparatus. Bi-2223 showed the largest Ic for magnetic field parallel to the tape surface, whereas it showed the largest anisotropy. It was found that the in-field Ic property of GdBCO was improved. The effect of artificial pinning centers introduced for REBCO was confirmed.

Effect of High BZO Dopant Levels on Performance of 2G-HTS MOCVD Wire at Intermediate and Low Temperatures

Flux pinning in REBCO (rare-earth Ba-Cu-O) by self-assembly of BZO (barium zirconate) nanorods has emerged as one of the most prominent techniques for improving the in-field performance of 2G-HTS wire in terms of Ic and angular Ic anisotropy. In our previous study on metalorganic chemical vapor deposition REBCO wire, an optimum performance was found for 7.5% Zr at 1 T, 77 K, while further increase in Zr content resulted in Ic and Tc degradation. However, recent results indicate that the pinning performance at high Zr content actually surpasses that of the 7.5% Zr wire at intermediate and low temperatures. In-depth understanding of the effect of high Zr levels on REBCO provides a strong potential for further substantial increase in pinning performance at high Zr content if the unwanted effects can be minimized by process modification. In this study, we analyze the effect of high Zr doping levels on REBCO properties with emphasis on microstructure analysis. Structural properties as a function of BZO dopant level have been analyzed using X-ray reciprocal space maps and transmission electron microscopy, while the performance has been characterized using angular in-field Ic characterization up to 9T at temperatures of 20-77 K.

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.

Full Vector Magnetic Field Critical Current Characterization of Coated Conductors Deposited on Solution Deposition Planarized IBAD Templates

Second generation high temperature super-conductor (HTS) wire consists of metal substrate tapes textured with intermediate buffer layers that are coated with a superconducting layer. The applications of these coated conductors require a high current in magnetic fields that are not restricted to a narrow range of angles. Ion beam assisted deposition (IBAD) template tilt, in combination with REBCO vapor deposition, results in asymmetric sample growth. This requires Vector Magnetic Field (VMF) measurement over 180 degrees to be fully described. We have developed a piece wise characterization and analysis method of the VMF using a number of Ic scaling models. Solution Deposition Planarization (SDP) permits REBCO film deposition on 100 nm rms roughness substrates. To test buffer layer effects on film growth, with and without SDP, superconducting films were deposited at Superconductor Technologies, Inc. by co-evaporation of REBCO on IBAD buffer layer templates from Los Alamos. Critical current measurements in VMF up to a magnitude of ~ 0.9 Tesla show behaviors traceable to the effects of buffer layer template on pinning. The ability to discriminate between buffer layers based on in-field Ic behavior is a useful technique for the optimization of buffer layers for future REBCO film deposition.

Current Status of Coated Conductor Development in M-PACC Project

This is a review of the current status of RD degradation, higher in-field Ic, lower AC losses, higher mechanical strength, and higher Je and lower cost. During the three-year development, the interim targets were almost satisfied and the activities performed were at the top technical level in the world. We are now in the final stages of development, aiming to achieve the final targets, which are based on the specifications for marketing the cables, transformers and SMES.

Measurement of HbA 1c by pharmacia FPLC: An inter-hospital comparison

For most applications of high-temperature superconducting tapes, a high critical current (Ic) and critical current density (Jc) under a magnetic field are both required. The simplest way to achieve high Ic is to increase the thickness of the superconducting layer. However, doing so also reduces Jc, which is called the thickness effect. In this work, to inhibit the thickness effect, a series of Y0.5Gd0.5Ba2Cu3O7-σ (YGBCO) films with different thicknesses (240–1200 nm) were deposited by multi-step pulsed laser deposition on cerium oxide (CeO2) buffered substrates. The thickness dependence of the in-field Jc was systematically investigated. The in-field Ic at 77 K and 0–0.5 T was measured using the four-probe method, the surface morphology was observed using scanning electron microscopy, the structure and texture were measured using X-ray diffraction, and the internal residual stress was evaluated using the Williamson–Hall method. It was found that Jc first increased and then decreased with increasing YGBCO film thickness. The 480-nm YGBCO film had the highest Jc of 4.33 MA/cm2 at 77 K and a self-field>1.5 MA/cm2 under a magnetic field of 0.5 T. A 720-nm YGBCO film showed the slowest rate of Jc degradation under a magnetic field. The experimental results are discussed by considering the deposition process and growth model.