Masaya Konishi

Development of RE123 coated conductor by ISD method

Abstract High rate deposition of HoBa2Cu3O7−δ (HoBCO) layers using the pulsed laser deposition method were experimented for long high temperature superconducting (HTS) coated conductor. Laser conditions and oxygen ambient during HoBCO deposition were precisely inspected. This revealed that the deposition rate of HoBCO reached to 5 μm/min. Even at such high deposition rate, the Jc of HoBCO films remained over 105 A/cm2 on the biaxial buffered substrate fabricated by the inclined substrate deposition (ISD) method. Moreover continuous tape production equipments were installed to make a long and flexible coated conductor by ISD method. These equipments will enable us to fabricate of over 100 m long coated conductor. 55 m long coated conductor were fabricated by using these equipments as our first trial of long length fabrication. Evaluation of Jc distributions of 55 m coated conductor revealed that all parts of 1 m in the 55 m conductor had the Jc over 104 A/cm2.

Nondestructive Diagnostics of Narrow Coated Conductors for Electric Power Applications

We have succeeded in characterizing local critical currents and electromagnetically equivalent widths of slit coated conductors (CCs) as a function of their longitudinal position based on reel-to-reel scanning Hall-probe microscopy (RTR-SHPM). The aim is to make a quality control of slit CCs intended for electric power application, such as electric power cable in particular, for ac losses reduction. Long pieces of slit CCs, i.e., collectively 40-m-long pieces of 2-mm-wide slit CCs, were transferred in their longitudinal direction, and continuously magnetized in a liquid nitrogen bath; the magnetic field distributions of the samples were then measured by scanning a Hall sensor. From the magnetic field distributions, we could evaluate local critical currents and the equivalent widths of the slit CCs as a function of their longitudinal position. The difference between the equivalent width and the geometrical width of a CC corresponds to the damage due to the slitting process. This means that we can discuss such damage precisely together with its statistics along the longitudinal direction. This kind of diagnostics will be a very powerful technique for establishing slitting processes for producing narrow CCs for overcoming the issue of ac losses for electric power application comprising CCs.

Fabrication of Josephson Junction on (001) YBa2Cu3Ox Single Crystal Substrate.

We have fabricated a junction consisting of an a-axis oriented film and a (001) substrate of YBa2Cu3Ox . First, a multi-layer structure has been prepared by film deposition at rather low substrate temperature, and the junction with an area of 40×40 µ m2 has been fabricated by conventional photolithography and etching technique. This junction exhibits supercurrent below 65 K and Shapiro-steps under microwave irradiation at 5 GHz. This Josephson junction is the first one formed on the high-T c single crystal substrate, which has high possibility of improvement in reproducibility due to the high quality electrodes.

Homoepitaxial growth of YBCO thin films an YBCO single crystals

YBCO films were grown on [001] YBCO single crystal substrates using the off-axis RF magnetron sputtering method. The interface between the substrate and the film was observed using TEM. The crystal orientation of the film was found to be dependent on the growth temperature. C-axis oriented films with smooth interfaces and holes on their surfaces were obtained at 760/spl deg/C. A-axis oriented films grown at 580/spl deg/C had smooth surfaces, but the interface was rather poor. Lattice mismatches occurred at the interface due to deoxidization and oxidization of the substrate during the film growth-process.<<ETX>>

Lateral Distribution of Critical Current Density in Coated Conductors Slit by Different Cutting Methods

We have investigated the lateral distributions of critical current densities in narrow coated conductors slit by different cutting methods. The objective was to find an optimal slitting process to make a narrow conductor that should be effective for ac loss reduction of assembled conductors such as power transmission cables. In-plane 2-D distribution of critical current density was characterized by means of scanning Hall-probe microscopy. From an analysis along the width direction, we could estimate the degradation in critical current density by a slitting process at both tape edges. We determined an equivalent width for the slit tapes in order to discuss such degradation with a high spatial resolution. Furthermore, the 2-D scanning allows us to evaluate the effective tape width as a function of longitudinal coordinate. In other words, we could evaluate the equivalent width of a slit conductor together with its statistics along the longitudinal direction. As a result, it was found that coated conductors slit by laser cutting processes were clearly better than those by mechanical ones from the viewpoint of less degradation at their edges. In addition, an optimal condition among laser slitting processes was also presented.

Fabrication of

We have been fabricating Gd1Ba2Cu3Ox (GdBCO) coated conductors (CCs) on textured clad-type substrates by using pulsed laser deposition (PLD) method for high temperature superconducting (HTS) power cables. In this project, numerous numbers of CCs are required for fabricating a 66 kV class, 3-in-One HTS cable and for the evaluation of its properties. In order to achieve this, it is important to ensure the stable production and the high-throughput manufacturing. In this work, we have newly installed a high power laser of 300 W for the PLD equipment, which has 1.66 times higher power than the previous one. As a result, the stability of manufacturing and the production rate were greatly improved. In addition, we have adopted a wide tape approach using 30 mm width substrates to increase the throughput. Moreover, we have optimized deposition condition for a seed layer by electron beam (EB) evaporation method, then the maximum Ic value for a short sample has achieved 497 A/cm at 77 K in the self-field. With this improved process, long GdBCO tapes with high Ic have been successfully fabricated.

{\rm Gd}_{1}{\rm Ba}_{2}{\rm Cu}_{3}{\rm O}_{\rm x}

We have been developing long coated conductors with high critical current, Ic, by multi-plume and multi-turn pulsed laser deposition (MPMT-PLD) method. In addition to YBa2Cu3O7-X (YBCO) coated conductors, we have recently succeeded in fabricating long GdBa2Cu3O7-X (GdBCO) coated conductors. The 30 m long and 60 m long GdBCO conductors showed higher Jc values in a magnetic field and lower anisotropy than the conventional long YBCO conductor. Critical current, Ic, of the GdBCO at 3 T and 77 K was more than 20 A, which was three times larger than that of the YBCO long coated conductor. To demonstrate the high performance of GdBCO, we fabricated GdBCO coils and compared it with the YBCO coil. The GdBCO coil was successfully energized up to large Ics of 74.2 A and 184.8 A at 77 K and 64 K, which generated magnetic field of 0.5 T and 1.2 T at 64 K and 77 K. We confirmed that the GdBCO conductor is more promising than the YBCO conductor for the application because its superior transport properties in a magnetic field.

Coated Conductors for HTS Cables

As a fundamental development of RE-123 cable conductor, the electromagnetic and mechanical properties of multi-layer spiral cable conductors using HoBCO thin film tapes were studied. The critical current of the HoBCO tape shows 95% performance at the 180 MPa tensile stress. Self magnetic field simulation of a 4-layer spiral cable conductor was carried out. AC loss calculation of the conductor with current capacity of 3 kA was also performed. The AC loss was calculated less than 0.5 W/m, which shows the possibility of low AC loss of HoBCO cable conductor. In the calculation, it was found that the gap between thin film tapes in the cable conductor makes an important role in reducing AC losses. Based on these design studies, fabrication of model cable conductor was performed. Several kinds of 1 m multi-layer spiral conductors and a 7 m 4-layer spiral conductor were made by using HoBCO tape and dummy tape. The stranding machine was especially applied to the 7 m 4-layer dummy cable conductor.

GdBaCuO and YBaCuO Long Coated Conductors by IBAD-PLD Method—Enhancement of Production Speed and Critical Current in a Magnetic Field

In order to fabricate YBa2Cu3O7−x (YBCO) coated conductors with high critical current density Jc in magnetic fields, we fabricated YBCO coated conductors with artificial pinning centers by the pulsed laser deposition (PLD) method on a self epitaxial PLD‐CeO2 layer and ion‐beam assisted deposition (IBAD)‐Gd2Zr2O7 (GZO) buffered Hastelloy tape. Artificial pinning centers were introduced by the PLD deposition using the yttria‐stabilized zirconia (YSZ) oxide target (nano‐dot method) and YBCO target including YSZ particles (mixed target method). In the experiments using YSZ oxide target, YSZ nano‐dots were observed. They were approximately 15 nm in height and 10 nm to 70 nm in diameter. We found that the density of nano‐dots was controlled by the number of laser pulses. These samples exhibited higher Jc than YBCO films in magnetic fields. Furthermore, a similar improvement of Jc was observed in the experiments using YBCO target including YSZ particles. TEM observation revealed that columnar nano‐structure made...

Design study of model cable conductor by using HoBCO thin film tape

In SRL‐Nagoya Coated Conductor Center (NCCC), long buffered substrate tapes and YBCO coated conductors have been successfully fabricated by using ion‐beam assisted deposition (IBAD) and pulsed laser deposition (PLD) methods. For the buffered tape, the PLD‐CeO2 method, what we call the “Self‐Epitaxial” method, realized the high degree of in‐plane texturing around 4 degrees along the length of 220 m. For YBCO deposition, we have recently introduced new reel‐to‐reel PLD equipment with a multi‐plume and multi‐turn deposition system (MPMT PLD). This system succeeded in fabricating a long coated conductor with a high critical current, Ic, of 245 A and length of 212 m. Ic ×L (length) reached the world record of 51940 Am. Furthermore, the introduction of artificial pinning center and RE 123 materials were also studied for improving flux pinning and enhancing Ic. A new columnar structure of the “bamboo structure” (BaZrO3/Y123 layer‐stacked structure) was found in Y123+YSZ sample. This columnar structure and the st...