WT-19-INV
Progress of Laser Scribing Technology for Multi-filamentary
Structure of HTS Conductors
J. Liu, T. Machi, T. Izumi
(ISTEC-SRL, iSTERA)
Recently, a significant progress on HTS coated conductors (CCs) has been made along with development of
various applications, such as superconducting magnets for magnetic resonance imaging (MRI) and medical
accelerator system in Japan. It is well known, reductions of influence of shielding currents and heat generation due
to temporal and spatial variations of magnetic fields are very important for above applications, and a
multi-filamentary structure of HTS conductors is the most promising method for these purposes. In the past years,
a combination technique of shallow laser irradiation and two-step chemical etching was developed [1]. There were,
however, several problems to be solved, such as delamination and inhomogeneity of Ic values of the filaments.
These issues mainly came from the chemical etching process, for instance, over etching and non-uniformity of
the slot width.
Therefore, we designed and made an RTR laser scribing system using an excimer laser source in the ultra-violet
(UV) region excluding the chemical etching process. No delamination was observed at the edges of the scribed
filaments and the slot was uniform in the width dimension of the longitudinal direction. It was confirmed that
the delamination strength improved to be 60~90MPa by this work from 40~ 60MPa by the previous
combination technique In addition, by optimization of processing conditions, we succeeded in achieving the less
deviation from the average of filament Ic values, about 12%, less than 23% by the previous technique. That was
obtained in the case of 5 mmW EuBCO CC division into 10-filaments, as shown in figure 1. Furthermore, the laser
scribing process window for long CCs was successfully expanded, while there was no superconducting route
between the filaments even for a 60 m long scribed CC, and the hysteresis loss was down to 1/N (N: number of
filaments) as expected.
This work was supported by the Ministry of Economy, Trade and Industry (METI) as “Development of
Fundamental Technologies for HTS Coils” and AMED as “Development of Medical Devices and Systems for
Advanced Medical Services”.
[1] T. Machi, et al., Supercond. Sci. Technol. 26 (2013) 105016
(a) I-V curves for each scribed filament
(b) Normalized Ic distribution for each scribed filament
Fig. 1. Ic distribution of 10-filaments in 5 mmW EuBCO CC measured at 77K (self-field)
WT-20
Multi-filamentary REBCO tapes fabricated by scratching a buffer
layer along the tape longitudinal direction
Chihaya Kurihara, Shinji Fujita, Naonori Nakamura, Mitsunori Igarashi, Yasuhiro Iijima
(Fujikura Ltd.)
For coil application of REBCO tapes which requires accurate magnetic fields such as MRI (Magnetic
Resonance Imaging), we need to divide a REBCO tape into some filaments to reduce the screening current.
Well-known methods for making multi-filamentary tapes are such as etching and slitting a REBCO layer. However,
these may give unexpected damages to a REBCO layer because a REBCO layer is divided directly.
So, we invest a new method by which we slit a buffer layer. We scratch a buffer layer along the tape
longitudinal direction, then get a textured buffer layer and a non-textured buffer layer. After the REBCO process, a
REBCO layer becomes far from well-textured on a non-textured buffer layer. Using non-textured area, we can
make multi-filamentary REBCO tapes without damages to a REBCO layer.
To know the magnetic-field property of our new multi-filamentary tapes, we measured the magnetization of the
tapes. This result shows that we can reduce the magnetization loss. Also, to ensure that our method protects a
REBCO layer, we did a delamination test (Stud-Pull test) and find that our method provides a good mechanical
property. Therefore, we have developed more suitable multi-filamentary REBCO tapes than conventional REBCO
tapes.
WT-21
Transverse Resistance and Current Paths in Low-Loss Striated
HTS Coated Conductors
F. Grilli1,*, R. Gyuraki1, A. Godfrin1, A. Jung1, A. Kario1, R. Nast1, E. Demencik1, W.
Goldacker1
(1Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
Striating HTS coated conductor (CC) tapes into narrow filaments offers the possibility of reducing the tapes’
magnetization losses without unreasonably decreasing their current-carrying capability. However, realizing
well-separated striations presents technological challenges, especially if the number of filaments is large and/or if a
thick layer of metallic stabilizer is present. In these situations, the filaments can be easily coupled and their
effectiveness to reduce magnetization losses strongly diminished or eliminated. While the onset of coupling is well
visible from magnetization loss measurements, the actual path followed by the coupling current is unknown. In this
contribution we present a systematic study of the transverse resistance in HTS CC samples in order to get a deeper
understanding of those paths. In our study, the samples differ in terms of manufacturer (SuperPower and SuperOx),
number of filaments, and presence and thickness of stabilizer material. The stabilizer material is electroplated
before or after laser striation. In addition, oxidation is used as a means to increase the resistance between the
filaments in non-stabilized samples. The results of our measurements are interpreted with a chain network model
and with finite-element simulations. The correlation between the transverse resistance and the measured
magnetization AC losses is pointed out. This work provides useful insights on the factors determining the
transverse resistance in striated HTS CCs, thus indicating ways to improve the effectiveness of the striation process
for AC loss reduction.
WT-22
Relationship between the Strain Effect of Ic and Internal Lattice
Strain in BaHfO3 doped GdBa2Cu3Oy Coated Conductors
T. Usami*,1, Y. Yoshida1, Y. Ichino1, M. Sugano2, S. Machiya3, A. IBI4, T. Izumi4
(1Nagoya Univ., 2KEK, 3Daido Univ., 4ISTEC)
Strain effect of REBa2Cu3Oy (REBCO: RE = Y, Gd, Sm) coated conductors (CCs) is one of the most fundamental
factors for superconducting coil applications. So far, we fabricated GdBCO CCs doped with BaHfO3 (BHO) as
artificial pinning centers by using Reel to Reel systems with Nd:YAG pulsed laser deposition method.
In this study, we carried out bending test and evaluated internal lattice strain by using high intensity X-ray
diffraction at the beam line BL46XU of SPring-8.
Fig. 1 shows Ic at 77 K in self-field as a function of the bending strain. The peak strain (p) of
BHO-doped-GdBCO shifts toward the compressive strain compared with the pure-GdBCO. The value of the
difference between the peak strain of pure-GdBCO (p = -0.33%) and multilayered films consisting of GdBCO
layers and BHO-doped-GdBCO layers (multilayered-GdBCO：p =-0.95%) was 0.62%. In addition, the strain
sensitivity of Ic in the GdBCO CCs which includes BHO becomes smaller.
To clarify difference of the strain sensitivity of Ic each CCs, we measured 2 scan under tensile loading and we
estimate the residual strain from a comparison of the lattice parameters in the CCs with the powder samples.
As a result, the residual strains of pure-GdBCO and multilayered-GdBCO were -0.098% and -0.028%,
respectively. Considering scale of the difference between the peak strain of pure-GdBCO and
multilayered-GdBCO, peak shifts cannot be explained by the residual strains of each CC. The ratio of the
internal lattice strains to the applied tensile strain and more details about the peak strain will be discussed in
presentation.
Acknowledgement
This work was partly supported by a
Grant-in-Aid for Scientific Research
(23226014, 25289358, 15H04252,
15K14301and15K14302). A part of this
work includes the results supported by
the Ministry of Economy, Trade and
Industry (METI) and by the ALCA
project of the Japan Science and
Technology Agency (JST). The
synchrotron radiation experiments were
performed at the BL46XU of SPring-8
with the approval of Japan Synchrotron
Fig. 1 Bending strain dependence of Ic for GdBCO CCs at 77 K in
self-field. The arrows indicate the peak strain for each coated conductors.
Radiation Research Institute (JASRI)
(Proposal No. 2015A1989).