Shuji Hahakura

Development of in-plane aligned YBCO tapes fabricated by inclined substrate deposition

Abstract High temperature superconducting thin film tapes, which consist of a flexible metal substrate, buffer layer, and Y 1 Ba 2 Cu 3 O x (YBCO) layer have been developed for power application. Ni-alloy tape was used as the substrate. Both the YBCO layer and the buffer layer were formed by pulsed laser deposition (PLD) because of an advantageous of high deposition rate. Inclined substrate deposition (ISD) was developed to introduce in-plane alignment for the buffer layer on the non-textured metal substrate. YBCO films epitaxially deposited on the ISD buffer layer by normal PLD had high J c values over 10 5 A/cm 2 at 77 K. For verification of high rate productivity of the PLD/ISD method, we demonstrated high rate deposition of the yttria stabilized zirconia buffer layer and YBCO superconducting layer. We also performed continuous deposition of over 10 m YBCO thin film tapes with a reel-to-reel substrate transfer system combined with 200 W high power laser equipment.

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.

High-Ic HoBCO coated conductors by PLD method

Ho/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/ (HoBCO) coated conductors by using Pulsed Laser Deposition (PLD) have been developed on textured Ni-alloy substrates. Hetero-epitaxial growth of CeO/sub 2//YSZ/CeO/sub 2/ was developed to introduce in-plane alignment for buffer layers. CeO/sub 2/ seed and cap layers were deposited by RF sputtering. YSZ diffusion layer was deposited by PLD. The most advantage of buffer layers are high growth rate and large deposition area by using in-plane alignment of textured substrate. This was demonstrated by a high production speed of buffer layers. CeO/sub 2/ and YSZ buffer layers show a high production speed of 7 m/h and 8 m/h, respectively. As for the HoBCO deposition, a production speed of 10 m/h was demonstrated by using high growth rate of 4 /spl mu/m/min in our PLD process. Ic of the short sample reached 357 A/cm-width at 77 K, 0 T, and 2,423 A/cm-width at 30 T, 4.2 K. Long length HoBCO conductors up to 35 m were performed by using reel to reel tape transfer system of each process.

Development of YBa/sub 2/Cu/sub 3/O/sub y/ tape by using inclined substrate method

YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) wire has higher critical current density (J/sub c/) and less degradation in J/sub c/ upon application of a magnetic field than (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ (Bi2223) powder-in-tube wire. It has good potential for use as a high temperature superconducting (HTS) wire following Bi2223. For many years, we have been studying a process to form biaxially aligned YBCO film on metal-based tape by the inclined substrate deposition (ISD). To date, we have succeeded in fabricating a 6 m-long YBCO wire by a continuous process of the ISD method. We have also investigated performance of the fabricated YBCO wire and the advantages of YBCO wire in its applications to rectifier-type fault current limiter (FCL) and HTS cable.

Development of 200 meter HoBCO Coated Conductors on Ni-Alloy Textured Substrates

(Ho1Ba2Cu3Ox) (HoBCO) coated conductors on textured Ni-alloy substrates were developed by using pulsed laser deposition (PLD). Hetero-epitaxial growth of CeO2/YSZ/CeO2 was used to introduce in-plane alignment for buffer layers. CeO2 seed and cap layers were deposited by RF sputtering. YSZ diffusion layer was deposited by PLD. The most advantage of these buffer layers are high growth rate and large deposition area by using textured substrate. As for the HoBCO deposition, a production speed of 20 m/h with growth rate of 2-3 mum per minute was demonstrated in our PLD process. By optimizing the deposition temperature, lc and Jc of the short samples reached 265 A/cm-width and 5.6 MA/cm2 at 77 K, 0 T, respectively. Long length HoBCO conductors over 200 m were performed by using reel to reel tape transfer system of each process.

Dependence of transport current losses in coated conductors on magnetic property of substrate

Influence of ferromagnetism of the substrates on transport current losses in HoBaCuO-123 tape-shaped coated conductors with ferromagnetic Ni-alloy substrates was investigated by measuring the losses as a function of an external DC magnetic field. The losses were measured by electric and calorimetric methods simultaneously to prove the validity of the measured data. The experimental results showed significant influence of ferromagnetism of the substrates, when the substrates were not magnetically saturated by an external DC magnetic field. On the other hand, when the substrates were saturated, the loss characteristics were less influenced.

Thin Film YBCO Tape with Over 3 meter Length Fabricated by Inclined Substrate Deposition

We have employed the inclined substrate deposition (ISD) method in order to get a biaxially textured YBCO film [1,2]. For verification of high producibility of ISD method, we have been trying to fabricate YBCO tapes with several meter lengths using the Reel-to-Reel continuous deposition system. The X-ray pole figure measurement revealed that ISD buffer layers and YBCO layers on them were in-plane aligned over 3 meter long. The YBCO tape had the high Jc value of more than 104 A/cm2 at 77.3K over 3 meter length.

Recent progress of HTS magnet using Bi-2223 Ag-sheathed wire

The authors have succeeded in developing two types of refrigerator cooled high-Tc superconducting magnets-a high magnetic field type and a large bore type. The high magnetic field type has a room temperature bore of 50 mm, an inner diameter of 80 mm and an outer diameter of 300 mm. The coil height is 200 mm, using 24 double pancakes. The magnet generated 7.1 T over 24 hours and was excited at a rate of 7 T/minute. This high ramp rate was ten times faster than that of a refrigerator cooled magnet using metallic superconducting wires. The large bore type magnet has a room temperature bore of 280 mm, an inner diameter of 400 mm and an outer diameter of 520 mm. The coil height is 18 mm using 2 double pancakes. The magnet generated 0.17 T and was excited at a rate of 0.034 T/s. These two types of HTS magnets, produced by using only Bi-2223 Ag-sheathed tapes, have been continuously operated at 20 K for practical applications.

Development of Ag-sheathed Bi2223 superconducting wires and their application to magnets

Silver-sheathed BiPbSrCaCuO 2223 superconducting wires with long length and high Jc of over 10/sup 4/ A/cm/sup 2/ were developed by using the powder-in-tube method. Future possibilities to obtain much higher Jcs are discussed in relation to crystal alignment, connectivity between grains and flux pinning. High amperage wires and high strength wires were also developed for large scale magnet application. High I/sub c/ of over 300 A at 77 K were obtained for the wire with large cross sectional area. Good stress and strain tolerant characteristics were also obtained for silver alloy sheathed wires. In order to apply the HTS wires for AC use, it is necessary to reduce AC loss. So, the AC loss of the wires are also discussed. As a progress of wire technology, we have fabricated many types of magnets, such as pancake magnets and solenoidal magnets. In the case of 77 K application, it is promising to apply for AC use because of large heat capacity of HTS wires and liquid nitrogen. So, we are developing the 500 kVA transformer and pulse magnet for SMES. A refrigerator cooled magnet operated near 20K was fabricated. This magnet was operated at 21 K and generated 3 T inside a /spl phi/40 mm room temperature bore, stably generated 2.5 T continuously for over 150 hours and could be operated at high ramp rate of over 12 T/min. As for the 4.2 K operation, high field insert magnet for 1 GHz NMR application are developed. Highest magnetic field of 24 T was achieved using the hybrid magnet at MIT and persistent current mode operation was done by using the layer wound coil with persistent current switch.

Development of HoBCO Coated Conductors by Fluorine-Free MOD/PLD Composite Process

Ho1Ba2Cu3Ox (HoBCO) coated conductors by using a fluorine-free metal organic deposition (MOD)/PLD composite process has been developed. Excellent epitaxial growth of MOD-HoBCO layers on PLD-HoBCO layers were confirmed on buffered metallic Ni-alloy textured substrates. The FWHM of MOD-HoBCO layers were typically 6.5-7 degrees. Jc over 1 MA/cm2 at 77 K, 0 T was confirmed when MDO-HoBCO thickness was less than 1 mum. By using continuous reel to reel equipments with coating, heating and firing process, several conductors with HoBCO thickness over 1 mum were obtained. A long length HoBCO coated conductor up to 100 m length was fabricated.