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Bismuth superconducting wires and their applications
Bismuth superconducting wires and their applications* K. Sato, N. Shibuta, H. Mukai, T. Hikata, M. Ueyama, T. Kato and J. Fujikami Osaka Research Laboratories, Sumitomo Konohana-ku, Osaka, 554, Japan
Electric
Industries
Ltd,
1-1-3
Shimaya,
The combination of a bismuth high Tc phase (Tc = 110 K) and powder-in-tube processing technology enables the fabrication of superconducting wires with high critical current density, mass producibility and flexibility. The maximum critical current density in liquid nitrogen reached 53 700 A c m - 2 in zero magnetic field, 42 300 A c m - 2 at 0.1 T and 12 000 A c m - 2 at 1 T. Jc and Jo-B enhancements were obtained with finely dispersed non-superconducting phases and clean grain boundaries. Various prototypes were made to clarify their feasibility, such as 114 m long wires (Jc = 10 000 A cm 2 at 77.3 K), large current conductors (1~ = 2300 A at 77.3 K), a 0.21 T coil at 77.3 K, a 20.35 T coil at 20.3 K and a 23.37 T coil at 4.2 K.
Keywords: high Tc superconductivity; bismuth wires; critical currents
Since the discovery of new oxide high temperature superconductors in 1986, a large amount of work has been done in this field. There have been reports of an yttrium-based superconductor with a critical temperature, T~, in the region of 90 K, followed by a 110 K T~. bismuth-based superconductor and a 125 K T,. thalliumbased superconductor, thus making it possible to use liquid nitrogen (whose boiling temperature at 1 atm is 77.3 K) as coolant. Not only is liquid nitrogen easy to use and inexpensive, but it also makes it possible to simplify the cryostat and enables a large heat flux. It is expected that the use of a superconductor at the temperature of liquid nitrogen will greatly affect such fields as power generation, power transmission, magnetic energy storage, motors, transportation, medical technology, electronics and many other industries. In terms of energy applications, we need to obtain practical superconducting wires for magnets and conductors. Although there are various processing technologies (a solid-reaction process, liquid process and film process, for example) by which wire can be fabricated, a silver-sheathed wire produced using the solid-reaction process is currently the most promising. Among the many superconductive oxide materials, (Bi,Pb)~ Sr~ Ca~_Cu 30m (high T~ phase) has many advantages, s~uch as a high Tc (110 K), mechanically assisted good alignment and clean grain boundaries. *Paper presented at the conference 'Critical Currents in High Tc Superconductors', 22 24 April 1992, Vienna, Austria
Experimental procedures Silver-sheathed bismuth-based superconducting wires were fabricated in tape form as reported in previous papers ~-3. Multifilamentary wires (61 filaments) were then fabricated using a single-stacking technique. Large current conductors, a rigid conductor and a flexible conductor were fabricated, using a diffusion-bonding technique for the rigid conductor and a multilayer winding technique for the flexible one. Coils were fabricated using a wind and react technique.
Magnetic field dependence of critical current density It is necessary to obtain a critical current density Jc > 10 000 A cm 2 under a magnetic field which will vary according to each application; for example, 0.1 T for a large current conductor and 1 T for magnets. The maximum critical current density of a silver-sheathed bismuth (2223) superconducting wire 4 at 77.3 K is 53 700 A cm 2 in zero magnetic field, 42 300 A cm 2 at 0.1 T and 1 2 0 0 0 A c m -2 at 1 T. At 4 . 2 K 20 K 5'6, the wire shows excellent J c - B properties compared with conventional metallic superconductors. It e x h i b i t s a J c o f 1.03 x 1 0 5 A c m 2 at 4.2 K a n d 2 3 T , and 5.5 x 1 0 " A c m z at 2 0 K and 19.75T. These high Jc values at a super-high field suggest that magnets requiring a feasible field of 23.5 T (1 GHz NMR) are thus made feasible by using bismuth superconducting wires.
0011- 2275/93/030243-04 ,d;, 1993 Butterworth Heinemann Ltd
Cryogenics 1993 Vol 33, No 3
243
Bismuth superconducting wires: K. Sato et al.
Jc (A/cm")
t-
10~
1-10 ~
NbTi/~ 106 10 $~ ~
~ ~
~,.
Ag/BiPbSrCaCuO Wire ,
\ \
"~" " . 2 0 K I10~ x 5.4x104
\ \ 50 \
f
J
\ \100 i ~
~ H (T)
f
Figure 2 Transmission electron micrograph of bismuth-based superconductor inside silver sheath (Jc = 5000 A cm-2)
T -1°°
Figure 1 Critical surface of silver-sheathed bismuth-based superconducting wire measured using transport current technique
Figure 1 shows the critical surface of silver-sheathed bismuth-based superconducting wires, as measured by the transport current technique. This figure shows that these wires could be used over a wider temperature and magnetic field range, compared with wires of metallic superconductors. These improvements were attributed to improvement of the microstructure of the superconductor 4"5 and an increase in the irreversibility lines 7. The microstructure of the superconductor inside the silver sheath, as observed macroscopically by scanning electron micrographs, suggests that the non-superconducting phases, such as (Ca,Sr)2PbO4 and (Ca,Sr)2CuO3, are decreased and dispersed. Microscopically, Figures 2 and 3 show the transmission electron micrographs of superconductors having Jc (77.3 K) values of 5000 A cm -2 (Figure 2) and 45 000 A cm-2 (Figure 3). In the low J¢ specimen, there are non-superconducting phases between the grains, causing weak coupling. In the high J¢ specimen, we did not observe a non-superconducting phase and thus the grains were strongly coupled. We propose a model in which the c-axis transport current component was one of the important factors when considering arc and Jc-B enhancements in the stacked thin-platelet crystals of the high T~ phase of the bismuth-based compound 2's. The connected grain area increases with clean grain boundaries, the current path through these boundaries becomes smooth and the c-axis current component becomes smaller; as a result, the Jc and Jc-B characteristics improve.
244
Cryogenics 1993 Vol 33, No 3
Figure 3
Transmission electron micrograph of bismuth-based superconductor inside silver sheath (Jc = 45 000 A cm --2)
Long wires and flexibility Two long wires (100 m single-core and 114 m 61 filaments) were made and evaluated. The Jc values, defined with a 10 ~3 ~2 m criterion, for the full length of the wires were 6570 A cm-2 for the single-core wire 9 and 9700 A cm -2 for the multifilamentary wire, in zero magnetic field at 77.3 K. These results are summarized in Figure 4. From these results, we can try to obtain longer wires for actual applications 5. In the case of conventional metallic superconductors, it is necessary to construct multifilamentary wires to avoid electromagnetic instability. High temperature superconductors were made into multifilamentary wires to obtain flexibility after sintering. Bending strain characteristics were shown to improve as the number of filaments increased up to 1296. A 0.7% strain (30 mm diameter mandrel) does not reduce the arc of a 1296 filament wire j°. The reason for the good strain resistance of multifilamentary wires is believed to be their ability to prevent the crack initiation and propagation induced in superconductors on bending. Thus, we can make conductors and magnets after sintering. Figure 5 shows the characteristics of the 61 multifilament wire after 150
Bismuth superconducting wires: K. Sato et al.
MERIT
77,3K
PROTOTYPE
CURRENT 'COMPACT LEAD ,LOW COST
-12
"W BUSBAR ,COMPACT ,LARGE CURRENT
O-T31 POWER ,INCREASE CABLE CAPACITY ,COMPACT
lOOm SINGLE-CORE
0-44
I
i0-5
c0,,c I E I
77K MAGNET ,EASY OPERATION
114m 61-FILAMEN
,COMPACT 20~30K ,EASY MAGNET OPERATION (&2K~20~30K)
I
i0 3
q5
10'-
,COMPACT SUPER 'EASY HIGH OPERATION FIELD MAGNET (1.SK~&2K)
4 Relationship bet~veen resistivity and critical current densities for a 100 m single-core wire and a 114 m 61 filament wire Figure
strain cycles (bending 600 times). Thus, a singlestacking multifilamentary wire can exhibit superior bending properties with a lower filament number. These results show that the key issues for practical application of high temperature superconducting wires can be overcome.
Application in large current conductor and magnet Expected applications fall within the six major categories shown in Figure 6, namely: 1, cryogenic
Figure 6 Power applications of silver-sheathed bismuth-based superconducting wire
current leads for metallic superconducting magnets; 2, large current busbars for 77.3 K operation; 3, large current cable conductors for 77.3 K operation; 4, LN2 magnets; 5, medium/low temperature (20-30 K) magnets; and 6, super-high field magnets ( > 2 0 T) for 4.2 K operation. Table 1 summarizes the results of prototypes.
Table
F
I
e =0.18% 120mm cb
m'~ l-u..m_t_ __ ~ =0.48%,,7 =-= 42ram ¢
---- 40 20 __
I
0
5
i
/
100 o-¢ 8O oo 60
Figure
i
,
I
,
T
50 1 O0 Strain Cycles
s =0.31% 70ram ¢ ,
I
1 50
1
Summary of results of prototypes
Application
Current status
Key concept
Current leads
0 . 9 3 W kA 1 1500 A! 0. 5 m
Low He consumption Low silver ratio
Busbar
2 3 0 0 A/1 m Rigid
Very large current Compact
Cable conductor 5 9 0 A / 1 . 4 m Multilayer/spiral wind
Increase capacity Flexibility
LN2 magnet
0.21 T/pancake 180 G/R&W solenoid
Easy operation J c - B enhancement
20-30 K magnet
0 . 3 5 T/pancake (Bex - 20 T)
Easy operation Compact
LHe magnet
1 T/pancake 0.37 T/pancake (Be, = 23 T)
Easy operation Anti-high stress
Bending properties of single-stacked 61 filament wire
Cryogenics 1993 Vol 33, No 3
245
Bismuth superconducting wires: K. Sato et al.
Summary Continuing R & D results from silver-sheathed bismuth (high Tc phase) superconducting wires have suggested that many different fields of application will be feasible in the near future. It is necessary to develop higher Jc values and longer wires to realize these expected applications.
Acknowledgements The authors are grateful to: Drs H. Tuji, T. Ando and T. Isono, JAERI, for joint develoment of a busbar; Drs T. Yamamoto, T. Hara and H. Ishii, Tokyo Electric Power Company, for joint development of a cable conductor; Professor K. Watanabe, H F L S M , Tohoku University, for measuring critical currents at 4.2 K and up to 25 T; and Professor Y. Iwasa, F B N M L , MIT, for measuring critical currents at 4.2 K and 20.3 K with up to 20 T back-up fields.
246
Cryogenics 1993 Vol 33, No 3
References 1 Sato, K., Shibuta, N., Mukai, H., Hikata, T. et M. J Appl Phys
(1991) 70 6484 2 Hikata, T., Ueyama, M., Mukai, H. and Sato, K. Cryogenics
(1990) 30 924 3 Sato, K., Hikata, T., Ueyama, M., Mukai, H. et al. Cryogenics (1991) 31 687 4 Ueyama,M., Hikata, T., Kato, T., and Sato, K. Jpn JAppl Phys (1991) 30 L1384 5 Sato, K., Hikata, T., Mukai, H., Ueyama, M. et M. IEEE Trans Magn (1991) MAG-27 1231 6 Sato, K., Hikata, T. and Iwasa, Y. Appl Phys Len (1990) 57 1928 7 Hikata, T., Sato, K. and Iwasa, Y. Jpn J Appl Phys (1991) 30 L1271 and Physica C (1991) 185/189 2363 8 Sato, K., Hikata, T., Mukai, H., Masuda, T., et al. Adv Superconductivity H: Proc. 1SS'89 (Eds Ishiguro, T. and Kajimura, K.) Springer, Tokyo, Japan (1990) 335 9 Sato, K., Shibuta, N., Mukai, H., Hikata, T. et al. Adv Superconductivity IV: Proc 1SS'91 (Eds Hayakawa, H. and Koshizuka, N.) Springer, Tokyo, Japan (1992) 559 10 Mukai, H., Shibuta, N., Masuda, T., Hikata, T. et al. Adv Superconductivity 111:Proc 1SS'90 (Eds Kajimura, K. and Hayakawa,H.) Springer, Tokyo, Japan (1991) 607
Electric
Industries
Ltd,
1-1-3
Shimaya,
The combination of a bismuth high Tc phase (Tc = 110 K) and powder-in-tube processing technology enables the fabrication of superconducting wires with high critical current density, mass producibility and flexibility. The maximum critical current density in liquid nitrogen reached 53 700 A c m - 2 in zero magnetic field, 42 300 A c m - 2 at 0.1 T and 12 000 A c m - 2 at 1 T. Jc and Jo-B enhancements were obtained with finely dispersed non-superconducting phases and clean grain boundaries. Various prototypes were made to clarify their feasibility, such as 114 m long wires (Jc = 10 000 A cm 2 at 77.3 K), large current conductors (1~ = 2300 A at 77.3 K), a 0.21 T coil at 77.3 K, a 20.35 T coil at 20.3 K and a 23.37 T coil at 4.2 K.
Keywords: high Tc superconductivity; bismuth wires; critical currents
Since the discovery of new oxide high temperature superconductors in 1986, a large amount of work has been done in this field. There have been reports of an yttrium-based superconductor with a critical temperature, T~, in the region of 90 K, followed by a 110 K T~. bismuth-based superconductor and a 125 K T,. thalliumbased superconductor, thus making it possible to use liquid nitrogen (whose boiling temperature at 1 atm is 77.3 K) as coolant. Not only is liquid nitrogen easy to use and inexpensive, but it also makes it possible to simplify the cryostat and enables a large heat flux. It is expected that the use of a superconductor at the temperature of liquid nitrogen will greatly affect such fields as power generation, power transmission, magnetic energy storage, motors, transportation, medical technology, electronics and many other industries. In terms of energy applications, we need to obtain practical superconducting wires for magnets and conductors. Although there are various processing technologies (a solid-reaction process, liquid process and film process, for example) by which wire can be fabricated, a silver-sheathed wire produced using the solid-reaction process is currently the most promising. Among the many superconductive oxide materials, (Bi,Pb)~ Sr~ Ca~_Cu 30m (high T~ phase) has many advantages, s~uch as a high Tc (110 K), mechanically assisted good alignment and clean grain boundaries. *Paper presented at the conference 'Critical Currents in High Tc Superconductors', 22 24 April 1992, Vienna, Austria
Experimental procedures Silver-sheathed bismuth-based superconducting wires were fabricated in tape form as reported in previous papers ~-3. Multifilamentary wires (61 filaments) were then fabricated using a single-stacking technique. Large current conductors, a rigid conductor and a flexible conductor were fabricated, using a diffusion-bonding technique for the rigid conductor and a multilayer winding technique for the flexible one. Coils were fabricated using a wind and react technique.
Magnetic field dependence of critical current density It is necessary to obtain a critical current density Jc > 10 000 A cm 2 under a magnetic field which will vary according to each application; for example, 0.1 T for a large current conductor and 1 T for magnets. The maximum critical current density of a silver-sheathed bismuth (2223) superconducting wire 4 at 77.3 K is 53 700 A cm 2 in zero magnetic field, 42 300 A cm 2 at 0.1 T and 1 2 0 0 0 A c m -2 at 1 T. At 4 . 2 K 20 K 5'6, the wire shows excellent J c - B properties compared with conventional metallic superconductors. It e x h i b i t s a J c o f 1.03 x 1 0 5 A c m 2 at 4.2 K a n d 2 3 T , and 5.5 x 1 0 " A c m z at 2 0 K and 19.75T. These high Jc values at a super-high field suggest that magnets requiring a feasible field of 23.5 T (1 GHz NMR) are thus made feasible by using bismuth superconducting wires.
0011- 2275/93/030243-04 ,d;, 1993 Butterworth Heinemann Ltd
Cryogenics 1993 Vol 33, No 3
243
Bismuth superconducting wires: K. Sato et al.
Jc (A/cm")
t-
10~
1-10 ~
NbTi/~ 106 10 $~ ~
~ ~
~,.
Ag/BiPbSrCaCuO Wire ,
\ \
"~" " . 2 0 K I10~ x 5.4x104
\ \ 50 \
f
J
\ \100 i ~
~ H (T)
f
Figure 2 Transmission electron micrograph of bismuth-based superconductor inside silver sheath (Jc = 5000 A cm-2)
T -1°°
Figure 1 Critical surface of silver-sheathed bismuth-based superconducting wire measured using transport current technique
Figure 1 shows the critical surface of silver-sheathed bismuth-based superconducting wires, as measured by the transport current technique. This figure shows that these wires could be used over a wider temperature and magnetic field range, compared with wires of metallic superconductors. These improvements were attributed to improvement of the microstructure of the superconductor 4"5 and an increase in the irreversibility lines 7. The microstructure of the superconductor inside the silver sheath, as observed macroscopically by scanning electron micrographs, suggests that the non-superconducting phases, such as (Ca,Sr)2PbO4 and (Ca,Sr)2CuO3, are decreased and dispersed. Microscopically, Figures 2 and 3 show the transmission electron micrographs of superconductors having Jc (77.3 K) values of 5000 A cm -2 (Figure 2) and 45 000 A cm-2 (Figure 3). In the low J¢ specimen, there are non-superconducting phases between the grains, causing weak coupling. In the high J¢ specimen, we did not observe a non-superconducting phase and thus the grains were strongly coupled. We propose a model in which the c-axis transport current component was one of the important factors when considering arc and Jc-B enhancements in the stacked thin-platelet crystals of the high T~ phase of the bismuth-based compound 2's. The connected grain area increases with clean grain boundaries, the current path through these boundaries becomes smooth and the c-axis current component becomes smaller; as a result, the Jc and Jc-B characteristics improve.
244
Cryogenics 1993 Vol 33, No 3
Figure 3
Transmission electron micrograph of bismuth-based superconductor inside silver sheath (Jc = 45 000 A cm --2)
Long wires and flexibility Two long wires (100 m single-core and 114 m 61 filaments) were made and evaluated. The Jc values, defined with a 10 ~3 ~2 m criterion, for the full length of the wires were 6570 A cm-2 for the single-core wire 9 and 9700 A cm -2 for the multifilamentary wire, in zero magnetic field at 77.3 K. These results are summarized in Figure 4. From these results, we can try to obtain longer wires for actual applications 5. In the case of conventional metallic superconductors, it is necessary to construct multifilamentary wires to avoid electromagnetic instability. High temperature superconductors were made into multifilamentary wires to obtain flexibility after sintering. Bending strain characteristics were shown to improve as the number of filaments increased up to 1296. A 0.7% strain (30 mm diameter mandrel) does not reduce the arc of a 1296 filament wire j°. The reason for the good strain resistance of multifilamentary wires is believed to be their ability to prevent the crack initiation and propagation induced in superconductors on bending. Thus, we can make conductors and magnets after sintering. Figure 5 shows the characteristics of the 61 multifilament wire after 150
Bismuth superconducting wires: K. Sato et al.
MERIT
77,3K
PROTOTYPE
CURRENT 'COMPACT LEAD ,LOW COST
-12
"W BUSBAR ,COMPACT ,LARGE CURRENT
O-T31 POWER ,INCREASE CABLE CAPACITY ,COMPACT
lOOm SINGLE-CORE
0-44
I
i0-5
c0,,c I E I
77K MAGNET ,EASY OPERATION
114m 61-FILAMEN
,COMPACT 20~30K ,EASY MAGNET OPERATION (&2K~20~30K)
I
i0 3
q5
10'-
,COMPACT SUPER 'EASY HIGH OPERATION FIELD MAGNET (1.SK~&2K)
4 Relationship bet~veen resistivity and critical current densities for a 100 m single-core wire and a 114 m 61 filament wire Figure
strain cycles (bending 600 times). Thus, a singlestacking multifilamentary wire can exhibit superior bending properties with a lower filament number. These results show that the key issues for practical application of high temperature superconducting wires can be overcome.
Application in large current conductor and magnet Expected applications fall within the six major categories shown in Figure 6, namely: 1, cryogenic
Figure 6 Power applications of silver-sheathed bismuth-based superconducting wire
current leads for metallic superconducting magnets; 2, large current busbars for 77.3 K operation; 3, large current cable conductors for 77.3 K operation; 4, LN2 magnets; 5, medium/low temperature (20-30 K) magnets; and 6, super-high field magnets ( > 2 0 T) for 4.2 K operation. Table 1 summarizes the results of prototypes.
Table
F
I
e =0.18% 120mm cb
m'~ l-u..m_t_ __ ~ =0.48%,,7 =-= 42ram ¢
---- 40 20 __
I
0
5
i
/
100 o-¢ 8O oo 60
Figure
i
,
I
,
T
50 1 O0 Strain Cycles
s =0.31% 70ram ¢ ,
I
1 50
1
Summary of results of prototypes
Application
Current status
Key concept
Current leads
0 . 9 3 W kA 1 1500 A! 0. 5 m
Low He consumption Low silver ratio
Busbar
2 3 0 0 A/1 m Rigid
Very large current Compact
Cable conductor 5 9 0 A / 1 . 4 m Multilayer/spiral wind
Increase capacity Flexibility
LN2 magnet
0.21 T/pancake 180 G/R&W solenoid
Easy operation J c - B enhancement
20-30 K magnet
0 . 3 5 T/pancake (Bex - 20 T)
Easy operation Compact
LHe magnet
1 T/pancake 0.37 T/pancake (Be, = 23 T)
Easy operation Anti-high stress
Bending properties of single-stacked 61 filament wire
Cryogenics 1993 Vol 33, No 3
245
Bismuth superconducting wires: K. Sato et al.
Summary Continuing R & D results from silver-sheathed bismuth (high Tc phase) superconducting wires have suggested that many different fields of application will be feasible in the near future. It is necessary to develop higher Jc values and longer wires to realize these expected applications.
Acknowledgements The authors are grateful to: Drs H. Tuji, T. Ando and T. Isono, JAERI, for joint develoment of a busbar; Drs T. Yamamoto, T. Hara and H. Ishii, Tokyo Electric Power Company, for joint development of a cable conductor; Professor K. Watanabe, H F L S M , Tohoku University, for measuring critical currents at 4.2 K and up to 25 T; and Professor Y. Iwasa, F B N M L , MIT, for measuring critical currents at 4.2 K and 20.3 K with up to 20 T back-up fields.
246
Cryogenics 1993 Vol 33, No 3
References 1 Sato, K., Shibuta, N., Mukai, H., Hikata, T. et M. J Appl Phys
(1991) 70 6484 2 Hikata, T., Ueyama, M., Mukai, H. and Sato, K. Cryogenics
(1990) 30 924 3 Sato, K., Hikata, T., Ueyama, M., Mukai, H. et al. Cryogenics (1991) 31 687 4 Ueyama,M., Hikata, T., Kato, T., and Sato, K. Jpn JAppl Phys (1991) 30 L1384 5 Sato, K., Hikata, T., Mukai, H., Ueyama, M. et M. IEEE Trans Magn (1991) MAG-27 1231 6 Sato, K., Hikata, T. and Iwasa, Y. Appl Phys Len (1990) 57 1928 7 Hikata, T., Sato, K. and Iwasa, Y. Jpn J Appl Phys (1991) 30 L1271 and Physica C (1991) 185/189 2363 8 Sato, K., Hikata, T., Mukai, H., Masuda, T., et al. Adv Superconductivity H: Proc. 1SS'89 (Eds Ishiguro, T. and Kajimura, K.) Springer, Tokyo, Japan (1990) 335 9 Sato, K., Shibuta, N., Mukai, H., Hikata, T. et al. Adv Superconductivity IV: Proc 1SS'91 (Eds Hayakawa, H. and Koshizuka, N.) Springer, Tokyo, Japan (1992) 559 10 Mukai, H., Shibuta, N., Masuda, T., Hikata, T. et al. Adv Superconductivity 111:Proc 1SS'90 (Eds Kajimura, K. and Hayakawa,H.) Springer, Tokyo, Japan (1991) 607