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Strain effects on the AC critical current of Bi-2223 superconducting tapes
Physica C 386 (2003) 154–157 www.elsevier.com/locate/physc
Strain effects on the AC critical current of Bi-2223 superconducting tapes Zhaoyang Lu a,*, Xuqiang Huang a, Yanfa He b, Jinghui Li b, Jing Sun b, Yinan Wang b, Xihua Zong b, Jinxing Wang b, Chengshan Li c, Pingxiang Zhang c, Yong Feng c, Lian Zhou c a
School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110004, PR China b Department of Physics, Northeastern University, Shenyang 110004, PR China c Northwest Institute for Nonferrous Metal Research, XiÕan 710016, PR China
Abstract Axial tensile strains effects on the AC critical current of Bi-2223/Ag and Bi-2223/AgMn tapes produced by the powder-in-tube method have been studied, at 77 K. 5 lV/cm field criterion was used to determine the AC and DC critical current. The degradation of AC critical current due to axial tensile strain is irreversible, the normalized AC and DC critical current Icn vs tensile strain e curves Icn ðeÞ of Ag and AgMn/Ag sheathed Bi-2223 superconducting composite tapes are almost the same when the axial tensile strain is less than e0:9 , when the axial tensile strain is larger than e0:9 , the AC critical current Icn decrease less rapidly than DC critical current Icn , and at the same strain, the normalized AC critical current is greater than normalized DC critical current. This may be due to the greater relative increment in DC voltage than in AC voltage when the strain is large enough to deteriorate the transport capacity of the tape. The AC and DC Icn ðeÞ curves have the same empirical formula as Icn ¼ 1 ðe=aÞb , where a and b are constants. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.25.Ld; 74.25.Fy; 74.72.Hs; 74.60.Jg Keywords: Axial tensile; AC critical current; Strain effects; Bi-2223
1. Introduction Applications, such as superconducting transformer and magnet, require that BSCCO tapes have good mechanical performances, in addition
*
Corresponding author. Tel.: +86-2483682222; fax: +862423915211. E-mail address: [email protected] (Z. Lu).
to current transport capacity, to resist the heat stress and hoop stress. Therefore, it is important to study the effects of strains on the AC critical current of the Bi-based tapes. Several studies have examined the tensile strain effects on the DC critical current of Bi-based superconducting tapes or wires [1–15], but no papers on the strain effects on the AC critical current of Bi-based superconducting tapes or wires. This paper explores the axial tensile strain effects on the AC critical current of Bi-2223 superconducting tapes.
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02243-8
Z. Lu et al. / Physica C 386 (2003) 154–157 Table 1 Details of the specimens No.
Ag19
AgMn61
Matrix Filaments Dimension (mm2 ) Ic (A) DC Ic (A) AC
Ag 19 3:86 0:28 13.0 10.0
Ag–0.5%Mn 37 4:12 0:28 25.7 20
155
terion was selected to determine the AC critical current. The AC voltage includes the superconducting voltage and induction voltage, induction voltage is influenced by the voltage contact points [19]. In this paper, the voltage contact points were soldered at the face center of the tape, and the area enclosed by the signal wires was minimized. DC critical current was measured by a standard fourprobe method, a 5 lV/cm field criterion was also selected to determine the critical current.
2. Experimental The Bi-2223/Ag and Bi-2223/AgMn superconducting tapes were fabricated by the powder-intube method [16]. Details of the specimens are listed in Table 1. The critical current listed in Table 1 were determined by a 5 lV/cm field criterion. Two samples of Ag19 and AgMn61 were tested. For axial strains vs critical current measurements, a new facility of 300–2000 N capacity driven by a servo-motor was fabricated [17]. The specimen is soldered between two stainless-steel rods, one of them being movable. The stress is applied to the specimen by the movable rod connected to a dynamometer. A displacement linear voltage differential transformer (LVDT) is used to monitor the sample elongation. Gauge length of 20–25 mm was used for all tests and was defined as the distance between the ends of the stainless-steel rods. Strain is calculated as e ¼ D=L0 , where L0 is the initial gauge length and D is the displacement measured by LVDT. The specimen was cooled slowly in liquid nitrogen to avoid tensile preloads from thermal contraction. Stepped-loading procedure was used to slowly apply increasing strain at an increment of 0.02–0.05% to allow simultaneous measurement of both AC critical current and DC critical current. When a given strain was obtained, DC critical current was measured before and after measuring an AC critical current curve in the same condition and environment and the same piece of sample, respectively. For AC critical current measurements, a standard four-probe arrangement with voltage taps separation of 10 mm was used to get the voltage and phase h by locking-in technique, used to measure AC loss of superconductor [18], at a given AC current of 50 Hz, a 5 lV/cm field cri-
3. Experimental results and analysis The measured AC and DC V –I curves are shown in Fig. 1. The AC voltage is higher than DC voltage, and the voltage contact points have influence on the AC voltage. In order to determine the AC critical current, the production of measured AC voltage by the cosine of the phase h was used as AC voltage. A 5 lV/cm field criterion was used to determine the AC and DC critical current, as shown in Fig. 1. The AC critical current determined by 1 lV/cm field criteria is too small compared with the DC critical current, and the tape is still at superconducting state transporting AC current. If 10 lV/cm field criterion was adopted, the superconductor–normal conductor transfer has already been finished. The axial tensile strain e vs normalized AC and DC critical current Icn curves Icn ðeÞ at 77 K for
Fig. 1. The AC and DC V –I curves and criteria for determining the AC and DC critical current.
156
Z. Lu et al. / Physica C 386 (2003) 154–157
Fig. 2. The axial tensile strain dependence of AC and DC critical current of 19-filament Bi-2223/Ag superconducting tapes.
Fig. 3. The axial tensile strain dependence of AC and DC critical current of 61-filament Bi-2223/AgMn superconducting tapes.
specimens Ag19 and AgMn61 are shown in Figs. 2 and 3, respectively. The normalized critical current Icn equals Ic =Ic0 , where Ic0 is the zero-strain Ic value. The AC Icn ðeÞ curves of Ag19 and AgMn61 are of the same shape of that of DC Icn ðeÞ curves. The AC critical current Icn remains constant when the strain is small, and decreases slowly as the strain increases. The critical current Icn begins rapid irreversible degradation when the strain is up to a limit, which is written as e0:9 , denoting the strain value when the normalized critical current is 0.9. The e0:9 value of samples Ag19A and AgMn61 are 0.32%, and 0.34%, respectively.
When the strain is greater than e0:9 the normalized AC critical current is greater than normalized DC critical current. In another word, the e0:9 of the AC critical current is greater than that of DC critical current. The normalized AC critical current of Ag19 is 0.67 at e ¼ 0:42%, while the DC Icn is 0.58. The characteristic that AC critical current can endure greater strain and the normalized AC critical current is greater than DC Icn makes it possible to adopt e0:9 of DC critical current instead of that of AC critical current as the criteria for application superconductor design, because it is easy to measure e0:9 of DC critical current. The AC critical current Icn vs tensile strain e curves Icn ðeÞ of Ag19 and AgMn61 can also be described by the formula as [17,20]: e b Icn ¼ 1 ð1Þ a where the a and b are constants, a, the strain value when the critical current becomes zero, equals 0.0048 (0.48%), and 0.0044 (0.44%) for specimens Ag19 and AgMn61, respectively, b equals 6.37 and 6.75 for specimens Ag19, and AgMn61, respectively. Eq. (1) fits well the Icn ðeÞ curves of Ag19 and AgMn61, as shown by the open symbols in Fig. 4. Why AC critical current can endure larger strain? One explanation is related to the different transport mechanism of AC and DC superconducting current. Another explanation is as follows: the DC voltage VDC ¼ Vsc þ Vsh , the AC voltage VAC ¼ Vsc þ Vsh þ Vi , where Vsc , Vsh and Vi is the
Fig. 4. The measured and fitted AC Icn ðeÞ curves of Ag19 and AgMn61 superconducting tapes.
Z. Lu et al. / Physica C 386 (2003) 154–157
voltage of the superconductor, the sheath materials and induced voltage, VAC > VDC as shown in Fig. 1. The induction voltage depends on the whole current transporting the tapes. When strain is large enough to deteriorate the transport capacity of superconducting tapes, more current flows in the sheath, the DC voltage VDC increase, and the AC voltage VAC increase either, but less in relative amplitude, this has been proved by the AC and DC V –I curves when the strain is greater than the irreversible strain limits e0:9 [17], the DC critical current decreases greater in relative amplitude than AC critical current, so the normalized AC critical current is greater than DC Icn determined by the same field criteria at the same strain.
4. Conclusions 5 lV/cm field criteria can be used to determine the AC and DC critical current. The AC and DC Icn ðeÞ of Ag and AgMn/Ag sheathed Bi-2223 superconducting composite tapes are almost the same when the axial tensile strain is less than e0:9 , when the axial tensile strain is larger than e0:9 , the AC critical current decrease less rapidly than DC critical current, and at the same strain, the normalized AC critical current is greater than normalized DC critical current. This may be resulted from the greater relative increasement in DC voltage than that in AC voltage when the strain is large enough to deteriorate the transport capacity of the tape. The AC Icn ðeÞ curves have the empirb ical formula as Icn ¼ 1 ðe=aÞ , where a and b are constants.
157
Acknowledgements This paper was supported by National Natural Science Foundation of China (granted no. 19474010), and by the National Center for R&D on Superconductivity of China (granted no. 863CD010104), and by the Chinese Foundation of Doctoral Education (granted no. 96014516). References [1] J. Schwartz, H. Sekine, et al., IEEE Trans. Magn. 27 (1991) 1247. [2] H. Sekine, J. Schwartz, et al., J. Appl. Phys. 70 (1991) 1596. [3] J.W. Ekin et al., Appl. Phys. Lett. 61 (1992) 858. [4] L. Gherardi et al., Cryogenics 34 (1994) 781. [5] R. Wesche et al., Cryogenics 36 (1996) 419. [6] B. ten Haken et al., IEEE Trans. Appl. Supercond. 5 (1995) 1298. [7] B. ten Haken et al., IEEE Trans. Magn. 32 (1996) 2720. [8] B. ten Haken et al., IEEE Trans. Appl. Supercond. 7 (1997) 2034. [9] Y.K. Huang, B. ten Haken, et al., IEEE Trans. Appl. Supercond. 9 (1999) 2702. [10] W. Goldacker et al., IEEE Trans. Appl. Supercond. 5 (1995) 1835. [11] K. Katagiri et al., Cryogenics 36 (1996) 491. [12] K. Katagiri et al., Cryogenics 38 (1998) 283. [13] K. Katagiri et al., Cryogenics 39 (1999) 453. [14] B. Ullmann et al., IEEE Trans. Appl. Supercond. (1997) 2042. [15] Z. Lu et al., Physica C 337 (2000) 150. [16] C.S. Li et al., Physica C 282–287 (1997) 2611. [17] Z. Lu, Stress and strain effects on the critical current of Bibased superconducting tapes, Ph.D. thesis, Northeastern University, Shenyang, PRC, 2001. [18] J. Li et al., Physica C, these Proceedings. [19] M. Ciszek et al., Physica C 233 (1994) 203. [20] Z. Lu et al., Physica C, these Proceedings.
Strain effects on the AC critical current of Bi-2223 superconducting tapes Zhaoyang Lu a,*, Xuqiang Huang a, Yanfa He b, Jinghui Li b, Jing Sun b, Yinan Wang b, Xihua Zong b, Jinxing Wang b, Chengshan Li c, Pingxiang Zhang c, Yong Feng c, Lian Zhou c a
School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110004, PR China b Department of Physics, Northeastern University, Shenyang 110004, PR China c Northwest Institute for Nonferrous Metal Research, XiÕan 710016, PR China
Abstract Axial tensile strains effects on the AC critical current of Bi-2223/Ag and Bi-2223/AgMn tapes produced by the powder-in-tube method have been studied, at 77 K. 5 lV/cm field criterion was used to determine the AC and DC critical current. The degradation of AC critical current due to axial tensile strain is irreversible, the normalized AC and DC critical current Icn vs tensile strain e curves Icn ðeÞ of Ag and AgMn/Ag sheathed Bi-2223 superconducting composite tapes are almost the same when the axial tensile strain is less than e0:9 , when the axial tensile strain is larger than e0:9 , the AC critical current Icn decrease less rapidly than DC critical current Icn , and at the same strain, the normalized AC critical current is greater than normalized DC critical current. This may be due to the greater relative increment in DC voltage than in AC voltage when the strain is large enough to deteriorate the transport capacity of the tape. The AC and DC Icn ðeÞ curves have the same empirical formula as Icn ¼ 1 ðe=aÞb , where a and b are constants. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.25.Ld; 74.25.Fy; 74.72.Hs; 74.60.Jg Keywords: Axial tensile; AC critical current; Strain effects; Bi-2223
1. Introduction Applications, such as superconducting transformer and magnet, require that BSCCO tapes have good mechanical performances, in addition
*
Corresponding author. Tel.: +86-2483682222; fax: +862423915211. E-mail address: [email protected] (Z. Lu).
to current transport capacity, to resist the heat stress and hoop stress. Therefore, it is important to study the effects of strains on the AC critical current of the Bi-based tapes. Several studies have examined the tensile strain effects on the DC critical current of Bi-based superconducting tapes or wires [1–15], but no papers on the strain effects on the AC critical current of Bi-based superconducting tapes or wires. This paper explores the axial tensile strain effects on the AC critical current of Bi-2223 superconducting tapes.
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02243-8
Z. Lu et al. / Physica C 386 (2003) 154–157 Table 1 Details of the specimens No.
Ag19
AgMn61
Matrix Filaments Dimension (mm2 ) Ic (A) DC Ic (A) AC
Ag 19 3:86 0:28 13.0 10.0
Ag–0.5%Mn 37 4:12 0:28 25.7 20
155
terion was selected to determine the AC critical current. The AC voltage includes the superconducting voltage and induction voltage, induction voltage is influenced by the voltage contact points [19]. In this paper, the voltage contact points were soldered at the face center of the tape, and the area enclosed by the signal wires was minimized. DC critical current was measured by a standard fourprobe method, a 5 lV/cm field criterion was also selected to determine the critical current.
2. Experimental The Bi-2223/Ag and Bi-2223/AgMn superconducting tapes were fabricated by the powder-intube method [16]. Details of the specimens are listed in Table 1. The critical current listed in Table 1 were determined by a 5 lV/cm field criterion. Two samples of Ag19 and AgMn61 were tested. For axial strains vs critical current measurements, a new facility of 300–2000 N capacity driven by a servo-motor was fabricated [17]. The specimen is soldered between two stainless-steel rods, one of them being movable. The stress is applied to the specimen by the movable rod connected to a dynamometer. A displacement linear voltage differential transformer (LVDT) is used to monitor the sample elongation. Gauge length of 20–25 mm was used for all tests and was defined as the distance between the ends of the stainless-steel rods. Strain is calculated as e ¼ D=L0 , where L0 is the initial gauge length and D is the displacement measured by LVDT. The specimen was cooled slowly in liquid nitrogen to avoid tensile preloads from thermal contraction. Stepped-loading procedure was used to slowly apply increasing strain at an increment of 0.02–0.05% to allow simultaneous measurement of both AC critical current and DC critical current. When a given strain was obtained, DC critical current was measured before and after measuring an AC critical current curve in the same condition and environment and the same piece of sample, respectively. For AC critical current measurements, a standard four-probe arrangement with voltage taps separation of 10 mm was used to get the voltage and phase h by locking-in technique, used to measure AC loss of superconductor [18], at a given AC current of 50 Hz, a 5 lV/cm field cri-
3. Experimental results and analysis The measured AC and DC V –I curves are shown in Fig. 1. The AC voltage is higher than DC voltage, and the voltage contact points have influence on the AC voltage. In order to determine the AC critical current, the production of measured AC voltage by the cosine of the phase h was used as AC voltage. A 5 lV/cm field criterion was used to determine the AC and DC critical current, as shown in Fig. 1. The AC critical current determined by 1 lV/cm field criteria is too small compared with the DC critical current, and the tape is still at superconducting state transporting AC current. If 10 lV/cm field criterion was adopted, the superconductor–normal conductor transfer has already been finished. The axial tensile strain e vs normalized AC and DC critical current Icn curves Icn ðeÞ at 77 K for
Fig. 1. The AC and DC V –I curves and criteria for determining the AC and DC critical current.
156
Z. Lu et al. / Physica C 386 (2003) 154–157
Fig. 2. The axial tensile strain dependence of AC and DC critical current of 19-filament Bi-2223/Ag superconducting tapes.
Fig. 3. The axial tensile strain dependence of AC and DC critical current of 61-filament Bi-2223/AgMn superconducting tapes.
specimens Ag19 and AgMn61 are shown in Figs. 2 and 3, respectively. The normalized critical current Icn equals Ic =Ic0 , where Ic0 is the zero-strain Ic value. The AC Icn ðeÞ curves of Ag19 and AgMn61 are of the same shape of that of DC Icn ðeÞ curves. The AC critical current Icn remains constant when the strain is small, and decreases slowly as the strain increases. The critical current Icn begins rapid irreversible degradation when the strain is up to a limit, which is written as e0:9 , denoting the strain value when the normalized critical current is 0.9. The e0:9 value of samples Ag19A and AgMn61 are 0.32%, and 0.34%, respectively.
When the strain is greater than e0:9 the normalized AC critical current is greater than normalized DC critical current. In another word, the e0:9 of the AC critical current is greater than that of DC critical current. The normalized AC critical current of Ag19 is 0.67 at e ¼ 0:42%, while the DC Icn is 0.58. The characteristic that AC critical current can endure greater strain and the normalized AC critical current is greater than DC Icn makes it possible to adopt e0:9 of DC critical current instead of that of AC critical current as the criteria for application superconductor design, because it is easy to measure e0:9 of DC critical current. The AC critical current Icn vs tensile strain e curves Icn ðeÞ of Ag19 and AgMn61 can also be described by the formula as [17,20]: e b Icn ¼ 1 ð1Þ a where the a and b are constants, a, the strain value when the critical current becomes zero, equals 0.0048 (0.48%), and 0.0044 (0.44%) for specimens Ag19 and AgMn61, respectively, b equals 6.37 and 6.75 for specimens Ag19, and AgMn61, respectively. Eq. (1) fits well the Icn ðeÞ curves of Ag19 and AgMn61, as shown by the open symbols in Fig. 4. Why AC critical current can endure larger strain? One explanation is related to the different transport mechanism of AC and DC superconducting current. Another explanation is as follows: the DC voltage VDC ¼ Vsc þ Vsh , the AC voltage VAC ¼ Vsc þ Vsh þ Vi , where Vsc , Vsh and Vi is the
Fig. 4. The measured and fitted AC Icn ðeÞ curves of Ag19 and AgMn61 superconducting tapes.
Z. Lu et al. / Physica C 386 (2003) 154–157
voltage of the superconductor, the sheath materials and induced voltage, VAC > VDC as shown in Fig. 1. The induction voltage depends on the whole current transporting the tapes. When strain is large enough to deteriorate the transport capacity of superconducting tapes, more current flows in the sheath, the DC voltage VDC increase, and the AC voltage VAC increase either, but less in relative amplitude, this has been proved by the AC and DC V –I curves when the strain is greater than the irreversible strain limits e0:9 [17], the DC critical current decreases greater in relative amplitude than AC critical current, so the normalized AC critical current is greater than DC Icn determined by the same field criteria at the same strain.
4. Conclusions 5 lV/cm field criteria can be used to determine the AC and DC critical current. The AC and DC Icn ðeÞ of Ag and AgMn/Ag sheathed Bi-2223 superconducting composite tapes are almost the same when the axial tensile strain is less than e0:9 , when the axial tensile strain is larger than e0:9 , the AC critical current decrease less rapidly than DC critical current, and at the same strain, the normalized AC critical current is greater than normalized DC critical current. This may be resulted from the greater relative increasement in DC voltage than that in AC voltage when the strain is large enough to deteriorate the transport capacity of the tape. The AC Icn ðeÞ curves have the empirb ical formula as Icn ¼ 1 ðe=aÞ , where a and b are constants.
157
Acknowledgements This paper was supported by National Natural Science Foundation of China (granted no. 19474010), and by the National Center for R&D on Superconductivity of China (granted no. 863CD010104), and by the Chinese Foundation of Doctoral Education (granted no. 96014516). References [1] J. Schwartz, H. Sekine, et al., IEEE Trans. Magn. 27 (1991) 1247. [2] H. Sekine, J. Schwartz, et al., J. Appl. Phys. 70 (1991) 1596. [3] J.W. Ekin et al., Appl. Phys. Lett. 61 (1992) 858. [4] L. Gherardi et al., Cryogenics 34 (1994) 781. [5] R. Wesche et al., Cryogenics 36 (1996) 419. [6] B. ten Haken et al., IEEE Trans. Appl. Supercond. 5 (1995) 1298. [7] B. ten Haken et al., IEEE Trans. Magn. 32 (1996) 2720. [8] B. ten Haken et al., IEEE Trans. Appl. Supercond. 7 (1997) 2034. [9] Y.K. Huang, B. ten Haken, et al., IEEE Trans. Appl. Supercond. 9 (1999) 2702. [10] W. Goldacker et al., IEEE Trans. Appl. Supercond. 5 (1995) 1835. [11] K. Katagiri et al., Cryogenics 36 (1996) 491. [12] K. Katagiri et al., Cryogenics 38 (1998) 283. [13] K. Katagiri et al., Cryogenics 39 (1999) 453. [14] B. Ullmann et al., IEEE Trans. Appl. Supercond. (1997) 2042. [15] Z. Lu et al., Physica C 337 (2000) 150. [16] C.S. Li et al., Physica C 282–287 (1997) 2611. [17] Z. Lu, Stress and strain effects on the critical current of Bibased superconducting tapes, Ph.D. thesis, Northeastern University, Shenyang, PRC, 2001. [18] J. Li et al., Physica C, these Proceedings. [19] M. Ciszek et al., Physica C 233 (1994) 203. [20] Z. Lu et al., Physica C, these Proceedings.