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A study on I–V characteristics of conduction-cooled HTS coil
Physica C 463–465 (2007) 1276–1280 www.elsevier.com/locate/physc
A study on I–V characteristics of conduction-cooled HTS coil M.-H. Sohn *, S. Kim, K.-D. Sim, C.-H. Min, E.-Y. Lee, K.-C. Seong, Y.-K. Kwon, H.-J. Kim Superconducting Devices and Cryogenics Group, Korea Electrotechnology Research Institute, 28-1 Seongju-dong, Changwon, Gyeongnam 641-120, South Korea Accepted 16 March 2007 Available online 2 June 2007
Abstract A conduction-cooled high-temperature superconducting (HTS) coil consisting of two double pancake coils was fabricated. The current–voltage (I–V) characteristics of HTS coil were obtained at different temperatures by using GM cryocooler. Using OPERA 2D, magnetic field (Br) perpendicular to the surface of the tape at each layer of HTS coil was obtained. In order to compare with the measured values, I–V curve of the HTS coil was simulated, in the basis of the magnetic field dependence of the critical current (Ic) in Bi-2223 tapes and index of n-value. Results showed pretty good agreement between the simulated and the measured critical currents at 77.3 K and 40 K, with a bit difference under simple assumption of index of n value. Ó 2007 Elsevier B.V. All rights reserved. PACS: 84.71.Ba; 84.71.Mn Keywords: I–V curve characteristics; HTS coil; Bi-2223 tape; Critical currents
1. Introduction Recently, it has become possible to fabricate long scale Ag or Ag alloy sheathed Bi based HTS tapes [1,2]. Hence there is an interest in developing superconducting devices for high efficiency and high power. Many works have been carried out for developing HTS applications; even some of them constructed superconducting devices to realize the practical applications [3–5]. It is widely considered that HTS coil is one of the key components for fabricating superconducting devices. The increment of the use of high-temperature superconductors for advanced power applications has generated a lot of interest in the acquisition of the I–V curve characteristics. Here, we have to consider that I–V curve characteristics strongly depend on various magnetic field strength generated in HTS magnets in the applications such as transformers, motors, genera-
*
Corresponding author. Tel.: +82 55 280 1692; fax: +82 55 280 1696. E-mail address: [email protected] (M.-H. Sohn).
0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.03.490
tors, SMES and cryogen-free magnets. In this respect, the design of SC electromagnets requires the knowledge of Ic and I–V curve characteristics in the coils. For HTS tapes, although critical currents of the magnetic field dependence are known, the actual Ic of a specific winding geometry is difficult to predict because of the large field variations across the cross-section of the tape resulting in non-homogeneous current flow. Recently, a mathematical model of the I–V characteristics of Bi-2223 magnets was suggested [6,7]. This model is suitable for coil designs where the field variation across the tape is low. Herein, we fabricated small HTS coil by using two double pancake sub-coils. I–V curve characteristics of HTS coil were measured at different temperatures using GM cryocooler. Not only to have a good comparison but also to evaluate the damage of the HTS conductor during the winding process, simulation on I–V curve of the HTS coil is carried out, on the basis of the magnetic field dependence of Ic in Bi-2223 tapes and index of n-value. This paper focuses primarily on fabrication of HTS coil and comparisons of measured and simple calculated results of HTS coil.
M.-H. Sohn et al. / Physica C 463–465 (2007) 1276–1280
1277
2. Experimental Two double pancake sub-coils were manufactured by the react and wind fabrication method. The coils were fabricated with HTS tapes using wet winding method under the condition of 800 gf tension and 1 rpm speed. Here, the epoxy painting on the tape was carried out with brush. The wound coil was fixed with a clamping system, and then it was cured at room temperature for one day. The material of bobbins for sub-coils was brass. Fig. 1 shows each bobbin for a double pancake coil consist of two bobbin-rings having an inner support plate and two side plates. Fig. 2 is a schematic diagram of HTS coil consisting of two double pancake coils, sub-coil A and B. In each sub-coil, approximately 45 turns were wound in the upper and bottom pancakes, respectively. Table 1 shows specification of HTS conductor, brass tapes-reinforced Bi-2223 4-ply tapes. These tapes were produced by AMSC (American Superconductor Corporation). It was lapped with Kapton tape for insulation. Ic of Bi-2223 4ply tape was 274 A at 77 K and self-field. The specification of the HTS coil is listed in Table 2. Two sub-coils were connected in series to form a HTS coil. Assembled HTS coil was shown in Fig. 2b. HTS coil was cooled down to approximately 20 K by using two 2-stages GM cryocoolers. I–V measurement system attached with quench protection circuit consist of a protection switch and a protection resistor connected each other in parallel, was employed to measure the I–V curve. The HTS magnet was serially connected to the measurement unit. During charging to HTS magnet, protection switch is ON. At moment of quench detection, switch is off and then currents flow protection resistor. So, energy charged in the magnet will be vanished. Data acquisition was conducted by PC, SCXI-DAQ system an 8 V, 500 A power supply and labview program.
Fig. 2. (a) Dimensions of small HTS coil, (b) assembled HTS coil.
Table 1 Specifications of Bi-2223 4-ply HTS tape Average thickness, laminated (mm) Average thickness, Kapton insulated (mm) Max width, Kapton insulated (mm) End sample 10 m Ic at 77 K, self-field, 1 lV/cm (A) Number of HTS tapes
0.58 0.73 4.50 274 2
Table 2 Specifications of a HTS coil Number of turns Inner diameter (mm) Outer diameter (mm) Height (mm) Critical current at 77.3 K (A) Number of double pancake coils
n Is Ic
179 170 245 24 97 2
3. Results and discussion
Vs ¼Vc
It is important to investigate I–V characteristics, not only in the aspect of basic physics but also in the viewpoint of practical applications. The approximate power law characteristics:
Eq. (1) allows us to the model of the flux motion behavior. Here, Is is the current flow in the superconducting cores. The exponent n-value is affected by various intrinsic and
Fig. 1. (a) Assembled bobbin for double pancake coils, (b) its part before assembling.
ð1Þ
M.-H. Sohn et al. / Physica C 463–465 (2007) 1276–1280
extrinsic factors [8]. In the HTS pancake coil, voltage Vi of ith layer of HTS coil with respect to operating current I can be obtained as follows: n n I I ¼ li E c ð2Þ V i ¼ V ic I ic I ic where li is the length of ith layer of HTS coil at I = Ic and usually Ec electric field criterion 1 lV/cm. So, V of HTS coil can be obtained by summing Vi as follows: n X n m m m X X I I Vi ¼ V ic ¼ ðli Ec Þ ð3Þ V ¼ I I ic ic i¼1 i¼1 i¼1 To calculate I–V curves of HTS coil, in this study, we simply assume that n-value is constant, for example 17 at 77.3 K. Also, Ic of AMSC Bi-2223 HTS tape as a function of temperature under externally applied perpendicular magnetic field can be obtained from Young’s results [9]. Magnetic field intensity is in proportion to the operating current of HTS coil in case that the bobbin and its components were non-magnetic. Fig. 3 shows magnetic field distribution of HTS coil under the condition of operating current 1 A, analyzed by commercial software Opera of Vector Fields. Fig. 3a and b show the distribution of the radial (Br) and axial self-field (Bz) components of HTS coil, normalized to the current. Such results have been obtained under the assumption of homogeneous current distribution in all the windings. As shown in Fig. 3a, maximal value of Br were observed near the middle of the upper part of subcoil A and near the middle of the lower part of sub-coil B. In this HTS coil, Br varied from approximately 20.04 G/A to 20.04 G/A in one side to the opposite side, which passes through zero at the center plane between sub-coil A and B. Bz is maximal, +28.03 G/A, at the inner windings of HTS coil. Because of the high anisotropy in the field dependent characteristics of the Bi-2223 tape, in the configuration of this HTS coil, Br, perpendicular component on the Bi-2223 tape is the dominant field component determining Ic of the HTS coil. Therefore, we neglect the role of Bz, parallel component on the Bi-2223 tape for the determination of Ic. Distribution of Br at midpoint of Bi-2223 tape in each sub-coil was shown in Fig. 4. From upper sub-coil to bottom sub-coil, maximum of Br were 14.85 G/A,
25
(Upper) sub-coil A (Bottom) sub-coil A (Upper) sub-coil B (Bottom) sub-coil B
20 15 10
Br [G/A]
1278
5 0 -5 -10 -15 -20 80
85
90
95
100
105
110
115
120
125
r [mm] Fig. 4. The radial component of the self-field Br at midpoint of Bi-2223 tape in each sub-coils of HTS coil.
4.44 G/A, 4.85 G/A, 15.04 G/A, respectively. For the calculation of I–V curve of HTS coil, we used Br at midpoint of Bi-2223 tape in each layer of HTS coil. Fig. 5 shows the measured and the calculated I–V curves of HTS coil at 77.3 K. A critical current Ic was derived from the measured I–V curve. Calculated Ic of HTS coil was 93.5 A, about 96.4% of 97 A, Ic measured actually at 77.3 K. Hereafter, Ic was calculated using the 1 lV/cm criterion. Fig. 6 shows I–V curves of HTS coil measured at various temperatures. Unfortunately, maximum current of power supply used in this study was 500 A. In this reason, Ic could not be measured below 35.6 K, highest temperature point in HTS coil. The position of temperature sensor was shown in Fig. 2. At various temperatures of HTS coil, i.e. in the order of 39.4 K, 45.7 K, 50.0 K and 54.8 K, Ic of HTS coil were obtained in the order of 459 A, 362 A, 306 A, 252 A. In the case of 39.4 K, Ic was approximately 4.7 times as large as Ic in comparison with other temperature, 77.3 K. From these experiments, it is considered that no serious damage in HTS coil used in this study occurred during the winding and operating. We simulated I–V curve of HTS coil at 40 K and the result was shown in Fig. 7. Calculated Ic of HTS coil was 432 A, about 94% of 460 A, Ic measured actually at 39.4 K. Fig. 8 shows the load lines of HTS coil. Solid line
Fig. 3. (a) The radial component of the self-field, Br, of HTS coil for a current of 1 A, (b) the axial self-field component, Bz.
M.-H. Sohn et al. / Physica C 463–465 (2007) 1276–1280 100
1279
1000 I-Br characteristics obtained from reference [9]
90
HTS coil [113 m] measured calculated
80
Average uniform field Maximum uniform field
800
60
Current/I [A]
Voltage [mV]
70
77.3 K
50 40 Ic = 93.5 A
30
485 A
600
432 A
40 K
400 106 A 93.5 A
Ic = 97.0 A 200
20 1 μV/cm
10
85 A
0
0 0
20
40
60
80
100
120
140
77.3 K 0
2000
HTS Coil [113 m] T = 54.8K T = 50.0K T = 45.7K T = 39.4K T = 35.6K T = 30.0K T = 25.0K
25 20
8000
10000
12000
that equals the maximal field value. Measured values were located between such two load lines. Under simple assumption of constant index of n-value, we obtained minor difference in between measured and calculated values of Ic. We considered that such minor difference was originated from simple assumption of index of n-value. Here, expectation of current variation as a function of radial magnetic field, Br is not significantly apart from measured values. In order to obtain precise expectation for Ic, we need to modify assumption of index of nvalue in the further study.
40
30
6000
Fig. 8. I–B characteristics of HTS coil.
Fig. 5. I–V curves of HTS coil at 77.3 K.
35
4000
Radial Magnetic Field Intensity/Br [G]
Current [A]
Voltage [mV]
460 A
15 1μV/cm 10 5
4. Conclusions
0 0
50
100
150
200
250
300
350
400
450
500
Current [A] Fig. 6. I–V curves of HTS coil at different temperatures.
100 90 80
HTS coil [113 m] measured calculated
Voltage [mV]
70 60
40 K Ic = 432 A
50 40
39.4 K Ic = 460 A
30 20
Acknowledgement
1 μ V/cm
10 0
0
100
HTS coil was fabricated and tested electrical characteristics. I–V curves of HTS coil cooled by conduction have been measured at different temperatures and in the range of current, 0–500 A. Ic of HTS coil was measured as 460 A at 39.4 K. Calculated Ic of HTS coil was 432 A at 40 K. HTS coil was successfully fabricated without damage. Also, I–V curve of HTS coil was experimentally obtained, and under simple assumption of constant index of n-value, we calculated I–V curve. In comparison with the measured I–V curves, we confirmed that minor difference was found in the calculated I–V curves. For precise expectation for Ic, we will do further study near future, considering modified assumption of index of n-value, which depends on temperature and magnetic field.
200
300
400
500
600
Current [A] Fig. 7. I–V curves of HTS coil at 40 K.
means the load line under the assumption of the uniform field. Such value is equal to the average field value through the tape cross-section. Dot line means when a uniform field
This work was supported by a Grant from Korea Electrotechnology Research Institute of Basic Science Research Program funded by the Ministry of Science and Technology, Republic of Korea. References [1] http://www.amsuper.com/products/htsWire/index.cfm. [2] http://www.sei.co.jp/super/hts_e/index.html.
1280
M.-H. Sohn et al. / Physica C 463–465 (2007) 1276–1280
[3] Y.K. Kwon, M.H. Sohn, S.K. Baik, E.Y. Lee, J.M. Kim, T.S. Moon, H.J. Park, Y.C. Kim, K.S. Ryu, IEEE Trans. Appl. Supercond. 15 (2005) 2194. [4] G. Snitchler, B. Gamble, S.S. Kalsi, IEEE Trans. Appl. Supercond. 15 (2005) 2206. [5] W. Nick, G. Nerowski, H.-W. Neumueller, M. Frank, P. van Hasselt, J. Frauenhofer, F. Steinmeyer, Physica C 372–376 (2002) 1506. [6] M. Haverkamp, B. ten Haken, L. Bottura, H.H.J. ten Kate, Physica C 372–376 (2002) 1356.
[7] Y. Wolfus, Y. Fleger, A. Friedman, F. Kopansky, B. Kalisky, Y. Yeshurun, Z. Bar-Haim, Z. Ron, L. Ying, N. Pundak, Physica C 401 (2004) 222. [8] W.H. Warnes, L.D. Cooley, D.C. Larbalestier, Adv. Cryog. Eng. Mater. 34 (1988) 1009. [9] M.A. Young, J.A. Demko, R.C. Duckworth, J.W. Lue, M.J. Gouge, M.O. Pace, IEEE Trans. Appl. Supercond. 13 (2003) 2964.
A study on I–V characteristics of conduction-cooled HTS coil M.-H. Sohn *, S. Kim, K.-D. Sim, C.-H. Min, E.-Y. Lee, K.-C. Seong, Y.-K. Kwon, H.-J. Kim Superconducting Devices and Cryogenics Group, Korea Electrotechnology Research Institute, 28-1 Seongju-dong, Changwon, Gyeongnam 641-120, South Korea Accepted 16 March 2007 Available online 2 June 2007
Abstract A conduction-cooled high-temperature superconducting (HTS) coil consisting of two double pancake coils was fabricated. The current–voltage (I–V) characteristics of HTS coil were obtained at different temperatures by using GM cryocooler. Using OPERA 2D, magnetic field (Br) perpendicular to the surface of the tape at each layer of HTS coil was obtained. In order to compare with the measured values, I–V curve of the HTS coil was simulated, in the basis of the magnetic field dependence of the critical current (Ic) in Bi-2223 tapes and index of n-value. Results showed pretty good agreement between the simulated and the measured critical currents at 77.3 K and 40 K, with a bit difference under simple assumption of index of n value. Ó 2007 Elsevier B.V. All rights reserved. PACS: 84.71.Ba; 84.71.Mn Keywords: I–V curve characteristics; HTS coil; Bi-2223 tape; Critical currents
1. Introduction Recently, it has become possible to fabricate long scale Ag or Ag alloy sheathed Bi based HTS tapes [1,2]. Hence there is an interest in developing superconducting devices for high efficiency and high power. Many works have been carried out for developing HTS applications; even some of them constructed superconducting devices to realize the practical applications [3–5]. It is widely considered that HTS coil is one of the key components for fabricating superconducting devices. The increment of the use of high-temperature superconductors for advanced power applications has generated a lot of interest in the acquisition of the I–V curve characteristics. Here, we have to consider that I–V curve characteristics strongly depend on various magnetic field strength generated in HTS magnets in the applications such as transformers, motors, genera-
*
Corresponding author. Tel.: +82 55 280 1692; fax: +82 55 280 1696. E-mail address: [email protected] (M.-H. Sohn).
0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.03.490
tors, SMES and cryogen-free magnets. In this respect, the design of SC electromagnets requires the knowledge of Ic and I–V curve characteristics in the coils. For HTS tapes, although critical currents of the magnetic field dependence are known, the actual Ic of a specific winding geometry is difficult to predict because of the large field variations across the cross-section of the tape resulting in non-homogeneous current flow. Recently, a mathematical model of the I–V characteristics of Bi-2223 magnets was suggested [6,7]. This model is suitable for coil designs where the field variation across the tape is low. Herein, we fabricated small HTS coil by using two double pancake sub-coils. I–V curve characteristics of HTS coil were measured at different temperatures using GM cryocooler. Not only to have a good comparison but also to evaluate the damage of the HTS conductor during the winding process, simulation on I–V curve of the HTS coil is carried out, on the basis of the magnetic field dependence of Ic in Bi-2223 tapes and index of n-value. This paper focuses primarily on fabrication of HTS coil and comparisons of measured and simple calculated results of HTS coil.
M.-H. Sohn et al. / Physica C 463–465 (2007) 1276–1280
1277
2. Experimental Two double pancake sub-coils were manufactured by the react and wind fabrication method. The coils were fabricated with HTS tapes using wet winding method under the condition of 800 gf tension and 1 rpm speed. Here, the epoxy painting on the tape was carried out with brush. The wound coil was fixed with a clamping system, and then it was cured at room temperature for one day. The material of bobbins for sub-coils was brass. Fig. 1 shows each bobbin for a double pancake coil consist of two bobbin-rings having an inner support plate and two side plates. Fig. 2 is a schematic diagram of HTS coil consisting of two double pancake coils, sub-coil A and B. In each sub-coil, approximately 45 turns were wound in the upper and bottom pancakes, respectively. Table 1 shows specification of HTS conductor, brass tapes-reinforced Bi-2223 4-ply tapes. These tapes were produced by AMSC (American Superconductor Corporation). It was lapped with Kapton tape for insulation. Ic of Bi-2223 4ply tape was 274 A at 77 K and self-field. The specification of the HTS coil is listed in Table 2. Two sub-coils were connected in series to form a HTS coil. Assembled HTS coil was shown in Fig. 2b. HTS coil was cooled down to approximately 20 K by using two 2-stages GM cryocoolers. I–V measurement system attached with quench protection circuit consist of a protection switch and a protection resistor connected each other in parallel, was employed to measure the I–V curve. The HTS magnet was serially connected to the measurement unit. During charging to HTS magnet, protection switch is ON. At moment of quench detection, switch is off and then currents flow protection resistor. So, energy charged in the magnet will be vanished. Data acquisition was conducted by PC, SCXI-DAQ system an 8 V, 500 A power supply and labview program.
Fig. 2. (a) Dimensions of small HTS coil, (b) assembled HTS coil.
Table 1 Specifications of Bi-2223 4-ply HTS tape Average thickness, laminated (mm) Average thickness, Kapton insulated (mm) Max width, Kapton insulated (mm) End sample 10 m Ic at 77 K, self-field, 1 lV/cm (A) Number of HTS tapes
0.58 0.73 4.50 274 2
Table 2 Specifications of a HTS coil Number of turns Inner diameter (mm) Outer diameter (mm) Height (mm) Critical current at 77.3 K (A) Number of double pancake coils
n Is Ic
179 170 245 24 97 2
3. Results and discussion
Vs ¼Vc
It is important to investigate I–V characteristics, not only in the aspect of basic physics but also in the viewpoint of practical applications. The approximate power law characteristics:
Eq. (1) allows us to the model of the flux motion behavior. Here, Is is the current flow in the superconducting cores. The exponent n-value is affected by various intrinsic and
Fig. 1. (a) Assembled bobbin for double pancake coils, (b) its part before assembling.
ð1Þ
M.-H. Sohn et al. / Physica C 463–465 (2007) 1276–1280
extrinsic factors [8]. In the HTS pancake coil, voltage Vi of ith layer of HTS coil with respect to operating current I can be obtained as follows: n n I I ¼ li E c ð2Þ V i ¼ V ic I ic I ic where li is the length of ith layer of HTS coil at I = Ic and usually Ec electric field criterion 1 lV/cm. So, V of HTS coil can be obtained by summing Vi as follows: n X n m m m X X I I Vi ¼ V ic ¼ ðli Ec Þ ð3Þ V ¼ I I ic ic i¼1 i¼1 i¼1 To calculate I–V curves of HTS coil, in this study, we simply assume that n-value is constant, for example 17 at 77.3 K. Also, Ic of AMSC Bi-2223 HTS tape as a function of temperature under externally applied perpendicular magnetic field can be obtained from Young’s results [9]. Magnetic field intensity is in proportion to the operating current of HTS coil in case that the bobbin and its components were non-magnetic. Fig. 3 shows magnetic field distribution of HTS coil under the condition of operating current 1 A, analyzed by commercial software Opera of Vector Fields. Fig. 3a and b show the distribution of the radial (Br) and axial self-field (Bz) components of HTS coil, normalized to the current. Such results have been obtained under the assumption of homogeneous current distribution in all the windings. As shown in Fig. 3a, maximal value of Br were observed near the middle of the upper part of subcoil A and near the middle of the lower part of sub-coil B. In this HTS coil, Br varied from approximately 20.04 G/A to 20.04 G/A in one side to the opposite side, which passes through zero at the center plane between sub-coil A and B. Bz is maximal, +28.03 G/A, at the inner windings of HTS coil. Because of the high anisotropy in the field dependent characteristics of the Bi-2223 tape, in the configuration of this HTS coil, Br, perpendicular component on the Bi-2223 tape is the dominant field component determining Ic of the HTS coil. Therefore, we neglect the role of Bz, parallel component on the Bi-2223 tape for the determination of Ic. Distribution of Br at midpoint of Bi-2223 tape in each sub-coil was shown in Fig. 4. From upper sub-coil to bottom sub-coil, maximum of Br were 14.85 G/A,
25
(Upper) sub-coil A (Bottom) sub-coil A (Upper) sub-coil B (Bottom) sub-coil B
20 15 10
Br [G/A]
1278
5 0 -5 -10 -15 -20 80
85
90
95
100
105
110
115
120
125
r [mm] Fig. 4. The radial component of the self-field Br at midpoint of Bi-2223 tape in each sub-coils of HTS coil.
4.44 G/A, 4.85 G/A, 15.04 G/A, respectively. For the calculation of I–V curve of HTS coil, we used Br at midpoint of Bi-2223 tape in each layer of HTS coil. Fig. 5 shows the measured and the calculated I–V curves of HTS coil at 77.3 K. A critical current Ic was derived from the measured I–V curve. Calculated Ic of HTS coil was 93.5 A, about 96.4% of 97 A, Ic measured actually at 77.3 K. Hereafter, Ic was calculated using the 1 lV/cm criterion. Fig. 6 shows I–V curves of HTS coil measured at various temperatures. Unfortunately, maximum current of power supply used in this study was 500 A. In this reason, Ic could not be measured below 35.6 K, highest temperature point in HTS coil. The position of temperature sensor was shown in Fig. 2. At various temperatures of HTS coil, i.e. in the order of 39.4 K, 45.7 K, 50.0 K and 54.8 K, Ic of HTS coil were obtained in the order of 459 A, 362 A, 306 A, 252 A. In the case of 39.4 K, Ic was approximately 4.7 times as large as Ic in comparison with other temperature, 77.3 K. From these experiments, it is considered that no serious damage in HTS coil used in this study occurred during the winding and operating. We simulated I–V curve of HTS coil at 40 K and the result was shown in Fig. 7. Calculated Ic of HTS coil was 432 A, about 94% of 460 A, Ic measured actually at 39.4 K. Fig. 8 shows the load lines of HTS coil. Solid line
Fig. 3. (a) The radial component of the self-field, Br, of HTS coil for a current of 1 A, (b) the axial self-field component, Bz.
M.-H. Sohn et al. / Physica C 463–465 (2007) 1276–1280 100
1279
1000 I-Br characteristics obtained from reference [9]
90
HTS coil [113 m] measured calculated
80
Average uniform field Maximum uniform field
800
60
Current/I [A]
Voltage [mV]
70
77.3 K
50 40 Ic = 93.5 A
30
485 A
600
432 A
40 K
400 106 A 93.5 A
Ic = 97.0 A 200
20 1 μV/cm
10
85 A
0
0 0
20
40
60
80
100
120
140
77.3 K 0
2000
HTS Coil [113 m] T = 54.8K T = 50.0K T = 45.7K T = 39.4K T = 35.6K T = 30.0K T = 25.0K
25 20
8000
10000
12000
that equals the maximal field value. Measured values were located between such two load lines. Under simple assumption of constant index of n-value, we obtained minor difference in between measured and calculated values of Ic. We considered that such minor difference was originated from simple assumption of index of n-value. Here, expectation of current variation as a function of radial magnetic field, Br is not significantly apart from measured values. In order to obtain precise expectation for Ic, we need to modify assumption of index of nvalue in the further study.
40
30
6000
Fig. 8. I–B characteristics of HTS coil.
Fig. 5. I–V curves of HTS coil at 77.3 K.
35
4000
Radial Magnetic Field Intensity/Br [G]
Current [A]
Voltage [mV]
460 A
15 1μV/cm 10 5
4. Conclusions
0 0
50
100
150
200
250
300
350
400
450
500
Current [A] Fig. 6. I–V curves of HTS coil at different temperatures.
100 90 80
HTS coil [113 m] measured calculated
Voltage [mV]
70 60
40 K Ic = 432 A
50 40
39.4 K Ic = 460 A
30 20
Acknowledgement
1 μ V/cm
10 0
0
100
HTS coil was fabricated and tested electrical characteristics. I–V curves of HTS coil cooled by conduction have been measured at different temperatures and in the range of current, 0–500 A. Ic of HTS coil was measured as 460 A at 39.4 K. Calculated Ic of HTS coil was 432 A at 40 K. HTS coil was successfully fabricated without damage. Also, I–V curve of HTS coil was experimentally obtained, and under simple assumption of constant index of n-value, we calculated I–V curve. In comparison with the measured I–V curves, we confirmed that minor difference was found in the calculated I–V curves. For precise expectation for Ic, we will do further study near future, considering modified assumption of index of n-value, which depends on temperature and magnetic field.
200
300
400
500
600
Current [A] Fig. 7. I–V curves of HTS coil at 40 K.
means the load line under the assumption of the uniform field. Such value is equal to the average field value through the tape cross-section. Dot line means when a uniform field
This work was supported by a Grant from Korea Electrotechnology Research Institute of Basic Science Research Program funded by the Ministry of Science and Technology, Republic of Korea. References [1] http://www.amsuper.com/products/htsWire/index.cfm. [2] http://www.sei.co.jp/super/hts_e/index.html.
1280
M.-H. Sohn et al. / Physica C 463–465 (2007) 1276–1280
[3] Y.K. Kwon, M.H. Sohn, S.K. Baik, E.Y. Lee, J.M. Kim, T.S. Moon, H.J. Park, Y.C. Kim, K.S. Ryu, IEEE Trans. Appl. Supercond. 15 (2005) 2194. [4] G. Snitchler, B. Gamble, S.S. Kalsi, IEEE Trans. Appl. Supercond. 15 (2005) 2206. [5] W. Nick, G. Nerowski, H.-W. Neumueller, M. Frank, P. van Hasselt, J. Frauenhofer, F. Steinmeyer, Physica C 372–376 (2002) 1506. [6] M. Haverkamp, B. ten Haken, L. Bottura, H.H.J. ten Kate, Physica C 372–376 (2002) 1356.
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