- Email: [email protected]
MRI HTS Magnets
Available online at www.sciencedirect.com
ScienceDirect Physics Procedia 65 (2015) 149 – 152
27th International Symposium on Superconductivity, ISS 2014
Current bypassing properties by thermal switch for PCS application on NMR/MRI HTS magnets S.B. Kima,*, M. Takahashia, R. Saitoa, Y.J. Parkb, M.W. Leeb, Y.K. Ohb, H.S. Annb a
Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka , Kita-ku , Okayama 700-8530, JAPAN b K·Joins, Inc. 913C H-1 KIST Venture Town Hwarangro 14 gil 5, Seongbuk-gu, Seoul 136-791, KOREA
Abstract We develop the compact NMR/MRI device using high temperature superconducting (HTS) wires with the persistent current mode operating. So, the joint techniques between 2G wires are very important issue and many studies have been carried out. Recently, the K·JOINS, Inc. has developed successfully the high performance superconducting joints between 2G wires by partial melting diffusion and oxygenation annealing process [1]. In this study, the current bypassing properties in a loop-shaped 2G wire are measured experimentally to develop the permanent current switch (PSC). The current bypassing properties of loop-shaped test coil wound with 2G wire (GdBCO) are evaluated by measured the self-magnetic field due to bypassed current by Hall sensors. The strain gauge was used as heater for persistent current switch, and thermal properties against various thermal inputs were investigated experimentally. © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-reviewunder underresponsibility responsibility of the Program Committee. Peer-review of the ISSISS 20142014 Program Committee Keywords:NMR relaxometry; HTS coil magnet; joints between 2G wires; persistent current switch (PCS); permanent current mode
1. Introduction The low temperature superconducting (LTS) coils are used in present NMR / MRI devices and liquid helium is used for their cooling. However, it is possible to reduce the operating costs by manufacturing the superconducting magnet which is consisted of the high temperature superconducting (HTS) coil using liquid nitrogen cooling. We develop the compact NMR/MRI device using HTS wires with the persistent current mode operating. So, the joint techniques between HTS wires are very important issue and many studies have been carried out. Recently, the K·JOINS, Inc. has developed successfully the high performance superconducting joints between 2G wires by partial melting diffusion and oxygenation annealing process [1]. In general, the thermal heaters are usually used for persistent current switch (PCS), and the superconducting region turn into the normal state by a heater. In this study, the current bypassing properties in a loopshaped 2G wire are measured experimentally to develop the PCS The current bypassing properties of loop-shaped test coil wound with 2G wire (GdBCO) are evaluated by measured the self-magnetic field due to bypassed current by Hall sensors. The strain gauge was used as heater for persistent current switch, and thermal properties against various thermal inputs were investigated experimentally.
*Corresponding author. Tel.: +81-86-251-8116; fax: +81-86-251-8110. E-mail address: [email protected]
1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the ISS 2014 Program Committee doi:10.1016/j.phpro.2015.05.088
150
S.B. Kim et al. / Physics Procedia 65 (2015) 149 – 152
2. Experimental details Fig.1 shows the (a) schematic drawing of the proposed compact NMR magnet using the high performance superconducting joints and (b) photograph of the loop-shaped test coil with high performance superconducting joints between 2G (GdBCO) wires by partial melting diffusion and oxygenation annealing process. The proposed NMR superconducting magnet wound with 2G wires to be operating in the persistent current mode. The one layer test coil wound with GdBCO wire without stabilizer is prepared to study the PCS as shown in Fig. (b). A superconducting joint in Fig.1 (b) is prepared by K·JOINS, Inc.. It is necessary to install a PCS in NMR/MRI HTS magnets operating in persistent current mode. The current bypassing properties are determined by PCS. Fig.2 shows the schematic view of the test coils wound with GdBCO wire (a) with normal joint by soldering and (b) GdBCO loop-shaped test coil with superconducting joint. In test coil with normal joint by soldering, the thermal couples and voltage taps are attached to measure the current bypassing properties. The interval among T1, T2 and T3 is 2 cm (Fig.2 (a)). The intervals between V1 and V2, V2 and V3, and V3 and V4 are 32 cm, 1.5 cm and 2 cm respectively (Fig.2 (a)). In both test coils, the two heaters (strain gauge) and the Hall sensors are attached to measure the current bypassing properties. Table 1 shows specifications of GdBCO 2G wire and heater. Table 2 shows applied thermal heat by the heater. In test coils with normal joint and superconducting joint, the currents of 100 A and 10 A are transported respectively because the critical current at superconducting joint is 17 A. The current bypassing properties of loop-shaped test coils wound with 2G wire (GdBCO) are evaluated by measured the self-magnetic field due to bypassed current by Hall sensors. Filler Caps
Double pancake coil
Level Sensor
PCS
+
Heater
I
(b)
Superconducting joint
(a)
䠉 DC power supply
Probe Assembly
Liquid Nitrogen Bath
Superconducting joint part
Super-conducting Coil
Fig. 1. (a) Schematic drawing of the proposed compact NMR magnet using the high performance superconducting joints; (b) photograph of the loop-shaped test coil with high performance superconducting joints between 2G (GdBCO) wires by partial melting diffusion and oxygenation annealing process. 1st GdBCO wire
T1
T3
V2
V3
V4
V1
(a) 䞉䞉䞉Voltage tap
1&2
Normal joint Current part lead
3&4
T2
V2 6.2 cm V3
Superconducting joint part
V1 24.8 cm
Current lead V4
(b) 䞉䞉䞉Voltage tap 䞉䞉䞉Hall sensor 䞉䞉䞉 Heater Fig. 2. The schematic view of the test coils wound with GdBCO wire (a) with normal joint by soldering and (b) GdBCO loop-shaped test coil with superconducting joint. 䞉䞉䞉Thermocouple
䞉䞉䞉 Heater
䞉䞉䞉Hall sensor
Table 1. Specifications of GdBCO 2G wire and heater Components Parameters GdBCO conductor (Ag/GdBCO/Buffer/Substrate/Ag)
Heater (Strain gauge)
Specification
Critical current at 77K Length Width Thickness Thickness of upper Ag layer Thickness of GdBCO layer Thickness of buffer layer Thickness of substrate Thickness of bottom Ag layer
114 A 100, 105 mm 4 mm 55 μm 2 μm 1 μm 㹼0.2 μm 50 μm
Thickness Length Width Resistance
50 μm 11 mm 5 mm 1000 :
1.8 μm
151
S.B. Kim et al. / Physics Procedia 65 (2015) 149 – 152 Table 2. Applied thermal heat by the heater The number of times of supply
The number of heaters
Times [s]
Loading interval [s]
Joule heating [J]
Once
1
0.5 1* 2 0.5 1* 2
-
1-5 1-5 1-6 1-5 1-6 1-5 5 5 5 5 5 5
2
Twice
1
0.5 2,4 1 2,4 2 2,4 2 0.5 2,4 1 2,4 2 2,4,6 * Applied various input heating for superconducting joint wire
3. Results and discussion (normal joint wire) 3.1. Single pulse heating Fig.3 shows the generated voltage traces, and the 1/10 scaled heat input and measured self-magnetic field. Fig.4 shows measured temperature profiles at T1-T3. The self-magnetic field of the 2nd GdBCO wire was a maximum when 6 J was applied for 2 s with single heater and 5 J was applied for 2 s with two heaters. The heat which was applied by single heater is cooled by liquid nitrogen. In this case, part of the current flows to the stabilizer of the 1st GdBCO wire. But, the current is enough bypassed when 5 J was applied for 2 s with two heaters.
-2 -4 -6
0.000 8
10
12
14
-2 -4
V1-2 V2-3 V3-4 V1-4
0.005
-6 -8 -10
0.000
-8 18
16
0
8
10
12
Time (s)
14
12
12
T1 T2 T3
6 4 2
(b)
heater
86 10
84
8
82 80 78
86 84
8 82
T1 T2 T3
6 4
80
2
0
-12 18
16
(a)
heater 10
Voltage (V)
V1-2 V2-3 V3-4 V1-4
Voltage (V)
Voltage (V)
0.005
2
Self-magnetic field
78
Temperature (K)
0
4
(b)
Temperature (K)
2
heater (1/10 scale) 0.010
Magnetic flux density (G)
4
Magnetic flux density (G)
(a)
Self-magnetic field
Voltage (V)
6
heater (1/10 scale)
0.010
0
8
10
Time (s)
12
14
16
18
20
22
24
26
76 28
10
Time (s)
Fig. 3. Generated the voltages along the each point (V1-2-V3-4) and end-to-end (V1-4), and the 1/10 scaled heater input and self-magnetic field measured by Hall sensor attached on 2nd GdBCO wire (a) when 6 J was applied for 2 s with single heater; (b) when 5 J was applied for 2 s with two heaters.
76 30
20
Time (s)
Fig. 4. Measured temperature profiles at T1-T3 (a) when 6 J was applied for 2 s with single heater; (b) when 5 J was applied for 2 s with two heaters.
3.2. Double pulse heating Fig.5 shows the generated voltage traces, and the 1/10 scaled heat input and measured self-magnetic field. Fig.6 shows measured temperature profiles. Self-magnetic field of the 2nd GdBCO wire was a maximum when 5 J was applied twice by single heater for 1 s with 2 s intervals and twice by two heaters for 2 s with 4 s intervals. The second half of the selfmagnetic field is getting stronger than the first half of it in Fig.5. The method of double pulse heating is the useful because the temperature is elevated in the second half in Fig.6.
-2 -4 -6 -8 -10
0.000 8
10
12
14
16
18
Time (s)
20
22
-12 24
4 2 0 -2
0.005
V1-2 V2-3 V3-4 V1-4
-4 -6 -8 -10
0.000 8
10
12
14
16
18
20
22
24
-12 26
Time (s)
Fig. 5. Generated the voltages along the each point (V1-2-V3-4) and end-to-end (V1-4), and the 1/10 scaled heater input and self-magnetic field measured by Hall sensor attached on 2nd GdBCO wire when 5 J was applied (a) twice by single heater for 1 s with 2 s intervals; (b) twice by two heaters for 2 s with 4 s intervals.
12
(a)
heater 10
90
12
88
10
86
8 T1 T2 T3
6 4
84 82 80
2
78
0 10
20
Time (s)
30
76
(b)
heater
86 84
8
Voltage (V)
V1-2 V2-3 V3-4 V1-4
0.004
Self-magnetic field
Voltage (V)
0
(b)
heater (1/10 scale) 0.010
T1 T2 T3
6 4 2
82 80 78
Temperature (K)
2
Voltage (V)
4
Temperature (K)
Voltage (V)
6
Magnetic flux density (G)
(a) Self-magnetic field
Magnetic flux density (G)
heater (1/10 scale) 0.008
0 10
20
30
76
Time (s)
Fig. 6. Measured temperature profiles at T1-T3 when 5 J was applied (a) twice by single heater for 1 s with 2 s intervals; (b) twice by two heaters for 2 s with 4 s intervals.
152
S.B. Kim et al. / Physics Procedia 65 (2015) 149 – 152
3.3. The current bypassing value in each self-magnetic field Fig.7 shows the measured self-magnetic field when the current of up to 100 A was transported with sweep rate of 3.257 A/s. The self-magnetic field is 10.5 G when a current of 100 A was transported in the 2nd GdBCO wire. So, selfmagnetic field is 0.104 G per 1 A. Thus, the current bypassing value when 6 J was applied for 2 s with single heater was 62 A, when 5 J was applied for 2 s with two heaters was 90 A, when 5 J was applied twice by single heater for 1 s with 2 s intervals was 89 A and when 5 J was applied twice by two heaters for 2 s with 4 s intervals was 90 A. All of the current was not bypassed, because the GdBCO wire have stabilizer. We considered that the current was transpored a layer of stabilizer. 120 Current
18
100
16 14
80
12 10
60
8
40
6 4
Generated magnetic field
2 0
8
12
16
20
24
28
32
36
40
44
20
Transport current (A)
Magnetic flux density (G)
20
0
Time (s)
Fig. 7. Measured self-magnetic field when the current of up to 100 A was transported with sweep rate of 3.257 A/s.
4. Results and discussion (superconducting joint wire) 4.1. Single pulse heating Fig.8 shows the measured self-magnetic field when the current of up to 10 A was transported with sweep rate of 3.257 A/s in joint part and no joint part. Fig.9 shows the 1/10 scaled heater input and self-magnetic field measured by Hall sensor attached on GdBCO wire when 2 J was applied. The self-magnetic field was increased linearly when the current of up to 10 A was transported. So, it is possible to convert the self-magnetic field into current value. In GdBCO loopshaped test coil with superconducting joint, there are no difference of current bypassing properties between single and two heaters input when the input heating is 2J. In the case of GdBCO wire without stabilizer, the thermal diffusion along the longitudinal direction is very low, and inputted heat contributes to raising the local temperature in the wire.
0.0004 2 0
Self-magnetic field 0
10
20
Time (s)
30
0.0000 40
6 0.0008 4
Self-magnetic field
2
0.0004 0.0000
0 0
5
0.008
0.006
-2
10
15
20
25
30
35
Time (s)
Fig. 8. Measured self-magnetic field when the current of up to 10 A was transported with sweeprate of 3.257 A/s (a) joint part; (b) no joint part.㻌
No joint part
0.004
-4 -6
0.002
(a)
Voltage (V)
Current (A)
4
0.0012
heater (1/10 scale)
0 -2
0.006
No joint part
0.004
-4 -6
0.002
(b)
-8
0.000
2
Joint part
Current (A)
0.0008
Operating current
Joint part
Current (A)
0.0012
6
0.010
0
heater (1/10 scale)
0.0016
Voltage (mV)
Current (A)
8
Operating current
Voltage (V)
8
2
0.008
0.010
(b)
10
0.0016
Voltage (V)
0.0020
(a)
10
-8
0.000 0
5
10
15
Time (s)
20
-10 25
0
5
10
15
20
-10 25
Time (s)
Fig. 9. The 1/10 scaled heater input and self-magnetic field measured by Hall sensor attached on GdBCO wire when 2 J was applied (a) by single heater for 1 s; (b) by two heaters for 1 s.
5. Conclusion The self-magnetic field by transported current was measured as function of number of heat input and duration time of heating by heater. Then, the current bypassing properties in 2G wire loop circuits with/without superconducting joint were evaluated using converted bypassing current from measured self-magnetic field. In test coil with normal joint by soldering, the whole transport current of 90 A was bypassed by 5J heat input. In GdBCO loop-shaped test coil with superconducting joint, there are no difference of current bypassing properties between single and two heaters input when the input heating is 2J. In the case of GdBCO wire without stabilizer, the thermal diffusion along the longitudinal direction is very low, and inputted heat contributes to raising the local temperature in the wire. Therefore, in the 2G wires without stabilizer, it becomes possible to bypassing the current using the single heater. References [1] Yeonjoo Park, Hyun-Jin Shin,Young-Gyun Kim, Young Kun Oh, and Haigun Lee, IEEE Trans, Appl. Supercond. 23 (2013) 6600804
ScienceDirect Physics Procedia 65 (2015) 149 – 152
27th International Symposium on Superconductivity, ISS 2014
Current bypassing properties by thermal switch for PCS application on NMR/MRI HTS magnets S.B. Kima,*, M. Takahashia, R. Saitoa, Y.J. Parkb, M.W. Leeb, Y.K. Ohb, H.S. Annb a
Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka , Kita-ku , Okayama 700-8530, JAPAN b K·Joins, Inc. 913C H-1 KIST Venture Town Hwarangro 14 gil 5, Seongbuk-gu, Seoul 136-791, KOREA
Abstract We develop the compact NMR/MRI device using high temperature superconducting (HTS) wires with the persistent current mode operating. So, the joint techniques between 2G wires are very important issue and many studies have been carried out. Recently, the K·JOINS, Inc. has developed successfully the high performance superconducting joints between 2G wires by partial melting diffusion and oxygenation annealing process [1]. In this study, the current bypassing properties in a loop-shaped 2G wire are measured experimentally to develop the permanent current switch (PSC). The current bypassing properties of loop-shaped test coil wound with 2G wire (GdBCO) are evaluated by measured the self-magnetic field due to bypassed current by Hall sensors. The strain gauge was used as heater for persistent current switch, and thermal properties against various thermal inputs were investigated experimentally. © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-reviewunder underresponsibility responsibility of the Program Committee. Peer-review of the ISSISS 20142014 Program Committee Keywords:NMR relaxometry; HTS coil magnet; joints between 2G wires; persistent current switch (PCS); permanent current mode
1. Introduction The low temperature superconducting (LTS) coils are used in present NMR / MRI devices and liquid helium is used for their cooling. However, it is possible to reduce the operating costs by manufacturing the superconducting magnet which is consisted of the high temperature superconducting (HTS) coil using liquid nitrogen cooling. We develop the compact NMR/MRI device using HTS wires with the persistent current mode operating. So, the joint techniques between HTS wires are very important issue and many studies have been carried out. Recently, the K·JOINS, Inc. has developed successfully the high performance superconducting joints between 2G wires by partial melting diffusion and oxygenation annealing process [1]. In general, the thermal heaters are usually used for persistent current switch (PCS), and the superconducting region turn into the normal state by a heater. In this study, the current bypassing properties in a loopshaped 2G wire are measured experimentally to develop the PCS The current bypassing properties of loop-shaped test coil wound with 2G wire (GdBCO) are evaluated by measured the self-magnetic field due to bypassed current by Hall sensors. The strain gauge was used as heater for persistent current switch, and thermal properties against various thermal inputs were investigated experimentally.
*Corresponding author. Tel.: +81-86-251-8116; fax: +81-86-251-8110. E-mail address: [email protected]
1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the ISS 2014 Program Committee doi:10.1016/j.phpro.2015.05.088
150
S.B. Kim et al. / Physics Procedia 65 (2015) 149 – 152
2. Experimental details Fig.1 shows the (a) schematic drawing of the proposed compact NMR magnet using the high performance superconducting joints and (b) photograph of the loop-shaped test coil with high performance superconducting joints between 2G (GdBCO) wires by partial melting diffusion and oxygenation annealing process. The proposed NMR superconducting magnet wound with 2G wires to be operating in the persistent current mode. The one layer test coil wound with GdBCO wire without stabilizer is prepared to study the PCS as shown in Fig. (b). A superconducting joint in Fig.1 (b) is prepared by K·JOINS, Inc.. It is necessary to install a PCS in NMR/MRI HTS magnets operating in persistent current mode. The current bypassing properties are determined by PCS. Fig.2 shows the schematic view of the test coils wound with GdBCO wire (a) with normal joint by soldering and (b) GdBCO loop-shaped test coil with superconducting joint. In test coil with normal joint by soldering, the thermal couples and voltage taps are attached to measure the current bypassing properties. The interval among T1, T2 and T3 is 2 cm (Fig.2 (a)). The intervals between V1 and V2, V2 and V3, and V3 and V4 are 32 cm, 1.5 cm and 2 cm respectively (Fig.2 (a)). In both test coils, the two heaters (strain gauge) and the Hall sensors are attached to measure the current bypassing properties. Table 1 shows specifications of GdBCO 2G wire and heater. Table 2 shows applied thermal heat by the heater. In test coils with normal joint and superconducting joint, the currents of 100 A and 10 A are transported respectively because the critical current at superconducting joint is 17 A. The current bypassing properties of loop-shaped test coils wound with 2G wire (GdBCO) are evaluated by measured the self-magnetic field due to bypassed current by Hall sensors. Filler Caps
Double pancake coil
Level Sensor
PCS
+
Heater
I
(b)
Superconducting joint
(a)
䠉 DC power supply
Probe Assembly
Liquid Nitrogen Bath
Superconducting joint part
Super-conducting Coil
Fig. 1. (a) Schematic drawing of the proposed compact NMR magnet using the high performance superconducting joints; (b) photograph of the loop-shaped test coil with high performance superconducting joints between 2G (GdBCO) wires by partial melting diffusion and oxygenation annealing process. 1st GdBCO wire
T1
T3
V2
V3
V4
V1
(a) 䞉䞉䞉Voltage tap
1&2
Normal joint Current part lead
3&4
T2
V2 6.2 cm V3
Superconducting joint part
V1 24.8 cm
Current lead V4
(b) 䞉䞉䞉Voltage tap 䞉䞉䞉Hall sensor 䞉䞉䞉 Heater Fig. 2. The schematic view of the test coils wound with GdBCO wire (a) with normal joint by soldering and (b) GdBCO loop-shaped test coil with superconducting joint. 䞉䞉䞉Thermocouple
䞉䞉䞉 Heater
䞉䞉䞉Hall sensor
Table 1. Specifications of GdBCO 2G wire and heater Components Parameters GdBCO conductor (Ag/GdBCO/Buffer/Substrate/Ag)
Heater (Strain gauge)
Specification
Critical current at 77K Length Width Thickness Thickness of upper Ag layer Thickness of GdBCO layer Thickness of buffer layer Thickness of substrate Thickness of bottom Ag layer
114 A 100, 105 mm 4 mm 55 μm 2 μm 1 μm 㹼0.2 μm 50 μm
Thickness Length Width Resistance
50 μm 11 mm 5 mm 1000 :
1.8 μm
151
S.B. Kim et al. / Physics Procedia 65 (2015) 149 – 152 Table 2. Applied thermal heat by the heater The number of times of supply
The number of heaters
Times [s]
Loading interval [s]
Joule heating [J]
Once
1
0.5 1* 2 0.5 1* 2
-
1-5 1-5 1-6 1-5 1-6 1-5 5 5 5 5 5 5
2
Twice
1
0.5 2,4 1 2,4 2 2,4 2 0.5 2,4 1 2,4 2 2,4,6 * Applied various input heating for superconducting joint wire
3. Results and discussion (normal joint wire) 3.1. Single pulse heating Fig.3 shows the generated voltage traces, and the 1/10 scaled heat input and measured self-magnetic field. Fig.4 shows measured temperature profiles at T1-T3. The self-magnetic field of the 2nd GdBCO wire was a maximum when 6 J was applied for 2 s with single heater and 5 J was applied for 2 s with two heaters. The heat which was applied by single heater is cooled by liquid nitrogen. In this case, part of the current flows to the stabilizer of the 1st GdBCO wire. But, the current is enough bypassed when 5 J was applied for 2 s with two heaters.
-2 -4 -6
0.000 8
10
12
14
-2 -4
V1-2 V2-3 V3-4 V1-4
0.005
-6 -8 -10
0.000
-8 18
16
0
8
10
12
Time (s)
14
12
12
T1 T2 T3
6 4 2
(b)
heater
86 10
84
8
82 80 78
86 84
8 82
T1 T2 T3
6 4
80
2
0
-12 18
16
(a)
heater 10
Voltage (V)
V1-2 V2-3 V3-4 V1-4
Voltage (V)
Voltage (V)
0.005
2
Self-magnetic field
78
Temperature (K)
0
4
(b)
Temperature (K)
2
heater (1/10 scale) 0.010
Magnetic flux density (G)
4
Magnetic flux density (G)
(a)
Self-magnetic field
Voltage (V)
6
heater (1/10 scale)
0.010
0
8
10
Time (s)
12
14
16
18
20
22
24
26
76 28
10
Time (s)
Fig. 3. Generated the voltages along the each point (V1-2-V3-4) and end-to-end (V1-4), and the 1/10 scaled heater input and self-magnetic field measured by Hall sensor attached on 2nd GdBCO wire (a) when 6 J was applied for 2 s with single heater; (b) when 5 J was applied for 2 s with two heaters.
76 30
20
Time (s)
Fig. 4. Measured temperature profiles at T1-T3 (a) when 6 J was applied for 2 s with single heater; (b) when 5 J was applied for 2 s with two heaters.
3.2. Double pulse heating Fig.5 shows the generated voltage traces, and the 1/10 scaled heat input and measured self-magnetic field. Fig.6 shows measured temperature profiles. Self-magnetic field of the 2nd GdBCO wire was a maximum when 5 J was applied twice by single heater for 1 s with 2 s intervals and twice by two heaters for 2 s with 4 s intervals. The second half of the selfmagnetic field is getting stronger than the first half of it in Fig.5. The method of double pulse heating is the useful because the temperature is elevated in the second half in Fig.6.
-2 -4 -6 -8 -10
0.000 8
10
12
14
16
18
Time (s)
20
22
-12 24
4 2 0 -2
0.005
V1-2 V2-3 V3-4 V1-4
-4 -6 -8 -10
0.000 8
10
12
14
16
18
20
22
24
-12 26
Time (s)
Fig. 5. Generated the voltages along the each point (V1-2-V3-4) and end-to-end (V1-4), and the 1/10 scaled heater input and self-magnetic field measured by Hall sensor attached on 2nd GdBCO wire when 5 J was applied (a) twice by single heater for 1 s with 2 s intervals; (b) twice by two heaters for 2 s with 4 s intervals.
12
(a)
heater 10
90
12
88
10
86
8 T1 T2 T3
6 4
84 82 80
2
78
0 10
20
Time (s)
30
76
(b)
heater
86 84
8
Voltage (V)
V1-2 V2-3 V3-4 V1-4
0.004
Self-magnetic field
Voltage (V)
0
(b)
heater (1/10 scale) 0.010
T1 T2 T3
6 4 2
82 80 78
Temperature (K)
2
Voltage (V)
4
Temperature (K)
Voltage (V)
6
Magnetic flux density (G)
(a) Self-magnetic field
Magnetic flux density (G)
heater (1/10 scale) 0.008
0 10
20
30
76
Time (s)
Fig. 6. Measured temperature profiles at T1-T3 when 5 J was applied (a) twice by single heater for 1 s with 2 s intervals; (b) twice by two heaters for 2 s with 4 s intervals.
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S.B. Kim et al. / Physics Procedia 65 (2015) 149 – 152
3.3. The current bypassing value in each self-magnetic field Fig.7 shows the measured self-magnetic field when the current of up to 100 A was transported with sweep rate of 3.257 A/s. The self-magnetic field is 10.5 G when a current of 100 A was transported in the 2nd GdBCO wire. So, selfmagnetic field is 0.104 G per 1 A. Thus, the current bypassing value when 6 J was applied for 2 s with single heater was 62 A, when 5 J was applied for 2 s with two heaters was 90 A, when 5 J was applied twice by single heater for 1 s with 2 s intervals was 89 A and when 5 J was applied twice by two heaters for 2 s with 4 s intervals was 90 A. All of the current was not bypassed, because the GdBCO wire have stabilizer. We considered that the current was transpored a layer of stabilizer. 120 Current
18
100
16 14
80
12 10
60
8
40
6 4
Generated magnetic field
2 0
8
12
16
20
24
28
32
36
40
44
20
Transport current (A)
Magnetic flux density (G)
20
0
Time (s)
Fig. 7. Measured self-magnetic field when the current of up to 100 A was transported with sweep rate of 3.257 A/s.
4. Results and discussion (superconducting joint wire) 4.1. Single pulse heating Fig.8 shows the measured self-magnetic field when the current of up to 10 A was transported with sweep rate of 3.257 A/s in joint part and no joint part. Fig.9 shows the 1/10 scaled heater input and self-magnetic field measured by Hall sensor attached on GdBCO wire when 2 J was applied. The self-magnetic field was increased linearly when the current of up to 10 A was transported. So, it is possible to convert the self-magnetic field into current value. In GdBCO loopshaped test coil with superconducting joint, there are no difference of current bypassing properties between single and two heaters input when the input heating is 2J. In the case of GdBCO wire without stabilizer, the thermal diffusion along the longitudinal direction is very low, and inputted heat contributes to raising the local temperature in the wire.
0.0004 2 0
Self-magnetic field 0
10
20
Time (s)
30
0.0000 40
6 0.0008 4
Self-magnetic field
2
0.0004 0.0000
0 0
5
0.008
0.006
-2
10
15
20
25
30
35
Time (s)
Fig. 8. Measured self-magnetic field when the current of up to 10 A was transported with sweeprate of 3.257 A/s (a) joint part; (b) no joint part.㻌
No joint part
0.004
-4 -6
0.002
(a)
Voltage (V)
Current (A)
4
0.0012
heater (1/10 scale)
0 -2
0.006
No joint part
0.004
-4 -6
0.002
(b)
-8
0.000
2
Joint part
Current (A)
0.0008
Operating current
Joint part
Current (A)
0.0012
6
0.010
0
heater (1/10 scale)
0.0016
Voltage (mV)
Current (A)
8
Operating current
Voltage (V)
8
2
0.008
0.010
(b)
10
0.0016
Voltage (V)
0.0020
(a)
10
-8
0.000 0
5
10
15
Time (s)
20
-10 25
0
5
10
15
20
-10 25
Time (s)
Fig. 9. The 1/10 scaled heater input and self-magnetic field measured by Hall sensor attached on GdBCO wire when 2 J was applied (a) by single heater for 1 s; (b) by two heaters for 1 s.
5. Conclusion The self-magnetic field by transported current was measured as function of number of heat input and duration time of heating by heater. Then, the current bypassing properties in 2G wire loop circuits with/without superconducting joint were evaluated using converted bypassing current from measured self-magnetic field. In test coil with normal joint by soldering, the whole transport current of 90 A was bypassed by 5J heat input. In GdBCO loop-shaped test coil with superconducting joint, there are no difference of current bypassing properties between single and two heaters input when the input heating is 2J. In the case of GdBCO wire without stabilizer, the thermal diffusion along the longitudinal direction is very low, and inputted heat contributes to raising the local temperature in the wire. Therefore, in the 2G wires without stabilizer, it becomes possible to bypassing the current using the single heater. References [1] Yeonjoo Park, Hyun-Jin Shin,Young-Gyun Kim, Young Kun Oh, and Haigun Lee, IEEE Trans, Appl. Supercond. 23 (2013) 6600804