高温超伝導WISE導体の高磁場試験における電流導入部の振る舞いについて

8P12 Behavior of Current lead structure in High-Temperature Superconducting WISE
Conductors under High-Field Tests
成嶋吉朗、柳長門、宮澤順一
NARUSHIMA Yoshiro1,2), YANAGI Nagato1,2), MIYAZAWA Junichi1,2)
核融合研、2)総研大
1)
NIFS, 2)SOKENDAI

1)

V[mV]

Fig.2 (a) End of the WISE-U conductor removed from thecurrent feeder. HTS tapes on the anode side (left) remain, but
B=5T
those on T=30K,
the cathodeside (right)#0040
are burned and cut. (b)Aluminum pipe on the cathode side. The notch can be seenindicated by arrows.

r[n]

For constructing magnets for the next-generation fusion devices,
the HTS (high-temperature superconducting) conductor is a feasible
candidate because of its higher critical current in a high magnetic
field in comparison to LTS (low-temperature superconducting)conductors. Various types of HTS conductors have been fabricatedand studied in NIFS (National Institute for Fusion Science). The
WISE (Wound and Impregnated Stacked Elastic tapes) conductor [1]is made by winding laminated HTS tape wires into a specified coilshape, etc., and then impregnating, and fixing the wires with lowmelting-point metal. Before impregnation, the stacked HTS tapewires are free to move, enabling strain-free winding [2] and flexible
coil construction. The purpose of this study is to clarify the currentcarrying properties of this WISE conductor in a magnetic field. As
shown in Figure 1, a U-shaped WISE conductor with a length of 2m was fabricated by connecting an HTS tape contained inside analuminum pipe to an oxygen-free copper current feeder. A criticalcurrent Ic = 10.8 kA @ 40 K, 5 T was obtained [3, 4]. On the otherhand, at T = 30 K, a maximum current value of 16.9 kA was recorded
at B = 5 T. Before reaching the critical current value, the HTS tapesin the current feeder were burned out. Figure 2(a) shows theconductor part of the WISE-U conductor removed from the current
feeder after the current test. The HTS tape on the left side (anode)remained, but that on the right side (cathode) was burned or cut off.
Notches were found on the edge of the aluminum pipe, likely due tocurrent flow (Fig. 2(b)). The voltage at the current feeder before thequench is shown in Fig. 3(a). On the anode (black), the voltage
increases linearly with increasing current, while on the cathode (red),the voltage increases nonlinearly. Therefore, for Ips < 12.3 kA, thevoltage on the cathode is lower than that of anode, while for Ips >12.3 kA, vice versa. The average resistance on the anode is about 32n, while that on the cathode increases with current, reaching 51 n
at Ips = 16.6 kA as shown in Fig.3 (c). The linearity in anode voltageindicates normal conductivity. Non-linearity of the cathode suggests
current-dependent degradation. Figure 3 (b, d) shows that the sharp
increase in voltage and resistance at Ips = 16.6 kA indicates that theHTS tape burned out at this time; for Ips > 16.6 kA, the anode voltage
and resistance do not change, while the cathode ones increase
sharply. Since the resistance increases when superconductivity isdestroyed, it can be inferred that the HTS tape is being destroyed.
The current feeder was connected to an oxygen-free copper current
terminal and REBCO tape by low-melting-point metal impregnation.
The current feeder was not sufficiently fixed to the aluminum pipe,and distortion during the manufacturing process was thought to be
the cause of the burnout in the current introduction part.

1.0(a)

Cathode

0.5
080
60
40
200(b)

Anode

Anode
Cathode(c)(d)
Cathode
Anode
Anode

Cathode0 2 4 6 8 10121416
Ips[kA]

16.0

16.5

17.0

Ips[kA]

Fig.3 (a) (b) Voltage V and (c) (d) resistance r of current leadagainst the supply current. (a) (c) before quench. (b) (d)during quench.

This study is supported by NIFS UFZG-003 and UFZG-009
1. J. Miyazawa, et. al. Japanese published examined patentapplication No.6749541
2. N. Narushima, et al. PFR, Vol. 15 (2020) 1405076
3. N. Narushima, et al. Abstracts of CSSJ Conference, Vol. 103(2022) p.115
4. N. Narushima, et al. PFR, Vol. 17 (2022) 2405006

Fig.1 Overview of WISE-U conductor