分割型高温超伝導マグネットのための接合抵抗分析研究および照射特性研究の現状
Current status of research of joint resistance analysis and irradiation
characteristics for segmented high-temperature superconducting
magnet8P10

伊藤 悟1，橋爪 秀利1
Satoshi Ito1, Hidetoshi Hashizume1
東北大Tohoku Univ.
11

1. Introduction
Segment-fabricationofhigh-temperature
superconducting magnets has been proposed for large andcomplex fusion magnets using mechanical joint or presswelding of Rare-earth barium copper oxide (REBCO)
tapes with indium [1]. Nondestructive testing of interface
resistance inside REBCO tapes [1–3] has been developed
to analyze joint resistance of the aforementioned joint. For
the discussion of critical current (IC) behavior during
magnet operation and in maintenance, proton irradiation
testing of REBCO tapes was performed at 95–105 K [4].

critical current without proton irradiation). So far, IC of
one REBCO tape sample was measured at 77 K in liquid
nitrogen without returning to RT. IC slightly increased
after returning to RT for the same sample, which indicatesdefect recovery. IC was also measured at various
temperatures and magnetic fields after returning to RT,detail of which is shown in the poster presentation.

2. Interface resistivity evaluation
Interface resistance between REBCO and stabilizers
inside REBCO tape has large impact for joint resistanceand it varies depending on manufacturers and spool batchof REBCO tapes. As a nondestructive testing of theinterface resistance, we have developed a contact-probing
current transfer length method [2]. Interface resistivity(interface resistance for unit area) at 77 K for various
REBCO tapes have been evaluated [1] as well as theirtemperature and magnetic field dependency [3]. Fig. 1
shows an example of interface resistivity of a copper
stabilized REBCO tape as a function of magnetic field at
10 K. The behavior is different from joint resistanceincreasing with an increase in magnetic field. REBCO
property close to the interface might affect the behavior.

3. Irradiation testing
For discussion of IC behavior of REBCO tapes in magnet
maintenance, cryogenic irradiation and IC measurementwith returning to room temperature (RT) are required
whereas IC measurement without returning to RT isneeded for discussion of that during magnet operation. Asa first step, we have prepared proton irradiation stage
cooled with liquid nitrogen, which can keep temperatureof REBCO tapes at 95–105 K. 2.4 MeV proton beam wasirradiated to copper stabilized REBCO tapes, in which
Bragg peak was located at Hastelloy substrate behind
REBCO layer. Fig. 2 shows relationship between DPA
and normalized critical current (= IC/IC0 where IC0 is

Fig. 1 Interface resistivity evaluation of a REBCO tape at 10 K.

Fig. 2 Critical current at 77 K, s.f. as a function of DPA.

References[1] S. Ito et al., Nucl. Fusion, 61 (2021) 115002.
[2] R. Hayasaka et al., IEEE Trans. Appl. Supercond., 29 (2019)
9000805.
[3] Y. Atake et al., MT27 (2021) WED-PO2-613-06.
[4] Y. Ma et al., AESJ Annual Meeting 2022 (2022) 2L13.

Acknowledgement
This work was partially supported by JSPS KAKENHI Grant
Number 20H01884. Measurements under magnetic field werecarried out at the HFLSM, IMR, Tohoku University (Project
Numbers 202012-HMKGE-0202 and 202112-HMKGE-0202).
The proton irradiation was performed at FNL, Tohoku
University.