22P166-P
Neutron Irradiation Effect on Superconducting Magnet Materials
超伝導マグネット材料の中性子照射効果
Arata Nishimura1, Takao Takeuchi2, Shigehiro Nishijima3, Gen Nishijima2, Yoshinobu Izumi4,
Masahiro Imaizumi5, Tsutomu Hemmi6, Kentaro Ochiai6, Hidetoshi Oguro7, Kazuo Watanabe7,
Masanori Yamasaki7 and Tatsuo Shikama7
1
西村 新 , 竹内孝夫2, 西嶋茂宏3, 西島 元2, 泉 佳伸4, 今泉雅裕5, 辺見 努6,
落合謙太郎6, 小黒英俊7, 渡辺和雄7, 山崎正徳7, 四竃樹男7
1

National Institute for Fusion Science322-6, Oroshi, Toki, Gifu 509-5292, Japan
核融合科学研究所 〒509-5292 土岐市下石町322-6
2National Institute for Materials Science
1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
物質材料研究機構 〒305-0047 つくば市千現1-2-1
3Osaka University
2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
大阪大学 〒565-0871 吹田市山田丘2-1
4University of Fukui
3-9-1 Bunkyo, Fukui, Fukui, 910-8507, Japan
福井大学 〒910-8507 福井市文京3-9-1
5Nipponn kayaku Co., Ltd.
3-31-12 Shimo, Kitaku, Tokyo, 115-8588 Japan
日本化薬(株) 〒115-8588 東京都北区志茂3-31-12
6

Japanapan Atomic Energy Agency
2-4 Shirakata Shirane, Tokai, Naka, Ibaraki 319-1195, Japan
日本原子力研究開発機構 〒319-1195 那珂市東海白方白根2-4
7Tohoku University
2-1-1 Katahira, Aoba, Sendai, Miyagi 980-8577, Japan
東北大学 〒980-8577 仙台市青葉区片平2-1-1
A fusion reactor will generate 14 MeV neutrons after Deuterium-Tritium fusion reaction. The neutron willreach superconducting magnet and activate superconducting strand and insulation materials. The change insuperconducting properties was studied and the radiation effect on interlaminar shear strength of insulation
composite was investigated. Also, an effort to install 15.5 T superconducting magnet and a variabletemperature insert was succeeded at Oarai center in Tohoku University and the commissioning isundergoing. This paper reports some topical results on the neutron irradiation effect on the superconducting
strand and the composite with cyanate ester – epoxy bended resin and the status of the new systems.

1. Introduction
To study the mechanism of neutron irradiation
effect on superconductivity of Nb3Sn strand andto construct a database for a design and aconstruction of fusion magnets, irradiation tests
were carried out using a fission reactor and 14
MeV neutron facility. In parallel with irradiationon the Nb3Sn strand, a study on interlaminarshear strength (ILSS) of a composite withpolyimide films, glass clothes and cyanate ester –epoxy blended resin was performed. Since thesamples were activated by the irradiation, all tests
after irradiation were carried out in a radiation
control area in Tohoku University and Japan
Atomic Energy Agency (JAEA). To carry out thesuperconducting tests with activated ones in highmagnetic field, a new test facility consists of 15.5
T superconducting magnet and a variabletemperature insert was installed at a radiation
control area in Oarai center, Tohoku University.
This paper will present some topical results andintroduce the new facility.

Critical current (A)2. Neutron Irradiation Effect on Nb3Sn Strand
The Nb3Sn strand with 0.7 mm diameter wasirradiated at 14 MeV neutron source at Fusion
Neutronics Source in JAEA. Then the sample wassent to Tohoku University and the superconducting
properties were measured with 28 T hybrid magnet.
The results of critical current are shown in Fig. 1 asa function of magnetic field. After the irradiation,
the critical current increased especially in the lower
magnetic field. As far as the results obtained, theincrease of the critical current in the higher
magnetic field started after a certain amount of theneutron fluence. It suggests that the flux pinning
force was strengthened by the irradiation and thestrengthening was improved with an increase of theneutron fluence.
200
150

1.78x1021(RT)
2.65x1021(RT)

Non-irrad.

2.65x1021 (RT)
Non-irrad.

3.52x1020(4.5K)

100

1.78x1021 (RT)

Non-irrad.

Nb3Al

1.78x1021 (RT)

50

NbTi

0812

Nb3Sn

162024Magnetic field (T) Border point

3. Irradiation Effect on Composite Material
The blended resin with cyanate ester and epoxy
was used for fabrication of the composite withpolyimide film and glass cloth. The blended ratio
was changed and the samples were irradiated at
JRR-3 (fission reactor). After the irradiation, theILSS was measured at 77 K in the radiation control
area at Oarai center. The results are shown in Fig. 2.
Since the gamma ray irradiation is very hard in
JRR-3 (2.5 MGy/hr), the data were plotted against
gamma ray dose. In Fig. 2, CTD and MCE mean acyanate ester resin and EP presents epoxy resin.
EP+D230 means a 100% epoxy resin with hardenerof D230 and it is a reference data. The initial ILSS
is affected by the ratio and the composite withlower ratio showed lower ILSS. The reason is clear,because of luck of the hardener for epoxy resin. Thesamples with 100% cyanate ester resin endured
about 500 MGy although all other samples dropped.
4. A New Superconducting Facility
15.5T superconducting magnet with a RT bore of52 mm diameter was installed together with ashielding structure. It is a conduction cooling typemagnet with GM refrigeration and no use of liquid
helium or liquid nitrogen. The insert was designed
for the magnet and has a capacity of sample currentof 500A and sample temperature of 4.2 K to over
20 K. The magnet can be cooled down in four days
and the sample in the insert can be cooled down in
about four hours. The dependence of the criticalmagnetic field on the sample temperature with thesample irradiated to 1.0 x 1022 n/m2 was evaluated.

Fig. 1 Change in critical current against magnetic field
after 14 MeV neutron irradiation

ILSS (MPa)8070

CTD: 100 for JRR-3 Co-60 irrad.
irradiation

60

CTD: 100

JRR-3 irrad.
(1.0x1022)(n/m2)

50
40
30
20
10

CTD/EP: 40/60
MCE/EP: 30/70
CTD/EP: 20/80

77 K

EP+D230(1.0x1021)(n/m2)

0Non-irrad.
10-3 10-2 10-1 100 101
Dose (MGy)102 103

Fig. 2 ILSS at 77 K of composites with polyimide film,
glass cloth and blended resin against dose.

Fig. 3 15.5T superconducting magnet (lower) andvariable temperature insert (upper) at Oarai center.