SI-7
ITER超伝導導体の技術課題と取り組み
Technical problem and resolution of superconductor for the ITER magnet
布谷嘉彦, 名原 啓博, 高橋良和, 押切雅幸, 堤 史明, 高村 淳, 中瓶子 伸二, 渋谷 和之
Y.Nunoya, Y.Nabara, Y.Takahashi, M.Oshikiri, F.Tsutsumi, J.Takamura, S.Chuheishi, K.Shibutani
日本原子力研究開発機構
Japan Atomic Energy Agency
Introduction
Japan Atomic Energy Agency (JAEA) isresponsible for Nb3Sn Cable-in-Conduit conductors(CICC) for the Central Solenoid (CS) and the
Toroidal Field (TF) coil under the ITER project [1].
The CS conductor consists of 576 Nb 3Sn and 288Cu strands which are cabled in five stages aroundthe central spiral and then wrapped with stainlesssteel tape as shown in Fig.1 [2][3].
Full-size conductor test was performed to confirm
performance using SULTAN facility at Switzerland,

Fig. 1. Nb3Sn cable-in-conduit type conductor for ITER CS
conductor consists of 576 Nb3Sn and 288 Cu strands. Outerdimension of jacket is 49 m

especially effect of electromagnetic load cycles on
the current sharing temperature (Tcs), because CS
is operated in pulse mode.
The original (reference) conductor which had
relatively long twist pitch cabling design is called
as the normal twist pitch (NTP) conductor. NTP
conductor showed Tcs decrease with increasing thenumber of cycles as shown in Fig.2 with thenotation “conductor C NTP”.
The destructive examination was performed on thesample after the cyclic test [4]. The photographs ofthe cable and the conductor cross section are shownin Fig.3. There observed strand deformation likebucking at the low transverse load side (“B” in thefigure), where no deformation at the high transverse
load side (“A” in the figure) was observed. Due tothe electromagnetic load, the cable was moved
toward “A” side, resulting in the void in “B” side.
Consequently, the buckling of the strand wasoccurred by an axial compressive force that wasinduced by the difference of thermal expansion
between strand and stainless steel jacket, because
the supporting and the friction of the jacket and thecable on the strand changes by the induced void andthen strand deformation was developing as
increasing the number of cycles. This phenomena
was also observed in TF conductors sample,
however it was not so dominant because of therequired number of cycles is much less (< 1000).
Cable Optimization
Although it is not clear whether the Tcs decrease

Fig. 2 Current sharing temperature vs. electromagnetic load cyclesof full-size conductor samples, measured at experimental facility(SULTAN). Twist pitch sequence STP: 20-45-80-150-450 mm,
NTP: 45-85-125-250-450 mm.

Fig. 3 Strand deformation and location dependence in theconductor cross section.

could happen in ITER CS, because SULTAN
sample does not have the same environment
condition such as field distribution along conductor
length, conductor shape where SULTAN sample isstraight and short, and so on. However in order toeliminate concern that this could happen to theITER CS, cable optimization was planned in theview that improve of cable stiffness could result inregistration of strand buckling. Therefore, the shorttwist pitch (STP) conductor was introduced.
Twist pitch sequence of both STP and NTP arelisted in Table I. The twist pitch of STP conductor
at the first stage that composed of a triplet cable isConclusion
By introducing short twist pitch conductor,performance during electromagnetic cycles wasimproved and concern of Tcs decrease in ITER CS
is eliminated. Improvement is understood thatshorting pitch of the triplet in the first stage makemore engagement of strand providing more
stiffness of the cable that prevent strand
deformation like buckling observed in thedestructive examination of the previous SULTAN
sampleReference[1]

Table I

Twist pitch of cables for CS conductors
Twist pitch [mm]

Items

[2]
STP

NTP
Cond. C

Cond. A

Cond. B

45

23

20

2nd stage

85

48

45

3rd stage

125

88

80

4th stage

250

155

150

5th stage

450

452

450

1st stage

about half, assuming the triplet is most effective
component that may change cable stiffness.
Test Result
Tcs of the STP conductor was tested at SULTAN
facility and showed no Tcs decrease during
electromagnetic cycles and warm up & cool down
as shown in Fig 3 (Conductor A and B). It is
understood that the triplet with a shorter twist pitch
has better engagement among strands producing
more stiffness resulting in less deformation ofstrand in “B” side. This result is acceptable for CS
conductors.

[3]

[4]

N. Mitchell, et al., “The ITER Magnets: Design and Construction
Status,” IEEE Trans. Appl. Supercond., vol. 22, 4200809 (9pp),
2012.
A. Devred, et al., “Status of ITER Conductor Development andProduction,” IEEE Trans. Appl. Supercond., vol. 22, 4804909 (9pp),
2012.
K. Hamada, et al., “Preparation for the ITER Central Solenoid
Conductor Manufacturing”, IEEE Trans. Appl. Supercond., vol. 22,4203404 (4pp), 2012.
T. Hemmi, et al., “Test Results and Investigation of Tcs
Degradation in Japanese ITER CS Conductor Samples”, IEEE
Trans. Appl. Supercond., vol. 22,4803305 (4pp), 2012.