1. Development of Nb3Sn wire for high magnetic field at WST
Xiaguang Sun
June 16, 2015

2. Outline Introduction of WST Performances of sample Main challenges
Main products in WST
Performances of sample
Main challenges
Conclusions

3. WST was founded on February 28, 2003, and the main aim was ITER project.
China undertook:(WST produced all the strands)
180 t NbTi strand: 69% PF, 100% CC and Feeder
30 t Nb3Sn strand: 7% TF
International Thermonuclear Experimental Reactor (ITER)

4. Low Temperature Superconducting Strands for ITER
NbTi
ITER PROJECT
Bronze Nb3Sn
Internal Tin Nb3Sn

5. NbTi/Cu Superconducting Wires for MRI/NMR
Round wires
MRI
NbTi strands for MRI

6. Ic stability of strands designed for ITER project
Ic (4.22 K, 12 T)
IT Nb3Sn strand
Bronze Nb3Sn strand
NbTi strand
All values are larger than the lower ITER limit with good stability.

7. Based on the IT-Nb3Sn/Cu wire for ITER project
Jc as a function of magnetic field
Cross-section of IT Nb3Sn
* S. Hong et al. MT
Aim at Jc >2000A/mm2(12T, 4.2K), or even reach to 3000A/mm2

8. Performances of sample
Jc, non as a function of Nb content
As the Nb content increases:
Jc,non increases；
The difficulty of wire manufacture will be double.
predicted
And a higher Jc was in plan this year, that is Jc>3000A/mm2
Jc non as a function of Nb content

9. Performances of sample
Jc, non as a function of Nb filament size
When the Nb size is 6um, Jc,non reaches the highest value；
When the Nb size is below 2um, the filament breackage may be the main problems.
Jc nonCu as a function of Nb filment size
As the Nb filament size decreases, Jcn firstly increases and then decreases.

10. Performances of sample
F(N) as functions of B(T) with different heat-treatment
1#~6#：Nb/Sn=2.5
3-1#~3-3#：Nb/Sn=2.0
1#~4#：heat-treatment at 660℃
5#： heat-treatment at750 ℃
6#，3-1#~3-3#：heat-treatment at 650℃
F(N) as functions of B(T) at different HT temperature
The better HT temperature is near to 650℃.

11. Performances of sample
RRR value as a function of heat-treatment time
When the heat-treatment temperature is fixed at 650℃
As the time prolong, RRR value decreases;
The time is lower than 20h, Jc is lower than 2000A/mm2.
New design for higher RRR value was in plan this year, that is high Jc with improved RRR.
RRR as a function of heat-treatment time
The better HT time is near to 40h.

12. Performances of sample
The final size of sub-elements 54
sub-elements 84
sub-elements
As the numbers of sub-element increases from 54 to 84,
The final size of sub-element decreases, from ~90um to ~80um;
The breackage increases during wire drawing.
To reduce the sub-element size is in the following work.
To decrease the sub-element size is a big challenge.

13. Performances of sample
Information of the wire
Table of the wire paramater
Items
parameter
Size
Φ0.621～0.81mm
No. of sub-elements 54
No. of Nb filaments in sub-element
324
No. of NbTi filaments in sub-element 18
No. of Nb filaments
342×54=18468
Cu：non-Cu
1.3
Nb filament size
2~5μm
Ic（12T，4.2K）
129～600A
Jcn（12T，4.2K）
2000～2700A/mm2

14. Main challenges already challenges Unit length
>1000m (Jcn<2500A/mm2)
>1000m (Jcn>2500A/mm2)
Jc, non
2000~2700A/mm2
>3000A/mm2
Deff.
70~90um
40~50um
grain size
(after HT)
100~200nm
20~50nm

15. Conclusions
WST succeeded in producing superconducting strands for ITER project with good stability;
Based on producing IT Nb3Sn strand, WST have made a progress on R&D of high Jc Nb3Sn strand；
The development of high field magnet gives us challenges to improve performances of Nb3Sn strand.

16. Thanks for your attention!