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

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

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)

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

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

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.

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. MT19 2005 Aim at Jc >2000A/mm2(12T, 4.2K), or even reach to 3000A/mm2

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

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.

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℃.

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.

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.

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

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

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.

Thanks for your attention!