THE DEVELOPMENT OF FLEXIBLE SUPERCONDUCTING Nb3Sn BRAIDS AND CABLES

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THE DEVELOPMENT OF FLEXIBLE

SUPERCONDUCTING Nb3Sn BRAIDS AND CABLES

Fang Jun-Ren, Huang Ji-Ming, Li Da-Rong, Shi Feng-Ming, Xiao Ai-Ying, Yi Min-Yu, Hu Qing-Yong, Zhang Yuan-Jin, Yi Zu-Wang

To cite this version:

Fang Jun-Ren, Huang Ji-Ming, Li Da-Rong, Shi Feng-Ming, Xiao Ai-Ying, et al.. THE DEVELOP-

MENT OF FLEXIBLE SUPERCONDUCTING Nb3Sn BRAIDS AND CABLES. Journal de Physique

Colloques, 1984, 45 (C1), pp.C1-417-C1-420. �10.1051/jphyscol:1984185�. �jpa-00223741�

JOURNAL DE PHYSIQUE

Colloque C l , supplément au n° 1, Tome 45, janvier 1984 page Cl-417

THE DEVELOPMENT OF FLEXIBLE SUPERCONDUCTING Nfc>

3

Sn BRAIDS AND CABLES

Fang Jun-ren, Huang Ji-ming, Li Da-rong, Shi Feng-ming, Xiao Ai-ying, Yi Min-yu, Hu Qing-yong, Zhang Yuan-jin and Yi Zu-wang

Changsha Research Institute of Minning & Metallurgy, China

Résume - Des tresses et des câbles multifilamentaires en Nb3 Sn ont été fabriqués par le procédé bronze. Les échantillons longs présentent de bonnes propriétés mécaniques et une capacité rai- sonnable de transport de courant.

Abstract - There have been fabricated flexible superconducting Nb-jSn multifilamentary braids and cables by the bronze process.

Both of braids and cables long samples have a good mechanical property and a reasonable current carrying capacity.

Because the bronze processed Nb3Sn conductors are difficult to be wound into a magnet without-any degradation of superconducting performances due to their embrittlernent, there was developed the

" wind-and-react " technique to avoid the difficulties, by which technique some 12T magnets have been sucessfully fabricated. However, the special requirements in the technique put the researcher and manufacturers of magnet to inconvenience.lt is,therefore, a matter of considerable interest to wind a magnet from the Nb-jSn conductors in as convenient way as from NbTi conductors according to the user's requirements. That is the reason why one is interested in a V-^Ga-NbTi mixed magnet developed by D. Eckert et al./l/ It has been a goal of the present authors to provide researcher and manufacturers for high field magnets with superconducting material that can be conveniently wound into a magnet.

Design and fabrication of conductors

The following principles are used as a guide to the design of multi- filamentary Nb-jSn pre-reacted conductors and the selection of pro- cess parameters: the conductors should have a good mechanical proper-

ty and as high current carrying capacity as possible. It is difficult to combine the requirements in a conductor and in every case they involve trade-offs.

Of the various forms of conductors, the braid and cable are most de- sirable to meet the requirements.

The braids described in this paper consist of 29 strands and 4-6 reinforcing Mo wires; and the cables contain 6 strands cabling round a central Mo(or W) wires (see table l ) . After heat-treatment to form Nb^Sn phase the braids and cables are jjndium plated for the fixture.

Maximum tensile strain was calculated to be 0.8$ in the strands of.

0.14mm diameter of the braids and cables when they were wound round a bobbin of 18mm diameter.

The strands presented here were made by bronze process. It is clear that the performances of such conductors as braids and cables

depend to a great extent on the properties of strands of which the

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984185

C1-418 JOURNAL DE PHYSIQUE

c o n d u c t o r s c o n s i s t . I n t h e o p i n i o n of t h e p r e s e n t a u t h o r s , f o r t h e high p e r f o , m a n c e s s t r a n d s t h e Nb38n phase should have a r e a s o n a b l e volume f r a c t i o n i n t h e s t r a n d s and a s , h i g h d i s p e r s e a s p o s s i b l e o v e r

the m a t r i x , a s w e l l as t h e h i g h q u a l i t y of Nb3Sn; and t h e s t r a n d s should have t h e Nb c o r e u n r e a c t e d . The r e a s o n a b l e volume f r a c t i o n of NbjSn phase i s a t r a d e - o f f between t h e mechanical p r o p e r t i e s and t h e c u r r e n t c a r r y i n g c a p a c i t y ; and t h e h i g h d i s p e r s i o n of Nb3Sn " ^and

" r e t e n s i o n of u n r e a c t e d Nb c o r e a r e employed f o r o b t a i n i n g a good

mechanical p r o p e r t y . The above c o n s i d e r a t i o n s l e a d t o t h e d e s i g n d e t a i l s f o r t h e s t r a n d s a s shown i n t a b l e ( 1 ) and ( 2 ) . A s i l l u s t r a t e d i n t h e n e x t s e c t i o n , t h e b r a i d s and c a b l e s c o n s i s t e d o f t h i s t y p e o f s t r a n d s combine t h e good mechanical p r o p e r t i e s and r e a s o n a b l e c u r r e n t c a r r y i n g c a p a c i t y .

Performance c h a r a c t e r i s t i c s

Performances o f t h e s h o r t samples:

The t y p i c a l v a l u e s of c r i t i c a l c u r r e n t I, a r e a s f o l l o w s ( a t 4.2K 4 ~ ) , b r a i d s - ^{1, =} 900-1100A; c a b l e s - ^{I, =} 180-22OA. 1 , ( 4 ~ ) / I C ( 1 0 T ~ i s a p p r o x i m a t e l y e q u i v a l e n t t o 2.5, t h e d e t e r m i n a t i o n o f t h e comBlete H - ^{I, p l o t i s} u n d e r way. The !PC o f both c o n d u c t o r s a r e s l i g h t l y d i f f e r e n t ( b u t b e i n g of same o r d e r a s 1 7 . 5 ~ ) , depending on t h e h e a t - t r e a t m e n t regime used. The mechanical p r o p e r t i e s i n room t e m p e r a t u r e a r e as follows. A f t e r t h e h e a t - t r e a t m e n t a t 650°C f o r 1 5 h r , t h e b r a i d v ~ i t h s t r a n d s c o n t a i n i n g 301 f i l a m e n t s can 5 e wound round a bobbin o f

1 8 m m d i a m e t e r w i t h o u t t l e g r a d a t i o n of c u r r e n t c a r r y i n g c a p a c i t y and can be r e p e a t e d l y wound round a bobbin of 25mn d i a x e t e r f o r 40 t i m e s w i t h o u t damage. The c a b l e s have a l s o s i n i l a r performance o f bending.

A f t e r , h e a t - t r e a t m e n t a t 650°C f o r 1 5 h r , t h e c a b l e s w i t h a s t r a n d s of 301 f i l a q e n t s have t h e - f a l l o w i n g t e n s i l e p r o p e r t y : = 57 kg/mii2,

60.1 = 41 kg/nn2, & = 1.2%. I t seems t o be c l e a r from t h e d a t a t h a t t h e c a b l e s wound have a good mechanical p r o p e r t y . Although t h e t e n s i l e p r o p e r t i e s of t h e b r a i d s depends t o a e x t e n t on t h e nuinber of r e i n f o r c i n g s t r a n d s t h e y c o n t a i n , t h e i r t e n s i l e ~ r o p e r t y a r e s i m i - l a r t o t h a t f o r c a b l e s .

Performance o f c o i l s :

Typical d a t a o f performarice of c o i l s a r e shown i n t a b l e ( 3 ) . Sofne o f t h e c o i l s have been wound many t i n e s For n o s t o f t h e c o i l s shown t h e t a b l e 3 ) t h e d e g r a d a t i o n of 1, ( compared w i t h s h o r t samples in

i s u s u a l l y l e s s t h a n 105, b u t 20-305 f o r t h e c o i l 8-3 and C-3, due mainly t o t h e o p e r a t i o n and p o s s i b l y e x c e s s i v e number o f f i l a m e n t s i n each s t r a n d o f c o n d u c t o r s . I t i s e v i d e n t from t h e above d a t a t h a t t h e l o n g samples o f t h e b r a i d s and c a b l e s do combine a good mechanical p r o p e r t y and a r e a s o n a b l e c u r r e n t c a r r y i n g c a p a c i t y .

D i s s c u s i o n

A s h a s been p o i n t e d o u t i n t h e d i s s c u s i o n about t h e p r i n c i p l e o f de- s i g n f o r t h e s t r a n d s , t o coxbine a reasonable c u r r e n t c a r r y i n g capa- c i t y and a good mechanical p r o p e r t y t h e Nb3Sn phase i n t h e s t r a n d s s h o u l d have a r e a s o n a b l e volume f r a c t i o n and a h i g h d i s p e r s i o n , as Ivell a s a h i g h q u a l i t y . To do t h i s , we s e l e c t "a low t e m p e r a t u r e h e a t - t r e a t m e n t and a h i g h nunber o f f i l a m e n t s h s a t e c h n i c a l r e a l i - z a t i o n . A h i g h number o f f i l a m e n t s s u g g e s t s a f i n e d i a m e t e r o f t h e f i l a m e n t s f o r a giver? s t r a n d s a n d h a s a d u a l e f f e c t of widening t h e d i s p e r s i o n of NbjSn phase and f o r m a t i o n o f s u f f i c i e n t amount o f Nb3Sn phase d u r i n g low t e n p e r a t u r e h e a t - t r e a t m e n t due t o t h e i n c r e a s e d a r e a of s u r f a c e on which r e a c t i o n t a k e p l a c e . A h i g h nunber o f f i l a r l e n t s

( i . e . small d i a n e t e r of f i l a n e n t s ) i s a g r e a t h e l p t o improvement i n

c u r r e n t c a r r y i n g c a p a c i t y a s w e l l a s m e c h a n i c a l p r o p e r t i e s . I t i s w e l l knov~n - t h a t t h e low t e m p e r a t u r e heat-treat::!ent i s f a v o u r a b l e f o r f o r m a t i o n of f i n e g r a i n Ab3Sn and herlce a l s o f o r a h i g h e r v a l u e o f c r i t i c a l c u r r e n t d e n s i t y Jc. It must be p o i n t e d o u t , h o w e v e r , t h a t a h i g h number o f f i l a m e n t s ( i . e . s m a l l d i a m e t e r o f f i l a m e n t s ) i s a pre- r e q u i s i t e of t h e low t e m p e r a t u r e h e a t - t r e a t m e n t . The h e a t - t r e a t m e n t f o r s h o r t d u r a t i o n h a s been u s e d t o p r o v i d e a r e a s o n a b l e volume f r a c - t i o n o f BbgSn.

A s a p a r . t i c : ~ l a r cxai,lple v;e s e l e c t 330-700 Fb f i l a m e n t s f o r a s t r a n d and 6 5 0 - 7 3 0 ' ~ x 1 0 - 2 0 h r f o r h e a t - t r e a t m e n t regime. I n t a b l e ( 2 ) i t shows t h e t y p i c a l d a t a o f t h e components o f t h e s t r a n d s b e f o r e and a f t e r h e a t - t r e a t n e n t . The d i a m e t e r o f i J b c o r e i s l e s s t h a n 5 p m b e f o r e r e a c t i o n l i e a t - t r e a t n e n t , ItbjSn l a y e r s have a n a r e a f r a c t i o n o f 2076 and a t h i c ' m e s s o f l & m a n d t h e mi.nimum d i a m e t e r o f unreac.t;ec? Nb i s 1.7JJm. The ;?rain s i z e o f t h i s iJb3Sn p h r s e was d e t e r m i n e d by SEIJ t o be a b o u t 750-803 1. These d a t a shov: t h a t t h e s t r a n d s do n e e t t h e r e q u i r e m e n t s t h z t Nb3Sn p h a s e s h o u l d h a v e a r e a s o n a b l e volu..r~e f r a c - t i o n and wide d i s p e r s i o n a s w e l l as a h i g h q u a l i t y . T h e r e f o r e , i t i s s a f e t o s a y t h a t t l i e t e c h n i c a l r e a l i z a t i o n a n d p r o c e s s p a r a n e t e r s we have s e l e c t e d can b r i n g o u r d e s i g n p r i n c i p l e f o r t h e p r e - r e a c t e d c o n d u c t o r s i n t o o p e r a t i o r : a n d t h e p e r f o r x a n c e c h a r a c t e r i s t i c s o f t h e s h o r t s a m p l e s and t h e c o i l s s h o ~ v s th a t t h e a 5 o ~ r e d e s i g n c o n s i d e r a t i o n a r e e s s e n t i a l l y c o r r e c t .

B i t h o u g h , t h e o r e t i c a l l y spealcing, a more 1ov;er t e n p e r a t u r e c a n be u s e d f o r t h e h e z t - t r e a t m e n t , i t t a l r e s t o o l o n g n t i m e f o r t h e con- v e ~ i e l z t o p e r a t i o c . A s t i l l h i ~ h c r nilrnhcr o f f i l a r n e r l t s i s a l s o u c f a - v o a r a b l e b e c a u s e t h i s call c a u s e a t o o s m a l l s p a c e between t h e n e i g h - b o u r i n g f i l a m e n t s a n d h e n c e t h e i r c l o s e c o n t a c t b e c a u s e o f t h e i n - c r e a s e i n t h e v o l u n e o f Eb a f t e r c c n v e r s i o n t o Eb7Sn, t h u s r e s u l t i n <

i n ~ i l e d i a m e t e r o f t h e f i l a l a e r l t s t o be t o o l a r g e f o r a low a c l o s s . On tlie o t h e r !land, e x c e s s i v e nunlber of f i l m e n t o ( i. e . t o o s m a l l a d i x n e t e r o f f i l a m e n t s ) c a n l e a d t o an u - n r e a s o n a b l e a m l i n t o f NS3Yn, and t h e r e b y t h e e . > ~ : : r i i t l e . . l e n t o f t h e c o n d u c t o r s u n d e r p r e s e n t h e a t - t r e a t d e n t regirne. 'L'o o b t a i n t h e c o n d u c t o r s w i t h a r e a s o l i a 3 l e f r a c t i o n o f :ib3Jn t h e t i n e f o r t h e r e a c t i o n h e a t - t r e a t m e n t s h o u l d Se l e s s t h a n 1 0 h r a t 651°2 if a t o o h i g h nu!nhcr o f f i 1 a : n e n t s ( e . g . 1300 f i l a m e n t s , w i t h a d i a m e t e r of 2 p m ) h a v e b e e n u s e d f o r t h e s t r a n d s of which t h e c o n d u c t o r s c o n s i s t , t h u s r e s u l t i n g i n a p o o r supercon- d u c t i v e p e r f o r m a n c e b e c a u s e t h e Fb-Sn p h a s e fonned i s f a r from s t o i - c h i o m e t r y . / 2 /

The p r e l i m i n a r y t e s t s have shown t h a t b o t h b r a i d s and c a b l e s e r e small i n a c l o s s ( c o c p a r a b l e t o t h a t o f N b ~ i - C u ~ i i - C u ) a n d s e e n t o n c e t t t e r e q u i r e g e n t s i n h i g h s p e e d e x c i t a t i o n a n d t h e p u l s e f i e l d .

llhe b r a i z s p r e s e n t e d h e r e h a v e would i n t o d i p o l a r so3.cl ma,Vet ( $76 x 3 0 0 m ) f o r a a c c e l e r a t o r s n d t h e t e s t shows t h a t t h i s t y p e of c o n d u c t o r s c a n b e a r t h e s e v e r e b e n d i n g l o a d ( u p t o 9 :cia i n b e n d i n g r a d i u s ) a p p l i e d by t h e end o f t h e magnet. !?he f a b r i c a t i o n o f tile h i g h f i e l d n-a,met from t h e c a b l e s i s u n d e r way and would l e z d t o a 10T magnet.

R e f e r e n c e s

1. J c k e r t , D e t a l , C r y o g e n i c s 22 4 ( 1 9 8 2 ) 1 8 4

2 . L a r b a l e s t i e r , D.C. e t a l , P r o c . o f LiT-6 ( B r a t i s l a v a , 1978)1383

J O U R N A L DE PHYSIQUE

Table

(

1

)

Design Details of the Braids a n d Cables s i x

o f

1

^{, .,sty.:ds}

cross rcction

( m m x mm) n o - o f din. I twist p ~ t c h ' no.

I

s t r . ( m m ) , ( m m ) , N b

Table

(

2

)

?'he Components of Strands before a n d after R e a c t i o n

-- ---.-

-

.-

he fore reaction

!

a fter reaction

- - .. .

- - - -- I

h e a t -

I

^treatment

I S n % I d ~ b ( n ~ ; l l ; . . % ~ B . %

I S 1 ~ % A

^,

S ~ % ~ ~ ~ .

^((rm)

( ~ ) ~ ' ~ ^% : IF ~ ^..% ~ ¹ ~ ~ ^resime " [ ~ ~ ~ ~ ~ ~ \ ~ ~ ~ %

--

I

i

I

'

. .

- - L -L - -L-..

..-.I - -

301 112.67

1

4 I

'

25.6 , 74.4 17.86

1

^4.81

1

^3.0

1

^4.4

(

^0.7

1

^13.6

,

^16.7

¹

^69.7 1 6 5 0 ° ~ x 2 0 h r

I

^{, ,}

-

i03 '12.48 _{I :} 2.7

1

^25.6

1

^{74.4 i7.261 5.22}

;

1.7

[

2.9

1

^{0.6 10.7 20.5}

1

68.8 1 6 5 0 " c x 1 2 h r

S n x , A%Sn-Sn c o n t c n t a n d S n consumption i n bronze matrix respectively d,,-diameter of Nb core before a n d a f t e r reaction

d,b+,,,,,-diametcr of Nb core w i t h a Nb,Sn layer after reaction 6 , b3s,-thickncss of Nb,Sn layer

F,,%, F , , % , FSb3,,%-area fraction o f Nb, bronze a n d Nb,Sn respectively

Table

(

3

)

Performance Characteristics of Coils

Parameters

of

coils

I !

.

I '

I

^{i l0.d h}

^{I L W}

^I.

^{H 1 Jc(str.)* 1}

JC(cond.)*! J c ( s t r . ) x

H ' ^,

,,,,

^,

,,,,!

,cm,, n

I(:/:) ¹

^chf)

¹

^{( A )}

1 ^0')

( A I c m z )

/

^{(AIcm:) c*-T/cmz)}

_I

-

0- I 2.5

1

^7.7

^/

^6.0

1

⁸⁸⁰

1

¹⁴⁰

1

¹⁴⁰

;

^1.05

^j

⁵⁰⁰

)

7.0

1

1 . 1 2 ~ 1 0 5

1

^3.97x10'

^j

7 . 8 7 ~ 1 0 s

1

braid. 301 fil.

. -. -. - - - -- - -. - - -

R-:. 1

^{2 . 5 ; 9.1 , 9.3 1781}

1

²⁰⁴

1

324 ( 2 . 3 3 / 420

1

^8.51

/

^O.Bdxlos

1

^3.18x10L

i

^8.06x10'

¹

- - . . . -.

-

. - . . . . -. - - - - - - . - - .- - - -- . - B- 3 2.5 ; 8.7 9.5

1

¹⁹²⁹

1

^{220 330}

⁾

^{2.17 370}

1

^8.14

1

0 . 8 3 ~ 1 0 1

1

2.8 x 104

I

8 . 7 6 ~ 10s

I

braid, 703 f i l .

-. - -. - - -. .- - -. . -. -. .- -

C- 1 1 4.0 6.5 I 9.6

1

⁴²¹⁶

i

⁵⁰⁸

ⁱ

^{700 0.8 128}

^,

^6.5

1

1 . 3 9 ~ 10s

I

R.05x 104

/

9 . 0 4 ~ 1 0 ~

I

cablc, 703 fil.

-

- -

- - - .- - .- - .-

-

-. . -. . . .

-

-. . .- -

C - 2 ,

.

4.0 m 7 . 0 , 9.2 6500

/

738 11110 11.25 - --

1

¹⁰⁰ --

1

^7.38 -

^j

I . O ~ ~ I O J -

1

6.2gxiod

1

^7.97x1os

I

. . -cable, 301 . -. 111.

-

C - 3 3.0 7.5

1

12 ,12864

1

^{1234 , 2100}

1

^2.14

i

65

1

^8.02

1

^o.7ix1os

1

^4.ogx104

1

5.69x103

1

cable, 703 f i l .

*applying to J , of the c o i l s under self-field

**sparse widing and wax f i x t u r e f o r No,B- 1 , B-2, and B - 3 coils, but dense w i n d i n g

a n d n o f i x t u r e f o r No,C- 1 , C - 2 , and C - 3 coils,