Jc(B,T) CHARACTERISATION OF SUPERCONDUCTING MULTIFILAMENTARY Nb3Sn MADE BY THE ECN METHOD

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Jc(B,T) CHARACTERISATION OF

SUPERCONDUCTING MULTIFILAMENTARY Nb3Sn MADE BY THE ECN METHOD

P. Hudson, H. Jones

To cite this version:

P. Hudson, H. Jones. Jc(B,T) CHARACTERISATION OF SUPERCONDUCTING MULTIFILA- MENTARY Nb3Sn MADE BY THE ECN METHOD. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-391-C1-394. �10.1051/jphyscol:1984179�. �jpa-00223735�

J (B/T) CHARACTERISATION OF SUPERCONDUCTING MULTIFILAMENTARY Nb3Sn MADE BY THE ECN METHOD

P.A. Hudson and H. J o n e s

University of Oxford, Clarendon Laboratory, Parks Road, Oxford 0X1 SPU, U.K.

Résumé - Contrairement au procédé "bronze" dont l'emploi dans la construction de bobines en Nb3Sn est très répandu, le procédé ECN qui suscite un intérêt croissant est basé sur la réaction de NbSn2 en poudre dans un tube de Nb pour la formation du Nb3Sn. Nous présentons des données JC(B,T) entre 4,2K etTc(0)et dans des champs allant jusqu'à 15.5T sur un échantillon de fil ECN/HOLEC mis à notre disposition par la Fondation Néerlandaise pour la Recherche en Energie.

A b s t r a c t - I n c o n t r a s t t o t h e r e l a t i v e l y w e l l - d e v e l o p e d b r o n z e p r o c e s s which has been f a i r l y e x t e n s i v e l y used i n t h e c o n s t r u c t i o n of s u p e r c o n d u c t i v e m a t e r i a l s , the ECN method i n which t h e r e i s a growing i n t e r e s t i s b a s e d upon t h e r e a c t i o n of NbSn2 powder i n a Nb tube f o r t h e p r o d u c t i o n of Nb3Sn. We p r e s e n t d a t a of J^C( B , T ) between 4.2K and T^c( 0 ) and i n f i e l d s up to 15.5T on a sample of ECN/HOLEC w i r e made

a v a i l a b l e t o us by the N e t h e r l a n d s Energy Research F o u n d a t i o n .

PRELIMINARY DISCUSSION

The c o n d u c t o r which i s the s u b j e c t of t h i s c h a r a c t e r i s a t i o n c o n s i s t s of 36 f i l a m e n t s of Nb3Sn i n a copper m a t r i x . The f i l a m e n t s a r e formed, a f t e r r e a c t i o n a t 675°C, under vacuum, from NbSn2 powder which i s c o n t a i n e d i n a Nb t u b e . I t s o v e r a l l d i a - meter i s 0 . 8 5 mm.

The JC( B , T ) c h a r a c t e r i s a t i o n , d e s c r i b e d h e r e , i s e s s e n t i a l l y a r e p e a t of t h a t which we produced for a b r o n z e - r o u t e m a t e r i a l and r e p o r t e d i n r e f . / l / . I n t h i s s t u d y , however, a l i m i t a t i o n of the e x p e r i m e n t a l probe became a p p a r e n t . This was t h e f i r s t time we had i n v e s t i g a t e d a c o n d u c t o r of d > 0.5 mm and we found t h a t , a l t h o u g h sample c u r r e n t , I s , of < 500 A i s a v a i l a b l e , f o r I s - 200 A e x c e s s i v e j o u l e h e a t i n g developed which the c l o s e d loop t e m p e r a t u r e c o n t r o l l e r could not combat. Our maxi- mum Jc range was t h e r e f o r e r e s t r i c t e d t o £ 350 A mm" . The maximum c u r r e n t l i m i - t a t i o n of t h i s , the f i r s t JC( B , T ) probe we have b u i l t , i s due t o t h e ohmic n a t u r e of t h e clamped c u r r e n t c o n t a c t s which a r e n o t c a p a b l e of w i t h s t a n d i n g a h i g h t i g h t e n i n g t o r q u e ; u n l i k e our range of JC( B , T ) p r o b e s which we have a l s o d e s c r i b e d i n r e f . / I / . We a r e , a t p r e s e n t , d e s i g n i n g two more JC( B , T ) p r o b e s i n which t h i s u n d e s i r a b l e f e a t u r e w i l l be e l i m i n a t e d . Apart from t h i s r e s t r i c t i o n on maximum J^c, t h e J^C( B , T ) d a t a we c o l l e c t e d followed t h e e x p e c t e d p a t t e r n and a r e p r e s e n t e d b e l o w .

We were concerned t o s e e t h a t the v a l u e s of JC( B , 4 . 2 K ) which we o b s e r v e d were con- s i d e r a b l y lower t h a n t h o s e o b s e r v e d , i n s i m i l a r m a t e r i a l , by Van Wees e t a l / 2 / . We s u s p e c t e d t h a t o u r sample may have s u s t a i n e d some p o s t - r e a c t i o n m e c h a n i c a l damage d u r i n g t r a n s f e r from t h e r e a c t i o n mandrel to t h e 31 mm diam. JC( B , T ) sample h o l d e r . As an i n d e p e n d e n t check we r e a c t e d a second sample t h i s time d i r e c t l y on a 19 mm sample h o l d e r , u s i n g a mounting t e c h n i q u e d e s c r i b e d e l s e w h e r e by Jones e t a l / 3 / , for i n v e s t i g a t i o n u s i n g one of o u r J ( B , 4 . 2 ) p r o b e s and o u r 16 T a l l - s u p e r c o n d u c t i n g magnet / 4 / . F i g (1) shows t h a t t h e r e s u l t s were n e a r l y i d e n t i c a l . In t h i s s e c o n d , f u l l y i n d e p e n d e n t t e s t , t h e r e was no p o s s i b i l i t y of sample damage and we c o n c l u d e t h e r e f o r e t h a t t h i s was not a problem. We t u r n e d o u r a t t e n t i o n t o t h e r e a c t i o n p r o c e d u r e . T h i s was 48-55 h r s , under a vacuum of 10~5 t o r r , a t a t e m p e r a t u r e of

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984179

Cl-392 JOURNAL DE PHYSIQUE

675OC + 5OC, a s recommended by t h e m a n u f a c t u r e r s . T h i s p r o c e d u r e was f o l l o w e d e x a c t l y f o r b o t h s a m p l e s . A check on t h e f u r n a c e t e m p e r a t u r e and p r o f i l e r c v e a l c d a n a x i a l s h i f t o f ?. 70 nun i n t h e f l a t temp- e r a t u r e r e g i o n . C o n s e q u e n t l y we e s t i m a t e t h a t t h e mean s a m p l e t e m p e r a t u r e was ^?. 15 t o 2O0C t o o low.

M - A p r e l i m i n a r y m i c r o g r a p h i c a l chcck i n d i c a t e d ,i d e g r e e

o f u n d e r - r e a c t i o n and t h i s c o u l d e x ~ l a i n t h e u n c h a r a c - t c r i s t i c a l l y low J s o b t a i n e d .

k:XI'ERTMENTAI. PROCEDURE AND ZERO rIELD XEASUEMENTS -

I n r e f / I / t h e p r o c e d u r e f o l l o w e d and t h e a p p a r a t u s u s e d i s d e s c r i b e d f u l l y . The e m e r i m e n t a l e q u i p m e n t

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t h e Rh-Fe r e f e r e n c e t h e r m o m c t e r . A f t e r t h e s a m p l e F i g . I . J c ( R , 4 . 2 K ) was f i t t e d , a s e r i e s o f z e r o f i e l d m e a s u r e m e n t s w e r e

made. F i r s t l y t h e t e m p e r a t u r e g r a d i e n t , a s a f u n c t i o n o f s a m p l e t e m p e r a t u r e , A T ( T ) was m e a s u r e d u s i n g t h e C O D and b o t t o m c a r b o n - g l a s s r e s i s t a n c e t h e r m o m e t e r s . AT(T) was found t o be 5 ⁺ 0 . 4 K . We t h e r e f o r e e s t i m a t e t h e s a m p l e t e m p e r a t u r e s q u o t e d a r e r e l i a b l e t o w i t h i n -i 0 . 2 K . N e x t , r e s i s t i v e m e a s u r e m e n t s were made. The f i r s t , u s i n g a s a m p l e c u r r e n t o f 5 A , y i e l d e d a Tc o f Tc

16.695 K. The s e c o n d , s a m p l e c u r r e n t = I A , g a v e Tc = 1 6 . 8 K. The l a t t e r measure- ment i s shown i n f i g . 3. At t h i s t e m p e r a t u r e l e v e l CT i s s u c h t h a t we e s t i m a t e t h e p o s s i b l e e r r o r a s + 0 . 2 K , - 0 K . N o n e t h e l e s s Tc i s c o n s i d e r a b l y l o w e r t h a n t h e

f i g u r e o f 18.5 K u s u a l l y a s s o c i a t e d w i t h s t r a i n - f r e e s t o i c h i o m e t r i c h%3Sn. % i s i s i n k e e p i n g w i t h o u r p r e v i o u s o b s e r v a t i o n s / I / .

The magnet u s e d f o r t h e Jc(I1,T) t e s t s was t h e Oxford h y b r i d magnet / 5 / i t s maximum f i e l d , a t p r e s e n t , i s 15.5T, a l t h o u g h p l a n s a r e i n h a n d t o u p - r a t e t h i s t o 20 T.

/ h / The f i e l d i s c a l i b r a t e d u s i n g a s e a r c h c o i l a n d a n e l e c t r o n i c i n t e g r a t o r (HP2401C) a g a i n s t a n nmr s t a n d a r d and t h e v a l u e s o f B q u o t e d s h o u l d b e w i t h i n +

0 . 0 3 T. S a m l e c u r r e n t i s m e a s u r e d u s i n g a c o m r c i a l s h u n t o f s t a t e d a c c u r a c y

+ 2 8 .

I n a g i v e n e x p e r i m e n t a l p e r i o d we w e r e a b l e t o make m e a s u r e m e n t s a t f o u r o r f i v e t e m p e r a t u r e s a t 0 . 5 K i n t e r v a l s . At t h e o u t s e t o f e a c h p e r i o d r h e f i e l d i n d e p e n d e n t t e m p e r a t u r e c o n t r o l t h e r m o m c t e r ( L a k e s h o r e C a p a c i t a n c e CS400) was c a l i b r a t e d , i n z e r o f i e l d , a ~ a i n s t t h e RhFe t h e r m o m e t e r . T e m p e r a t u r e c - o n t r o l was m a i n t a i n e d u s i n g t h e CS400 t h e r m o m e t e r , i n c l o s e d l o o p w i t h t h e h e a t e r w i n d i n g , v i a a L a k e s h o r e B r i d g e . The n u l l b a l a n c e i n d i c a t o r o f t h e bridge was c a l i b r a t e d s o t h a t a n o u t o f b a l a n c e s i g n a l o f 0 . 2 5 K c o u l d b e d e t e r m i n e d . T h i s was u s e d t o d e f i n e t h e p o i n t where we l o s t c o n t r o l o f t h e a d d i t i o n a l J o u l e

t e r m a t t h e t o p o f t h e .Jc r a n g e .

A t y p i c a l t r a n s i t i o n i s shown i n f i n . ( 4 ) t h e

t r a n s i t i o n i s qrli t e s h a r p , and t h i s a g r e e s w i t h ' z:,:::: ",,,.s.,h."",b.

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1 6 16'5 1 7 I T 5 o f t h e J c ( T ) c u r v e s ( f i g . 6 ) and n l o t Tc(B) v s .

TEMPERATURE/K R i n f i g . 7. \rTe can t h e n w r i t e :

F i g . 3 . R e s i s t i v e T, measurement

F i g . 4. T y p i c a l t r a n s i t i o n , B = l l.OT, T = 4 . 2 K

The d a t a c o l l e c t e d a r e shown i n f i z s ( 5 ) t o ( 7 ) . The c r i t i c a l c u r r e n t d e n s i t y J c i s de- f i n e d a s T c / a w h e r e a i s t h e c r o s s s e c t i o n a l a r e a o f t h e whole c o n d u c t o r .

W .

;lo 0 2

where m i s t h e s l o p e o f t h e r e s u l t a n t s t r a i g h t l i n e i n f i g . 7. I n t h i s c a s e t h e r e i s a some- what l a r g e r s c a t t e r t h a n i n t h e c o r r e s p o n d i n g

f i g u r e o f r e f . / I / b u t a comDuter g e n e r a t e d , s t r a i g h t l i n e f i t g i v e s m = -0.60 KT-', and m-' = -1.67 TK-'. These v a l u e s a r e r e m a r k a b l y s i m i l a r t o t h o s e we d e t e r m i n e d p r e v i o u s l y f o r t h e b r o n z e r o u t e m a t e r i a l (-0.61 and - 1 .h4 r e s - p e c t i v e l y ) . T,,(O), t h e i n t e r c e ~ t o f t h e s t r a i ~ h t l i n e a t z e r o f i e l d , a t 15. I K i s much l o w e r t h a n t h e r e s i s t i v e Tc measurement r e p o r t - e d a b o v e . T h i s i s t o be e m e c t e d a s o n l y t h e l i n e a r p a r t o f t h e .lc(B) c u r v e s a r e e x t r a ~ o l a - t e d t o z e r o .l .

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- 1 I , B w I ~ = ~ A .

S u b s t i t u t i n g t h e v a l u e s o f T c ( 0 ) and m i n t o e q u a t i o n ( I ) we o b t a i n :

which i s i n c l o s e a g r e e m e n t t o p r e v i o u s l y ~ u b l i s h e d work / 1 / / 7 / . CONCLUSTON

We c o n c l u d e t h a t t h i s s t u d y i n d i c a t e s t h a t t h e n o r m a l i s e d , t e m p e r a t u r e d e p e n d e n t b e h a v i o u r o f t h i s m a t e r i a l , a t t e m p e r a t u r e s h i g h e r t h a n 4 . 2 K , i s v e r y s i m i l a r Lo t h o s e p r o d u c e d by o t h e r r o u t e s . A l t h o u g h , b e c a u s e o f t h e r e s t r i c t e d J, r a n g e , r e - f e r r e d t o i n t h e p r e l i m i n a r y d i s c u s s i o n , we h a v e n o t i n v e s t i g a t e d Jc(B,T < 4 . 2 K ) , y e t , t h e i n d i c a t i o n s a r e t h a t t h e u s u a l s i g n i f i c a n t e n h a n c e m e n t s i n J c found i n o t h e r m a t e r i a l s a t T < 4 . 2 K c a n h e e x p e c t e d o f t h i s c o n d u c t o r .

I t must h e e m p h a s i s e d t h a t t h e low v a l u e s o f J c r e p o r t e d a r e n o t t y n i c a l o f t h i s c o n d u c t o r w h i c h h a s b e e n f o u n d t o e x h i b i t Jcs o f up t o t h r e e t i m e s t h o s e c h a r a c t t r - i s t i c o f b r o n z e r o u t e m a t e r i a l s / 2 / .

ACKNOWLEDGEMENTS

We w o u l d l i k e t o r e c o r d o u r e s p e c i a l t h a n k s t o M r . E.P. Gibbons f o r h i s h i g h l y c o m p e t e n t a s s i s t a n c e i n c a r r y i n g o u t t h e s e m e a s u r e m e n t s . Thanks a r e a l s o due t o o u r c o l l e a g u e s i n t h e D e p a r t m e n t s o f E n ~ i n e c r i n g S c i e n c e a n d M e t a l l u r g y , i n O x f o r d , f o r ~ r o v i d i n g s p e c i a l i s t s e r v i c e s . The c o n d u c t o r was g e n e r o u s l y s u p p l i e d by H o l e c Wire and f i n a n c i a l s u p p o r t came from t h e S c i e n c e and E n g i n e e r i n g R e s e a r c h C o u n c i l .

(The d e a t h o f P.A. Iiudson, d u r i n g t h e p r e p a r a t i o n o f t h i s p a p e r , i s r e n o r t e d w i t h much r e g r e t . )

Cl-394 JOURNAL DE PHYSIQUE

O

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O/T

F i g . 7. Tc(B) vs B.

F i g . 5 . J c v s B f o r 4.2 K < T < 1 . HUDSON P.A., Y I N F.C. and JONES H., 17.0 K . Two s e t s o f 4 . 2 K d a t a p o i n t s I E E E T r a n s Mag., MAG19, 3 , (1983) a r e shown. "Gas" r e f e r s t o m e a s u r e m e n t s ^{D .} 903.

w i t h p r o b e c o v e r i n lace. " L i q u i d " means

t h a t t h e s a m p l e was i n d i r e c t c o n t a c t 2. VAN WEES A.C.A., HOOGENDEN P . and w i t h L i q ; 4 ~ e . The 9 . 5 K and 9 . 0 K WRINGA H . , IEEE T r a n s . Mag., MAG19, c u r v e s show ( d a s h e d ) t h e e f f e c t o f ohmic 3 , (1983) p . 556.

s a m p l e h e a t i n g c a u s i n g a t e m p e r a t u r e

r i s e o f 0 . 2 5 K and 0 . 5 K r e s p e c t i v e l y . 3 . JONES H . , HUDSON P,.A., HASCICEK Y.S., NOURBAKHSH S. and GORINGE M. J . A c c e p t e d f o r ~ u b l i c a t i o n i n Cryo- g e n i c s ( 1 9 8 3 ) .

HUDSOK P.A. a n d JONES H . , C r y o g e n i c s 16, 10 (1976) D. 593.

-

HIIDSON P . A . a n d JONES H . , C r y o g e n i c s 2 0 , I0 (1980) D. 593.

-

HUDSON P.A., JONES H . and WHITWORTH H.M., P a p e r 2p2-02, T h i s c o n f e r e n c e . SCHAUER W . and ZIMMERMAN F . , &.

Cryo. Eng. 6 (1980) p . 432.

T c... mir..c/.

F i g . 6. J c v s T f o r OT < B < 15.5T