NEW MULTIFILAMENTARY SUPERCONDUCTING WIRES WITH FILAMENT OF Nb3Sn IN SITU WIRES

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NEW MULTIFILAMENTARY SUPERCONDUCTING WIRES WITH FILAMENT OF Nb3Sn IN SITU

WIRES

F. Sumiyoshi, K. Funaki, Y. Akenaga, J. Chikaba, N. Mori, K. Yamafuji

To cite this version:

F. Sumiyoshi, K. Funaki, Y. Akenaga, J. Chikaba, N. Mori, et al.. NEW MULTIFILAMENTARY SU-

PERCONDUCTING WIRES WITH FILAMENT OF Nb3Sn IN SITU WIRES. Journal de Physique

Colloques, 1984, 45 (C1), pp.C1-383-C1-386. �10.1051/jphyscol:1984177�. �jpa-00223733�

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JOURNAL DE PHYSIQUE

Colloque C l , supplément au n° 1, Tome 45, janvier 1984 page Cl-383

NEW MULTIFILAMENTARY SUPERCONDUCTING WIRES WITH FILAMENT OF N b3S n I N

SITU WIRES

F . S u m i y o s h i , K. F u n a k i , Y. Akenaga, J . C h i k a b a * , N. Mori and K. Yamafuji

Department of Electronics, Kyushu University 36, Fukuoka 812, Japan

* Department of Electrical Engineering, Kinki University, lizuka 820, Japan

** Department of Metallurgical Engineering, Kyushu University 36, Fukuoka 812, Japan

Résumé - Nous proposons un nouveau type de conducteur supraconducteur multi- filamentaire utilisable pratiquement. Il s'agit d'un fil dans lequel les fila- ments sont formés in situ par un procédé de diffusion interne.

A b s t r a c t - As a superconducting in situ wire f o r a p r a c t i c a l use, we propose a new type of a m u l t i f i l a m e n t a r y w i r e , i . e . , a stuck w i r e w i t h f i n e cores which c o n s i s t o f in situ processed wires of an i n t e r n a l d i f f u s i o n type.

Although in situ processed Nb3Sn w i r e s have m e r i t s i n t h e i r simpler f a b r i c a t i o n p r o - cesses and smaller s t r e s s e f f e c t s on the c r i t i c a l c u r r e n t d e n s i t y , they have not been manufactured f o r a p r a c t i c a l use. This i s because they have demerits i n t h e i r lower c r i t i c a l c u r r e n t d e n s i t i e s , s m a l l e r c u r r e n t c a p a c i t i e s per a w i r e , and extremely l a r g e r h y s t e r e s i s losses s i m i l a r t o t h a t o f a s i n g l e - c o r e superconductor / 1 , 2 / .

The purpose of t h i s paper i s t o propose a new type o f p r a c t i c a l in situ Nb3Sn wires w i t h a l a r g e c u r r e n t c a p a c i t y and a low ac l o s s . For t h i s purpose, we a t f i r s t s t u d i e d e x p e r i m e n t a l l y electromagnetic p r o p e r t i e s of a s i n g l e in situ w i r e . Using the obtained r e s u l t s , we discuss the design p r i c i p l e of a new type w i r e . A t e s t w i r e was manufactured t o examine our design p r i n c i p l e .

I - ELECTROMAGNETIC PROPERTIES OF A SINGLE in situ WIRE

In t h i s s e c t i o n , we discuss the e l e c t r i c coupling among Nb3Sn f i l a m e n t s i n a s i n g l e in situ w i r e which plays the r o l e o f a f i n e core i n the present type o f stuck w i r e . We prepared in situ processed Nb3Sn wires of i n t e r n a l d i f f u s i o n t y p e . As i l l u s t r a t - ed schematically i n F i g . 1 , the region 2 i s occupied by Cu-22wt%Nb f a b r i c a t e d by the arc m e l t i n g method. The center of t h i s p a r t was d r i l l e d and a Cu hollow c y l i n d e r f i l l e d up w i t h 60vol%Sn-prepacked Cu powder / 3 / was i n s e r t e d i n t o t h i s d r i l l e d space.

Then they were mounted i n s i d e a Cu-10wt%Ni j a c k e t , which i s expected t o prevent the w i r e from breaking during the cold drawing process. I n i t i a l and f i n a l diameters o f the w i r e are 12.5mm and 0.3mm, r e s p e c t i v e l y , and the r e s u l t i n g r e d u c t i o n r a t i o i s about 1700. The sample wires were wound i n t o s i n g l e - l a y e r e d , solenoidal c o i l s w i t h the diameter of 35 mm and the heat treatment was c a r r i e d out a f t e r the w i n d i n g . Effective diameter at high fields: As a q u a n t i t a t i v e measure of the coupling among Nb3Sn f i l a m e n t s , the parameter def f c a l l e d the e f f e c t i v e diameter has often been used. According t o Shen's d e f i n i t i o n / 2 / , def f i s given by

< M >2 R = h ^^c^eff' ( 1 )

where <M>?R and <Jc>2P, a r e *n e transverse magnetization and the c r i t i c a l c u r r e n t den- s i t y averaged over thie region of O l r i R shown i n F i g . 1 r e s p e c t i v e l y , and v - 1 i s a Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984177

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C 1-384 JOURNAL DE PHYSIQUE

c o r r e c t i o n f a c t o r t a k i n g account o f the e f f e c t s o f the i n n e r bronze r e g i o n .

Measurements were c a r r i e d o u t f o r t h e cases o f t h e e x t e r n a l t r a p e z o i d a l f i e l d s w i t h a h e i g h t o f Em = 0.1 T o r 0.2 T and a minimum r i s e o r f a 1 1 time o f 1 sec superposed onto the various b i a s f i e l d s o f Bdc= 61.12 T. The observed curves o f minor magneti- z a t i o n had n o t sweep-rate dependences. With the a i d o f the data, the values o f deff were c a l c u l a t e d from Eq. (1) and are p l o t t e d a g a i n s t b i a s f i e l d i n Fig.2. We can f i n d the value o f d f f i s given by deff/2R1. 0.7 over t h e range o f 61.12 T. Thus, we can conclude t h a t tRe electromagnetic behaviors o f the i n s i t u w i r e are q u i t e s i m i - l a r t o those o f t h e s i n g l e - c o r e superconductor even a t h i g h f i e l d s .

E f f e c t i v e diameter i n the presence of transport c u r ~ e n t s : I n order t o i n v e s t i g a t e t h e e f f e c t o f t r a n s p o r t c u r r e n t s on d ^ff,we measured t h e l o s s o f an i n s i t u w i r e c a r r y i n g a dc t r a n s p o r t c u r r e n t i n e x t e r n a l transverse pul s e - f i e 1 ds

.

Measurements were c a r r i e d o u t f o r t h e sample c o i l s No.A3 and A3' by the s o - c a l l e d c o i l - s i m u l a -

t i o n method /4/ i n t h e b i a s transverse f i e l d o f 2T. I n Fig.3(a) and ( b ) , observed magnetization losses and dynamic r e s i s t a n c e losses /5/ are shown, r e s p e c t i v e l y . I t must be noted t h a t these data are independent o f the sweep r a t e w i t h i n t h e present experimental accuracy. We can use t h e o r e t i c a l expressions d e r i v e d by Ogasawara e t a l , / 5 / i f we assume t h a t t h e electromagnetic behavior o f i n s i t u w i r e s i s the same as t h a t o f a s i g l e - c o r e superconductor w i t h the diameter o f deff, and the t h e o r e t i - c a l r e s u l t s show good agreements w i t h observed data.

I 1

-

EXPECTED PROPERTIES OF A STUCK WIRE WITH MANY FINE i n s i t u Nb,Sn CORES I n t h i s section, we s h a l l show some examples o f design o f the present type o f in s i t u stuck w i r e t a k i n g account o f t h e purpose o f i t s a p p l i c a t i o n f o r h i g h - f i e l d pulse magnets. An example o f t h e design i n t h i s case i s shown i n Table 11, where the Nb content i n CuNb i s supposed t o be as h i g h as 35wt% i n order t o have a l a r g e c u r r e n t density.

The f i r s t p r i n c i p l e on t h e design o f the p r e s e n t s t u c k w i r e i s t o o p t i m i z e the amount o f the h y s t e r e s i s loss compared w i t h the c o u p l i n g - c u r r e n t l o s s among i n s i t u cores. I t must be n o t e d t h a t the present stuck w i r e i s a l s o t w i s t e d i n the same manner as t h e o r d i n a r y m u l t i f i l a m e n t a r y w i r e t o decrease t h e c o u p l i n g c u r r e n t l o s s . We assumed, t h e r e f o r e , t h a t ac losses i n t h e present w i r e can a l s o be estimated by the e x i s t i n g t h e o r i e s on t h e o r d i n a r y mu1 ti f i l a m e n t a r y wire, which wi 11 be confirmed e x p e r i m e n t a l l y i n t h e n e x t s e c t i o n . The values o f losses were estimated f o r t h e ex- t e r n a l f i e l d c o n d i t i o n s f o r windings o f a b i a h - f i e l d c o n d i t i o n as Bdc = 12 T,

Bm

= 0.5 T and tl = 0.1 sec which are t y p i c a l c o n d i t i o n 5 f o r windings o f a h i g h - f i e l d pulse magnet i n Kyushu U n i v e r s i t y / 6 / . We can f i n d t h a t the h y s t e r e s i s l o s s i s s l i g h t l y s m a l l e r than t h e c o u p l i n g l o s s , which seems t o be an optimized design under a given amount o f t o t a l l o s s .

The second p r i n c i p l e i n t h e present design i s r e l a t e d t o t h e electromagnetic proper- t i e s i n t h e presence o f t h e t r a n s p o r t c u r r e n t . I n t h i s case, i t has been p o i n t e d o u t by us /7/ t h a t t h e c u r r e n t u n i f o r m i n g time-constant T~~ d i f i n e d by

R ? &R B,

should be taken i n t o account t o discuss t h e c u r r e n t d i s t r i b u t i o n i n mu1 ti f i lamentary wires, where Rb i s a r a d i u s o f a core bundle and X i s t h e volume f r a c t i o n o f cores w i t h a r a d i u s o f R. Under t h e c o n d i t i o n o f T ~ ~ > > tl

,

t h e t r a n s p o r t c u r r e n t d i s t r i b - utes u n i f o r m l y . When T << t,

,

on t h e o t h e r hand, a l o c a l i z e d t r a n s p o r t c u r r e n t flows near the w i r e shpface. Since the l o c a l i z e d c u r r e n t d i s t r i b u t i o n has a s t r o h g p o s s i b i l i t y f o r t h e occurrence o f f l u x jumps and o f a l a r g e dynamic r e s i s t - ance l o s s , t h e value o f T~~ should be designed as small compared w i t h t h e r i s e o r the f a l l t i m e t, i n o r d e r t o use the w i r e i n the concerned pulse magnet. Compared w i t h o r d i n a r y NbsSn m u l t i f i l a m e n t a r y w i r e s i n which TIO i s q u i t e l o n g due t o the small f i l a m e n t diameter l i m i t e d t o a few microns o r so by a s h o r t d i f f u s i o n l e n g t h o f Sn i n Nb, we can say t h a t the p r e s e n t type o f i n s i t u stuck w i r e has f l e x i b i l i t y

i n i t s design f o r v a r i o u s a p p l i c a t i o n s .

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111

-

ELECTROMAGNETIC PROPERTIES OF A TEST WIRE

I n o r d e r t o c o n f i r m the design p r i n c i p l e i n the i n s i t u stuck w i r e mentioned i n the previous s e c t i o n , we manufactured a t e s t w i r e o f the p r e s e n t type. We, a t f i r s t , prepared 19 i n s i t u Nb,Sn w i r e s w i t h 1.5mn i n diameter i n the same manner as men- t i o n e d i n t h e previous section. Next, each i n s i t u w i r e was shaped i n t o the one w i t h a hexagonal cross section. These shaped i n s i t u w i r e s were stuck i n s i d e the Cu-30wt%Ni j a c k e t , together w i t h 12 dummy Cu-lOwt%Ni w i r e s as a spacer. The o b t a i n - ed composite i n t h i s way was drawn t o a w i r e o f 1.5mm i n diameter. F i n a l diameters o f the i n s i t u bundle and each i n s i t a core were 740 pm and 110pm, r e s p e c t i v e l y , and a r e d u c t i o n r a t i o was about 7000. A f t e r t w i s t i n g t h e w i r e ( L = 90 m )

,

the heat treatment was c a r r i e d o u t a t 600°C d u r i n g 80 hours (-Fig.4).

The coup1 i n g time-constant .rc can be determined from t h e frequency c h a r a c t e r i s t i c curve o f c o u p l i n g c u r r e n t losses i n the small ac f i e l d case /8/. I n Fig.5(b), the observed frequency dependence o f the ac l o s s p e r c y c l e per u n i t volume o f the i n s i t u core bundle, w ( f ) , i s shown, where the f i e l d s amplitude was 0.3 mT and

Bdc

7

2 T. Since the measured frequency r e g i o n o f f = 0 . 5 % 1 0 H z was n o t s u f f i c i e n t - l y w ~ d e t o determine the c o u p l i n g time-constant d i r e c t l y by the observed data, we estimated t h e experimental value o f the c o u p l i n g time-constant w i t h the a i d o f the e x i s t i n g t h e o r e t i c a l expressions. The peak frequency

fhl

= (2nr;)-' was determined by searching the b e s t f i t between the observed curve o f w c ( f ) and the t h e o r e t i c a l one, and the r e s u l t i s given by fkl = 166Hz. From the comparison o f ^{T ;} between t h i s experimental value (0.96 sec ) and the t h e o r e t i c a l l y designed value (0.92 sec ) by u s i n g the c o n d u c t i v i t y o f the CuNi, i.e., o m = 7.1 x 1 0 6 ~ - 1 m - 1 , i t i s concluded t h a t o u r design o f the c o u p l i n g time-constant i s q u i t e s a t i s f a c t o r y .

Measurements o f t h e transverse magnetization < O Z R was a l s o c a r r i e d o u t i n a b i a s f i e l d o f 2 T. We obtained <M> R = 15.3mT independently o f t h e sweep r a t e

(< 0.05 T/sec). I t i s t o be note% t h a t t l ( = 2 sec) f o r t h e magnetization measurement i s much l o n g e r than the observed c o u p l i n g time-constant o f ^{T ; .} Thus the e x t e r n a l p u l s e f i e l d w i t h the sweep r a t e o f 0.05T/sec penetrated f u l l y i n t o the stuck wire, and hence t h e observed data o f t h e magnetization i s expected t o be e x p l a i n e d by t h e c a l c u l a t e d value o f the magnetization from a l l i n s i t u cores.

For t h e present t e s t w i r e , t h e c r i t i c a l c u r r e n t d e n s i t y averaged over the core r e - gion i n t h e stuck w i r e was given as <Jc>2R = 2 . 2 x 10' A/m2 a t 2 T. This small value may be a t t r i b u t e d t o a f a i l u r e o f the h e a t treatment o r drawing by handiwork i n manufacturing the t e s t wire. S u b s t i t u t i n g t h i s value o f <Jc>2R and deff/2R= 1 i n t o E q . ( l ) , we obtained the t h e o r e t i c a l value o f the magnetization as 6.3mT. The d e v i a t i o n o f t h i s order between theory and experiment may be accepted by t a k i n g account t h e unevenness o f the shape o f each i n s i t u core.

I V

-

CONCLUSION

The stuck w i r e w i t h many i n s i b processed Nb3Sn cores o f an i n t e r n a l d i f f u s i o n type proposed i n t h i s paper as a p r a c t i c a l i n s i t u w i r e seems t o have remarkable m e r i t s i n i ) simplar f a b r i c a t i o n and i i ) f l e x i b l e design.

References

/1/ Braginski

,

A. I. and Wagner, G. R. IEEE Trans. llagn. FtAG-17 (1981 ) 243 /2/ Shen, S. S. and Verhoeven, J. D. IEEE Trans. Kaqn. ~ ~ ~ r [ 1 9 8 1 ) 2 4 8 /3/ Nagata, S . and Matsuda, K. IMONO - 53 (1981 ) 686 ( i n Japanese)

/4/ Ezaki, T.. I r i e , F., Kl i p p i n g , G., Liiders, K., Natsushi ta, T., Ruppert, U., Takeo, M. Cryogenics 19 (1979) 731

/ 5 / Ogasawara, T., Takahasm, Y., Kanbara, K., Kubota, Y

.,

Yasohama, K. and Yasukochi

,

K. Cryogenics 19 ( 1 979) 736

/6/ I r i e , F., Yamafuji, K., T a E o , M. and Sumiyoshi

,

F. IEEE Trans. Magn. MAG-19 11983) 672 , - - - - , - -

/7/ Sumiyoshi

,

F., Koga, K., H o r i

,

H., I r i e , F., Kawashima, T. and Yamafuji

,

K.

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Cl-386 JOURNAL DE PHYSIQUE

( t o be p u b l i s h e d i n Cryogenics)

I 8 1 Sumiyoshi, F., I r i e , F. and Yoshida, K. J. Appl. Phys. - 51 (1980) 3807

F i g . 4 Photograph o f t h e c r o s s s e c t i o n

o f t h e in situ s t u c k t e s t w i r e .

1

^{* * /}

TABLE I Parameter of in situ w i r e s

T A B L E

1 1 Anexample o f in situ s t u c k w i r e

Fig.5 Frequency dependence o f t h e ac l o s s i n t h e s t u c k w i r e , where

- W ( f ) ,

-

W(f)-W(0). B m = 0.83 [mT)

The s o l i d l i n e r e p r e s e n t s t h e

t h e o r e t i c a l v a l u e s o f Wc(f). l o

-22

^{l o 0} ^10' ^{l o 2}^f^{[ H Z ]}

Sample NO.

A1 '

A 3 L3' A4 ' . - - - - .

82 85'

F i g . 1 Cross s e c t i o n o f

t h e in situ w i r e . ^I, ^1.41 ³¹⁰ ⁶⁴⁰

a

CU-1 Owt%Ni ^{r ,} ^{~m secl} ^1.2 ^-10

@

CU-ZZwt%Nb ^W, IJ/m'cyclel 9 r 10' 6.4 x 10'

@

cu ^{W h} lJ/m'cyclel 4.2 * 10' 1.4 x 10'

@

CU+GOVO~ % ~ n ^{T I O} [msecl 2 2 1800

W 0.58 m it = 0.58

r 0.72

1 0 -: l o o

B m [ T I IFig.3 Bm dependences o f t h e m a g n e t i z a t i o n l o s s

WM and t h e dynamic r e s i s t a n c e l o s s Wg.

S o l i d l i n e s a r e t h e o r e t i c a l values.

D

, lml

2R fuml N

Lp Im)

Nb content I w t . a]

<J,>r,ZR lA/cm'l

<AJ > IA/cm1]

Dimension

- -

2R 21-0 wist pitch (urn) (urn) L (mm)

200 125

-

200 125 71

200 125

-

200 125

-

- - - . . - - -

-

- . - -

225 110 77

225 140

-

Heat treatment Temperature Tire

1.C) (hours)

558 100

627 168

600 100

- - - . - - -

-

- - - -

550 168

575 168

MF in sit" wires

2 132 128 50 35 1.8 x 10' 1.0 x 10'

Usual HF wires

2 4.3 49000

50

1 0 x 10' 2.0 x 10'