TEMPERATURE DEPENDENT AC LOSS MEASUREMENTS ON NbTi AND Nb3Sn SUPERCONDUCTORS BETWEEN 4.2 K AND 1.8 K

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TEMPERATURE DEPENDENT AC LOSS MEASUREMENTS ON NbTi AND Nb3Sn

SUPERCONDUCTORS BETWEEN 4.2 K AND 1.8 K

E. Seibt, D. Tabarsi

To cite this version:

E. Seibt, D. Tabarsi. TEMPERATURE DEPENDENT AC LOSS MEASUREMENTS ON NbTi AND

Nb3Sn SUPERCONDUCTORS BETWEEN 4.2 K AND 1.8 K. Journal de Physique Colloques, 1984,

45 (C1), pp.C1-475-C1-478. �10.1051/jphyscol:1984197�. �jpa-00223753�

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JOURNAL DE PHYSIQUE

Colloque C1, supplement au n o 1, Tome 45, janvier 1984 page Cl-475

TEMPERATURE DEPENDENT AC LOSS MEASUREMENTS ON N b T i AND N b 3 S n SUPERCONDUCTORS BETWEEN 4 a 2 K AND 1 n 8 K

E.W. Seibt and D. ~abarsi'

Kemzforschungszentrwn Karlsruhe, I n s t i t u t fur Technische Physik, Postfach 3640, 0-7500 Karlsruhe I , F.R. G .

Riesumi!

-

Des mesures de pertes e f f e c t u d e s s u r des supraconducteurs mul-

€iTl%entaires en NbTi e t en Nbj-Sn reagi, a' bronze d i f f u s e , sont d e c r i t e s en f o n c t ~ o n de champs magnetiques d impulsions en t r i a n g l e appliques dans l e domaine de basses frequences ( f < 5 Hz) e t aux temperatures se s i t u a n t e n t r e 4,2 K e t 1,5 K. A f i n d l @ t u d i e r l e comportement des p e r t e s

a

1,8 K ( r @ - f r i g e r a t i o n a' he1 ium 11) compare au comportement dans l e cas de r e f r i g e r a t i o n au b a i n d ' h e l i u m d 4,2 K, on a c h o i s i deux representants typiques d ' e c h a n t i l l o n s composes, c.

Z

d. un conducteur de t y p e EURATOM-LCT e t un cBble p l a t en NbqSn.

Les r 6 s u l t a t s de pertes'obtenus d 1,8 K e t normalises a' 4,2 K i n d i q u e n t qu une l e n t e augmentation a l i e u avec 1 'augmentation du taux de changement du champ e t que l e comportement e s t d i f f e r e n t pour l e s amplitudes de champ p l u s p e t i t e s que l e champ de p e n e t r a t i o n Hp

-

^{1/2 d}

^.

j c . ( d = diametre du f i l a m e n t ) . Les termes responsables des pertes par h y s t 6 r e s i s e t par l e s courants de Foucault sont d i s c u t e s .

Abstract

-

AC l o s s measurements on NbTi and bronze-diffused r e a c t e d Nb3Sn mul- t i f i l a m e n t a r y superconductors a r e described as a f u n c t i o n o f a p p l i e d t r i a n g u l a r

pulse magnet f i e l d s w i t h i n t h e low-frequency r e g i o n ( f < 5 Hz) f o r temperatures i n t h e range between 4.2 K and 1.5 K. To study t h e l o s s behavior w i t h 1.8 K helium 11 c o o l i n g compared t o helium-bath c o o l i n g a t 4.2 K, two t y p i c a l r e p r e - s e n t a t i v e s o f superconducting composite samples, t h e EURATOM-LCT conductor and a Nbg-Sn f l a t cable, were chosen. The r e s u l t s obtained f o r t h e losses a t 1.8 K and normalized t o 4.2 K show a slow increase w i t h increased f i e l d change r a t e and a d i f f e r e n t behavior f o r f i e l d amplitudes s m a l l e r than t h e p e n e t r a t i o n f i e l d Hp z 1/2 d .jc ( d = f i l a m e n t diameter). Responsible h y s t e r e s i s and eddy c u r r e n t l o s s terms a r e discussed.

I

-

INTRODUCTION

AC losses i n m u l t i f i l a m e n t a r y NbTi and NbjSn superconductors have been e x t e n s i v e l y r e p o r t e d t h e o r e t i c a l l y / I / as w e l l as e x p e r i m e n t a l l y /2/. However, o n l y a few i n - v e s t i g a t i o n s r e l e v a n t t o p r a c t i c a l a p p l i c a t i o n s have been made on the temperature dependence o f t h e ac losses i n a p p l i e d pulsed magnetic f i e l d s .

F. I r i e e t a l . /3/ found anomalous temperature dependent increments o f ac losses caused by f= jumps which can be explained q u a l i t a t i v e l y by t h e temperature dependence o f s p e c i f i c heat t r a n s f e r and t h e p i n n i n g f o r c e c o n d i t i o n s o f the supercon- d u c t i n g samples.

I n t h e present paper, some experimental r e s u l t s are given f o r the a l t e r n a t i n g t o t a l f i e l d losses as a f u n c t i o n o f the temperature i n t h e range o f 4.2 K t o 1.5 K. The purpose o f these measurements was t o i n v e s t i g a t e t h e l o s s c h a r a c t e r i s t i c s o f a t y p i - c a l NbTi and a Nb3Sn composite conductor system, r e s p e c t i v e l y , under two c o o l i n g con- d i t i o n s : ( 1 ) he1 ium-bath cool i n g and ( 2 ) cool i n g w i t h s u p e r f l u i d he1 ium. O f p r i n c i p a l i n t e r e s t , t h e i n v e s t i g a t i o n s were extended t o i n c l u d e the temperature i n f l u e n c e on the h y s t e r e s i s and t h e eddy-current l o s s p r o p o r t i o n s which can be separated by using conventional magnetization techniques.

I 1

-

EXPERIMENTAL PROCEDURES

Samples. To perform t h e ac l o s s measurements w i t h i n t h e temperature range between 4.2 K and 1.5 K f o u r d i f f e r e n t NbTi and Nb3Sn composite superconductors were used:

'D. Tabarsi is with the university o f Karlsruhe, Institut fGr Experimentelle Kernphysik

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984197

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C1-476 JOURNAL DE PHYSIQUE

( 1 ) A s h o r t sample o f t h e EURATOM-LCT-conductor /4/ c o n s i s t i n g o f 23 NbTi/Cu r e c t a n - g u l a r strands. ( 2 ) A f l a t cable conductor c o n s i s t i n g o f 12 Nb Sn strands o f 0.3 mm diameter each b u t w i t h o u t copper s t a b i l i z i n g elements. ( 3 ) A d b ~ i w i r e conductor w i t h pure copper m a t r i x . ( 4 ) A Nb3Sn w i r e conductor w i t h a pure copper core p r o t e c t e d by a Ta b a r r i e r .

I n Table I t h e measured samples Nos. 1

+

4 a r e described i n some d e t a i l .

Table I

-

Measured samples.

Measurements. The temperature dependent ac l o s s measurements w i t h o u t t r a n s p o r t c u r - r e n t l o a d a r e concentrated on two p o i n t s : ( 1 ) To measure t h e temperature i n f l u e n c e on t h e t o t a l losses as a f u n c t i o n o f t h e pulsed f i e l d amplitude i n comparison t o t h e p e n e t r a t i o n f i e l d B

,

and ( 2 ) t o determine the temperature dependence o f t h e hystere- s i s and eddy curren! l o s s o r o o o r t i o n s i n t h e ranae o f 4.2 K t o 1.5 K f o r a oeroen-

. .

d i c u l a r ac f i e l d amplitude'B ' = 2.5 T.

The t o t a l l o s s measurements h e r e performed on t h e EURATOM-LCT-conductor (No. 1) and a N b g ~ n f l a t cable (No. 2) a t 4.2.K and 1.8 K over a range o f magnetic f i e l d s from 0.1 T up t o 2.5 T using a thermal l o s s measuring technique. The momentary energy losses were determined by measuring t h e conductor surface temperatures o f t h e samples being i n a s t a t e o f thermal e q u i l i b r i u m w i t h t h e r e s i d u a l helium gas atmosphere. The temperature r e g i s t r a t i o n was made by carbon r e s i s t o r s . The l o s s data were c a l i b r a t e d by a h e a t i n g system (CuNi-wires) wound around t h e sample. The lower temperature range (4.2 K t o 1.5 K) was reached by pumping and h e a t i n g the helium-cryostat.

To determine the h y s t e r e s i s and eddy c u r r e n t l o s s e s o f t h e NbTi (No. 3) and Nb3Sn (No. 4) m u l t i f i l a m e n t a r y w i r e samples magnetization measurements were performed by pick-up c o i l s wound around the samples. The t r i a n g u l a r f i e l d sweep r a t e ranged from

el

= 0.05 t o 0.9 T/s. The pure h y s t e r e s i s losses were reached by stopping successi- v e l y t h e maanetization apparatus (8,- + 0).

I 1 1

-

RESULTS AND DISCUSSION

P a r t i a l and f u l l p e n e t r a t i o n losses a t 1.8 K and 4.2 K. The t o t a l l o s s measurements performed by t h e thermal l o s s method a t 1.8 K and 4.2 t? were l i m i t e d by t h e a v a i l - a b l e oeroendicular ac f i e l d amolitudes B, ( t r i a n a u l a r oulse mode) t o t h e o a r t i a l p e n e t r a t i o n case, Bf < Bg, and' t o t h e f u n 'penet;ation r e g i o n where BI > B

.

^{The B}

values f o r t h e pene r a t i n f i e l d were obtained from t h e l o s s measurements

gt

^{4.2 K'}

where t h e l o s s curves began t o d e v i a t e from a ~ ~ - d e ~ e n d e n c e . For t h e EURATOM-LCT- conductor (No. 1) i t was found B (4.2 K) = 0.20 T ( c a l c u l a t e d : 0.15 T ) , f o r the Nb Sn f l a t c a b l e (No. 2) 0.35 T r c a l c u l a t e d : 0.40 T). A comparison o f t h e measured a d c a l c u l a t e d Bp ,~alues i n d i c a t e s t h a t t h e measured Bp values are i n a f a i r agreement w i t h those expected i n b u l k superconductors given by t h e known formula f o r B (T) = 4nx10-7d.~ (T) i n MKS u n i t s ( d = f i l a m e n t diameter).

T R ~

temperature inf(iuence o f t h e t o t a l losses W t o t a l (sum o f h y s t e r e s i s losses Wh and eddy c u r r e n t l o s s p r o p o r t i o n s W e l l i n t h e low-frequency r e g i o n dependent of t x e ac f i e l d amp1 i t u d e s i n t h e range from 0.1 T t o 0.5 T (measured up t o 2.5 T) i s shown f o r a EURATOM-LCT-sample and a N b j Sn f l a t c a b l e i n Figs. 1 and 2, r e s p e c t i v e l y . I t can be seen t h a t t h e l o s s curves a t 1.8 K compared t o those a t 4.2 K a r e g e n e r a l l y c h a r a c t e r i z e d by a broad minimum which i s due t o t h e temperature dependence i n t h e frequency range o f 0.5 t o 2 Hz. For s m a l l e r frequencies below 0.5 Hz a s t r o n g i n - crease o f t h e losses a t 1.8

K

( f a c t o r 1.5 t 2.5 l a r g e r t h a n w i t h 4.2 K He c o o l i n g ) i s observed f o r both sample types (Nos. 1 and 2), whereas o n l y a s l i g h t increase of t h e 1.8 K losses i s i n d i c a t e d w i t h t h e increase o f frequency. However, i f t h e f i e l d amplitudes a r e smaller than the c h a r a c t e r i s t i c f i e l d Bp i n which t h e f l u x f r o n t

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F i g . 1

-

N o r m a l i z e d l o s s e s f o r 1.8 K F i g . 2

-

Normalized l o s s e s f o r 1.8 K and 4.2 K H e - c o o l i n g o f EURATOM-LCT- and 4.2 K H e - c o o l i n g o f a Nb3Sn f l a t

conductor (No. 1). c a b l e (No. 2).

reaches t h e m i d d l e p l a n e o f t h e sample, t h e p a r t i a l p e n e t r a t i o n l o s s e s w i t h super- f l u i d h e l i u m c o o l i n g (1.8 K) a r e reduced by up t o 50% compared t o t h o s e measured w i t h h e l i u m b a t h c o o l i n g (4.2 K). The B (TI-dependence o f t h e h y s t e r e s i s l o s s p r o - p o r t i o n seems t o be r e s p o n s i b l e f o r t h i e l o s s b e h a v i o r a c c o r d i n g t o t h e f o l l o w i n g p r o p o r t i o n a l i t y f o r f i e l d a m p l i t u d e s B I - < Bp:

T h i s agrees q u a l i t a t i v e l y w i t h temperature dependent p e n e t r a t i o n f i e l d measurements made on samples 2 and 4 where t h e 13 - v a l u e s s h i f t t o h i g h e r values w i t h d e c r e a s i n g temperature; e.g. f o r sample 2: Bp 11.8 K) = 0.50 T.

Temperature-dependent h y s t e r e s i s and eddy c u r r e n t l o s s e s . Loss d a t a f o r t h e tempera- t u r e range f r o m 4.2 K t o 1.5 K were o b t a i n e d by u s i n g t h e m a g n e t i z a t i o n t e c h n i q u e f o r NbTi/Cu (No. 3 ) and Nb3Sn/Ta/Cu (No. 4) w i r e c o n d u c t o r s as a f u n c t i o n o f d i f - f e r e n t f i e l d sweep r a t e s

O1

i n t h e f u l l p e n e t r a t i o n f i e l d o f BL = 2.5 T. T y p i c a l examples o f such t o t a l l o s s c u r v e s n o r m a l i z e d t o 4.2 K a r e shown i n F i g s . 3 t 5. The

7- - -.

- --- ^--

@

1

L914 ^I*^a-

9 k.09 tr.

= a,

-

^{I n}

i:!;;,. .

^{0 ,} ^.

\\

^*^-D . . l \ l ^am

'I\

,O,.- - - - - -

.-

^-^--

F i g . 3

-

Norn;alized t e m p e r a t u r e dependent F i g . 4

-

Normalized t e m p e r a t u r e dependent l o s s e s o f a NbTi/Cu sample (No. 3 ) . l o s s e s o f a NbgSn/Ta/Cu sample (No. 4 ) . r e s u l t s i n d i c a t e a d i f f e r e n t i n c r e a s e w i t h d e c r e a s i n g temperature and

kL.

F i g u r e 5 g i v e s a l s o a comparison between m a g n e t i z a t i o n d a t a and l o s s d a t a o b t a i n e d f r o m t h e thermal l o s s measurements. B o t h values a r e i n good agreement w i t h i n t h e e r r o r range.

The t h e w e t i c a l c o n t r i b u t i o n o f t h e h y s t e r e s i s l o s s e s t o t h e t o t a l l o s s i s n o t l a r g e below ElI.= Bp, b u t r a p i d l y b e g i n s t o dominate above t h i s value. F u l l p e n e t r a t i o n h y s t e r e s i s l o s s d a t a shown i n F i g . 6 i n d i c a t e a l i n e a r i n c r e a s e w i t h d e c r e a s i n g tem- p e r a t u r e as expected by t h e o r y / 5 / .

Eddy c u r r e n t l o s s e s We] caused by t r a n s v e r s e c o u p l i n g c u r r e n t s i n t w i s t e d m u l t i f i l a - mentary composites a r e a f f e c t e d by t h e t e m p e r a t u r e T o n l y i n so f a r as t h e t r a n s v e r s e e l e c t r i c c o n d u c t i v i t y o f t h e composites oL(T) i s a f f e c t e d . I n t h e 1 ow-frequency r e - g i o n i t i s expressed b y

Wel(T)/V

-.

pr 2

.

^{f 2}

-

^:⁶

.

^l2

.

^ol(T),

P ( 2 )

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JOURNAL DE PHYSIQUE

Fig. 5

-

Normalized losses f o r 1.8 K Fig. 6

-

Temperature dependent and 4.2 K He-cool i n g o f NbTi/Cu (No.3) h y s t e r e s i s losses o f NbTi/Cu (No.3)

and Nb3Sn/Ta/Cu (No.4).

-

and Nb3Sn/Ta/Cu (No.4).

where V i s t h e sample volume, p, t h e r e l a t i v e p e r m e a b i l i t y , f t h e frequency, and lp t h e t w i s t p i t c h . I n F i g s . 7 and 8 a r e summarized t h e temperature dependent eddy c u r r e n t l o s s r e s u l t s obtained f o r NbTi/Cu (No. 3 ) and Nb3Sn/Ta/Cu (No. 4 ) samples.

There seem t o be o n l y s l i g h t changes i n ul w i t h decreasing temperature and

8

f o r a pure Cu m a t r i x (Fig. 7); however, f o r a complex m a t r i x system as used i n sample 4, t h e eddy c u r r e n t losses show a more complicated temperature dependence i n the low- frequency r e g i o n ( F i g . 8 ) . T h i s e f f e c t may bedue t o the changes o f ol caused by the

---

^-,- ---,----

--

0 8

36 ---L---&--

0 2 G L O ~ ~ rrlcl 60 r n

Fig. 7

-

Normalized temperature Fig. 8

-

Normalized temperature dependent eddy c u r r e n t losses o f dependent eddy c u r r e n t losses o f

NbTi/Cu (No.3). Nb3Sn/Ta/Cu (No.4).

temperature dependent magnetoresistance o f t h e complex m a t r i x (CuSn/Ta/Cu), however, more work i s r e q u i r e d t o b e t t e r analyze t h e temperature dependent losses.

Concludin remarks. ( 1 ) F u l l p e n e t r a t i o n ac losses a t 1.8 K i n t h e low-frequency d a n those a t 4.2 K, whereas p a r t i a l p e n e t r a t i o n losses a r e s m l l e r i n a r e l a t i v e l y wide frequency range w i t h s u p e r f l u i d he1 ium cool i n g

.

^{( 2 )}H y s t e r e s i s and eddy c u r r e n t losses show a d i f f e r e n t behavior i n t h e i r temperature dependencies.

ACKNOWLEDGMENT

The authors wish t o thank M r . J. P y t l i k f o r t e c h n i c a l assistance.

References

1) Campbell, A.M., Cryogenics 22 (1982) 3.

2) Turck, B., Lefevre, F., P o l x , M., Krempasky, L., Cryogenics 22 (1982) 441 ; H l s s n i k , I., S e i b t , E.W., t o be p u b l i s h e d i n J . Appl

.

Phys. ( S p t . 1983).

3) I r i e , F., K l i p p i n g , G., Luders, K., Matsushita, T., Ruppert, K., Takeo, M., IEEE Transact. Magn. MAG-13 (1977) 530.

4) Jentzsch, K., Krauth, H . , T y i l a s , A., Reiner, J., Schmidt, C., IEEE Transact.

Magn. MAG-17 (1981) 2222.