LESSONS FROM DESIGN AND MANUFACTURE OF U.S. LCT COILS

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LESSONS FROM DESIGN AND MANUFACTURE OF U.S. LCT COILS

R. Kibbe, P. Haubenreich, C. Gerwig, D. Hackleyr, P. Sangerr, J. Young

To cite this version:

R. Kibbe, P. Haubenreich, C. Gerwig, D. Hackleyr, P. Sangerr, et al.. LESSONS FROM DESIGN

AND MANUFACTURE OF U.S. LCT COILS. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-

125-C1-129. �10.1051/jphyscol:1984127�. �jpa-00223682�

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JOURNAL DE PHYSIQUE

Colloque C l , suppl6ment au no 1, Tome 45, janvier 1984 page CI-131

S T A B I L I T Y TEST RESULT OF THE JAPANESE TEST C O I L FOR THE LARGE C O I L TASK AT THE DOMESTIC TEST

M. N i s h i , T. Ando, T. Hiyama, H. T s u j i , Y . T a k a h a s h i , K. Okuno, K. Yoshida, E. Tada, K. Koizumi, T. K a t o , H. Nakajima, 0 . T a k a h a s h i , M. O s h i k i r i , S. Shimamoto and K. Yasukochi

Fusion Research Center, Japan Atomic Energy Research I n s t i t u t e , Mukaiyama, Naka-Machi, Naka-Gun, Ibaraki-Ken,

311-02,

Japan

Rdsum6

-

La c o n c e p t i o n de l a b o b i n e j a p o n a i s e LCT, d t a i t b a s d e a u d 6 p a r t

2iF-E

c r i t s r e d e s t a b i l i t d d i t d e " r d c u p 6 r a t i o n a v e c une e x t r d m i t b

f r o i d e " . Ndanmoins, p a r s u i t e d e s dbveloppements a p p o r t d s s u r l a s u r f a c e d e r e f r o i d i s s e m e n t du c o n d u c t e u r , l a b o b i n e d d f i n i t i v e p e u t s t r e c o n s i d d r 6 e c o m e r e m p l i s s a n t l e s c o n d i t i o n s d e s t a b i l i t d i n c o n d i t i o n n e l l e s , s u p b r i e u r e 1 c e l l e d e l ' e x t r d m i t b f r o i d e . C e t t e s t a b i l i t 6 e s t c o n f i r m b e p a r l e s r d s u l t a t s d e s t e s t s e t une a n a l y s e d b t a i l l d e . La marge d e c o u r a n t d a n s l e s c o n d i t i o n s n o m i n a l e s d e f o n c t i o n n e m e n t e s t e s t i m 6 e

B

e n v i r o n 22 %.

A b s t r a c t - The d e s i g n i n g work of t h e J a p a n e s e LCT c o i l was begun b a s e d on t h e c o l d end r e c o v e r y c r i t e r i o n . B u t , a s t h e r e s u l t o f r e s e a r c h and

development work on t h e c o n d u c t o r ' s c o o l i n g s u r f a c e , t h e completed c o i l was e s t i m a t e d t o be i n t h e u n c o n d i t i o n a l r e c o v e r y r e g i o n more s t a b l e t h a n t h e c o l d end one. T h i s i s v e r i f i e d i n t h i s p a p e r by t h e r e s u l t s of t h e d o m e s t i c t e s t and t h e d e t a i l e d a n a l y s i s . The e s t i m a t e d c u r r e n t m a r g i n a t t h e nominal o p e r a t i n g c o n d i t i o n i s a b o u t 22%.

J a p a n Atomic Energy R e s e a r c h I n s t i t u t e c a r r i e d o u t t h e d o m e s t i c t e s t o f t h e J a p a n e s e LCT c o i l and showed t h a t t h e c o i l s a t i s f i e d i t s a l l d e s i g n c r i t e r i a t h a t c o u l d be c o n f i r m e d by t h e s i n g l e c o i l t e s t / l / . The s t a b i l i t y c r i t e r i o n f o r t h e LCT c o i l s s p e c - i f i e d by Oak Ridge N a t i o n a l L a b o r a t o r y i s " t o r e c o v e r f u l l y s u p e r c o n d u c t i n g s t a t e f o l l o w i n g t h e o c c u r r e n c e of a h a l f t u r n l e n g t h n o r m a l c y " . I n c a s e of t h e J a p a n e s e c o i l , t h e c o n d i t i o n s f o r t h i s c r i t e r i o n a r e t h e t r a n s p o r t c u r r e n t o f 1 0 . 2 2 kA, t h e a v e r a g e c u r r e n t d e n s i t y i n winding of 26.6 ~ / m m ~ , t h e m a g n e t i c f i e l d o f 8 T and t h e p o o l c o o l i n g . To g e t h i g h s t a b i l i t y , low ohmic h e a t g e n e r a t i o n and h i g h c o o l i n g ca- p a c i t y a r e d e s i r e d f o r t h e c o n d u c t o r . The f o r m e r depends upon t h e q u a n t i t y and t h e e l e c t r i c a l r e s i s t i v i t y o f t h e s u b s t r a t e . I n c a s e of t h e J a p a n e s e LCT c o n d u c t o r , t h e y were a l m o s t d e t e r m i n e d by t h e m e c h a n i c a l r e q u i r e m e n t on t h e c o n d u c t o r and by t h e p r o p e r t i e s o f Cu, a n d , t h e c o o l i n g c a p a c i t y o v e r 0.7 w/cm2 was r e q u i r e d f o r t h e con- d u c t o r ' s c o o l i n g s u r f a c e . A f t e r t h e s t u d y o f many k i n d s of s u r f a c e s on t h e i r h e a t t r a n s f e r c h a r a c t e r i s t i c s / 2 / , we d e v e l o p e d t h e o x i d i z e d roughened s u r f a c e / 3 / whose e q u a l a r e a h e a t f l u x i s s u f f i c i e n t l y h i g h t o s t a b i l i z e t h e J a p a n e s e LCT c o i l , a n d , t h e s t r u c t u r e o f t h e c o n d u c t o r was d e t e r m i n e d a s shown i n F i g . 1 and T a b l e 1 . The c o o l i n g c a p a c i t y of t h e d e v e l o p e d s u r f a c e i s v e r y h i g h , s o , i t was p r e a n a l i z e d t h a t t h e c o i l was i n more s t a b l e r e g i o n t h a n t h e c o l d end r e c o v e r y one.

I n t h i s p a p e r , we d e s c r i b e t h e method and r e s u l t s o f t h e a n a l y s i s a t f i r s t , and p r e s e n t t h e r e s u l t s of t h e d o m e s t i c t e s t .

T a b l e 1. Major p a r a m e t e r s o f t h e J a p a n e s e LCT c o n d u c t o r F i g . 1

8T-conductor 5T-conductor The c r o s s -

O v e r a l l d i m e n s i o n s 1 2 . 6 x 2 6 . 8 12.6 x 21.3 mm s e c t i o n of

Cu/Superconductor r a t i o 7.28 7 . 4 1 t h e 8T-

E f f e c t i v e Cu a r e a 227 196 mm2 c o n d u c t o r .

A v a i l a b l e C o o l i n g S u r f a c e 3.47 2.70 cm2/cm

Rated C u r r e n t 10.22 10.22 k A

C u r r e n t D e n s i t y

( C o n d u c t o r ) 30.3 38.1 ~ / m m ~

(Winding) 24.2 3 0 . 3 ~ / m m ~

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984127

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C1-132 JOURNAL DE PHYSIQUE

I - STABILITY ANALYSIS

There i s v e r y s i m p l e c r i t e r i o n / 4 / t o d e s i g n a s t a b l e c o i l , b u t when t h e s t a b i l i t y of a completed c o i l i s t e s t e d , a d e t a i l a n a l y s i s which s i . n u l a t e s w e l l t h e c o n d i t i o n of t h e c o i l must be done i n o r d e r t o e v a l u a t e t h e o b t a i n e d d a t a c o r r e c t l y . T h i s i s p a r - t i c u l a r l y n e c e s s a r y i n c a s e t h a t t h e change o f t h e c o n d i t i o n a l o n g t h e c o n d u c t o r i s s t r o n g l i k e t h e LCT c o i l . To a n a l i z e t h e s t a b i l i t y o f t h e J a p a n e s e LCT c o i l , we s o l v e d n u m e r i c a l l y one d i m e n s i o n a l h e a t f l o w e q u a t i o n a s f o l l o w s ;

where t i s t i m e , x i s d i s t a n c e a l o n g c o n d u c t o r , T, p , C and A a r e t e m p e r a t u r e , d e n s i - t y , s p e c i f i c h e a t and t h e r m a l c o n d u c t i v i t y of t h e c o n d u c t o r r e s p e c t i v e l y . Qj i s t h e o h m i c a l l y g e n e r a t e d h e a t , Qd i s t h e d i s t u r b a n c e h e a t , Qh i s t h e h e a t t r a n s r e r e d t o t h e l i q u i d helium and Qn i s t h e h e a t c o n d u c t e d t o t h e n e i g h b o u r i n g t u r n s .

I n t h e e x p e r i m e n t , t h e d i s t u r b a n c e h e a t i s poured by t h e h e a t e r i n t o t h e c o n d u c t o r , s o , i n t h e p r e s e n t a n a l y s i s , t h e s p e c i f i c h e a t o f t h e h e a t e r and t h e t h e r m a l r e s i s t - ance between t h e h e a t e r and t h e c o n d u c t o r were c o n s i d e r e d . I n t h e t e s t z o n e , by t h e d e c r e a s e of t h e s u b s t r a t e due t o t h e i n s t a l l a t i o n o f

t h e h e a t e r , t h e s t a b i l i t y l i m i t i s e s t i m a t e d t o be

12.4 kA - 8 T, w h i l e t h a t o f t h e c o n d u c t o r w i t h no @esi cw\~ng Curve h e a t e r s i s c a l c u l a t e d t o be 12.7 kA - 8 T/3/.

I n c a s e o f t h e J a p a n e s e LCT c o i l , t h e c o o l i n g c h a n n e l

$

'.O-

made by t h e s p a c e r s between pancakes changes i t s o r i e n -

x

^0,8. Worst Cooling Curve t a t i o n a l o n g t h e c o n d u c t o r . According t o t h i s c h a n g e , 2

t h e c o o l i n g c h a r a c t e r i s t i c s of t h e c o n d u c t o r ' s c o o l i n g

'

^0.6-

s u r f a c e change a l o n g t h e c o n d u c t o r . F i g . 2 shows t h e (6.4T-i0220Al . c o o l i n g c u r v e s measured a t t h e model t e s t and t h e h e a t

g e n e r a t i o n c u r v e s . The b e s t c o o l i n g c u r v e a p p e a r s a t 0.2- t h e t o p and t h e bottom p a r t s o f t h e c o i l , a n d , t h e con-

d u c t o r s i n t h e v e r t i c a l o r i e n t a t i o n have t h e w o r s t one.

Even t h e ohmic g e n e r a t i o n h e a t f l u x a t 10.22 kA - 8 T T conductor - T L . H ~ Ldeg) i s lower t h a n t h e minimum f i l m b o i l i n g h e a t f l u x o f t h e

w o r s t . c o o l i n g c u r v e , t h a t i s , t h e c o i l i s i n uncondi- F i g ' 2 Steady s t a t e

t i o n a l r e c o v e r y r e g i o n everywhere. h e l i u m h e a t t r a n s f e r c h a r a c - t e r i s t i c s o f t h e c o n d u c t o r ' s The map of t h e s t a b i l i t y f a c t o r a l o n g t h e c o n d u c t o r of c o o l i n g s u r f a c e and ohmic t h e c e n t r a l p a n c a k e ' s i n n e r m o s t t u r n c a l c u l a t e d from h e a t g e n e r a t i o n c u r v e s . t h e c o o l i n g c h a r a c t e r i s t i c s and t h e m a g n e t i c f i e l d i s

shown i n F i g . 3 . The h i g h e s t v a l u e , t h e l o w e s t s t a b i l i t y , a p p e a r s a t t h e node 330 a t t h e s i n g l e c o i l t e s t and a t t h e node 370 a t t h e s i x c o i l t e s t where t h e m a g n e t i c f i e l d i s t h e s t r o n g e s t i n e a c h c a s e . The d e n t between n o d e s 100 and 300 i s due t o t h e good c o o l i n g c h a r a c t e r i s t i c s .

F i g . 4 shows t h e c a l c u l a t e d t e m p e r a t u r e p r o f i l e s on t h e c o n d i t i o n t h a t t h e c o i l i s i n

NOOE NO.

1 node l e n g t h is 1 crn

Normal Condition at &coil Test

0.6 a U

0.4 100% Charged State

I-

;

0.2 at the Domestic Test

NOOE NUMBER

F i g . 3 Map o f s t a b i l i t y f a c t o r a l o n g t h e c o n d u c t o r o f t h e c e n t r a l p a n c a k e ' s i n n e r - most t u r n . Qj i s t h e ohmic g e n e r a t i o n h e a t f l u x and Qeq i s t h e e q u a l a r e a h e a t f l u x .

HEATFD ZONE

Fig.4 C a l c u l a t e d t e m p e r a t u r e p r o f i l e s a f t e r 0 . 2 sec-0.75 m h e a t i n g a t t h e s i n g l e 100% c h a r g e d s t a t e .

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s i n g l e 100% c h a r g e d s t a t e ( 1 0 . 2 2 kA - 6.4 T ) and t h e 0 . 7 5 m l o n g t e s t zone i s h e a t e d . Because of t h e t h e r m a l r e s i s t a n c e between t h e h e a t e r and t h e c o n d u c t o r , i t t a k e s r a t h e r l o n g t i m e t o r e c o v e r p e r f e c t l y . The t e m p e r a t u r e r i s e s f a s t e r and r e m a i n s l a t e r where t h e d e g r e e o f s t a b i l i t y i s l o w e r . T h i s r e s u l t shows t h a t t h e r e c o v e r y which l o o k s l i k e t h e c o l d end one can be s e e n even i n t h e u n c o n d i t i o n a l r e c o v e r y r e g i o n due t o t h e d i f f e r e n c e of t h e s t a b i l i t y d e g r e e a l o n g t h e c o n d u c t o r .

I11

-

VERIFICATION OF THE UNCONDITIONAL RECOVERY

F i g . 6 Measured dependency of The t y p e o f t h e r e c o v e r y s e e n a t t h e d o m e s t i c t e s t

normalcy,s l i f e time in t h e i s t h e u n c o n d i t i o n a l one. T h i s i s v e r i f i e d by

r e g i o n between v o l t a g e t a p s

F i g s . 6 and 7 . on i t s l e n g t h a t t h e 100%

I1 - TEST PROCEDURE AND RESULTS Heated Zone

I n t h e J a p a n e s e LCT c o i l , t h e r e a r e 16 h a l f t u r n t e s t zones where h e a t - G V e r a , h i g h s p e e d c a r b o n t h i n f i l m

$2

t e m p e r a t u r e s e n s o r s and v o l t a g e t a p s

- -

a r e i n s t a l l e d on t h e c o n d u c t o r . To Z Z i n s u l a t e from t h e c o n d u c t o r e l e c t r i -

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c a l l y , t h e r e a r e r a t h e r t h i c k i n s u -

g z

l a t o r s around h e a t e r s which p l a y a s

t h e t h e r m a l b a r r i e r s i m u l t a n e o u s l y

.

^% F i g . 5 Measured

T h i s b a r r i e r d u l l s t h e h e a t p u l s e

5 %

v o l t a g e and

which i s i n p u t t o t h e c o n d u c t o r from

g 2

t e m p e r a t u r e

t h e h e a t e r . So i t was i m p o s s i b l e t o

? z

p r o f i l e s a f t e r

examine a b o u t t h e t r a n s i e n t s t a b i l i - a h a l f t u r n

t y and we t o o k t h e method t o o b s e r v e h e a t i n g a t t h e

t h e normalcy c r e a t e d on t h e conduc- 100% c h a r g e d

t o r by t h e s u f f i c i e n t h e a t . s t a t e .

TIME (200 msec/dw) The h e a t i n g power was d e t e r m i n e d t o

r a i s e t h e t e m p e r a t u r e o f t h e c o n d u c t o r a l i t t l e above t h e c r i t i c a l v a l u e o f t h e su- p e r c o n d u c t o r f o r each h e a t e r a t t h e c o i l c u r r e n t o f z e r o and was f i x e d d u r i n g t h e s t a b i l i t y t e s t . T y p i c a l h e a t i n g powers a r e 350 J/m - 0.2 s e c f o r h e a t i n g l e s s t h a n a h a l f t u r n and 470 J/m - 0 . 4 s e c f o r a h a l f t u r n h e a t i n g .

The s t a b i l i t y t e s t was c a r r i e d o u t from t h e low c h a r g e d s t a t e and t h e s h o r t l e n g t h h e a t i n g up t o a h a l f t u r n l e n g t h h e a t i n g a t t h e 100% c h a r g e d s t a t e (10.22 kA, 6 . 4 T , 106 MJ). The t o t a l number o f h e a t i n g was 207 and a l l t h e d a t a o f v o l t a g e and tempera- t u r e were t a k e n i n t h e PDP 11/70 d a t a a c q u i s i t i o n s y s t e m . Any u n s t a b l e b e h a v i o r c o u l d n o t be s e e n i n t h e c o i l d u r i n g t h e t e s t and a l l n o r m a l c i e s c r e a t e d by h e a t e r s d i s a p - p e a r e d s p o n t a n e o u s l y and p e r f e c t l y .

F i g . 5 shows t h e v o l t a g e and t h e t e m p e r a t u r e p r o f i l e s a f t e r h e a t i n g a h a l f t u r n l e n g t h t e s t zone i n c l u d i n g t h e s t r o n g e s t m a g n e t i c f i e l d p o i n t a t t h e 100% c h a r g e d s t a t e . The h e a t i n g power was 2 . 3 k J - 0.4 s e c which c o r r e s p o n d s t o 1.7 ~ / c m ~ p e r u n i t volume o f t h e c o n d u c t o r . The t e m p e r a t u r e o f t h e c o n d u c t o r began t o r i s e g r a d u a l l y j u s t a f t e r t h e s t a r t of t h e h e a t i n g , a n d , a b o u t 0.2 second l a t e r , t h e y s t o o d up s u d d e n l y which was t h o u g h t t o be t h e t r a n s i t i o n from t h e n u c l e a t e b o i l i n g t o t h e f i l m b o i l i n g . The maximum t e m p e r a t u r e a p p e a r e d on t h e c o n d u c t o r was a b o u t 20 K. About t h e same t i m e w i t h t h e s t a n d i n g up o f t h e t e m p e r a t u r e , t h e v o l t -

-

The l i f e t i m e of t h e normalcy depends on i t s l e n g t h c h a r g e d s t a t e . a g e s a p p e a r e d . The o h m i c a l l y g e n e r a t e d h e a t i n t h e

g 2

c o n d u c t o r c a l c u l a t e d from t h e t r a n s p o r t c u r r e n t and

.11.

t h e a p p e a r e d v o l t a g e was a b o u t 920 W (1.1 ~ / c m 3 ) . >

The c r e a t e d normalcy began t o d i s a p p e a r from t h e c e n t e r o f t h e h e a t e d zone where t h e d e g r e e of s t a - k I 1

2

b i l i t y was e s t i m a t e d t o be t h e h i g h e s t . W i t h i n 2 s e c o n d s a f t e r t h e s t a r t of h e a t i n g , t h e normalcy

2

d i e d o u t i n c o u r s e o f t i m e p e r f e c t l y and t h e c o i l was proved t o be s t a b l e a g a i n s t a h a l f t u r n l e n g t h

- ' ' ' ' ' -

. V H 3 3 - 3 4 ( 0 7 B m )

-

^-

I

~ ~ 2 7 - 2 8 10 71 rn I

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* = = .

^-

- V H 3 0 - 3 1 1 0 8 8 m l -

-

- ,

,

, Heotlng , , Tlme

,

200rnsec ,

,

, -

normalcy a t t h e 100% c h a r g e d s t a t e .

L"

A OO 1 2 3 4 5

LENGTH OF NORMALCY

( m )

(5)

CI-134 JOURNAL DE PHYSIQUE

~ O ~ I I I I I , Ii n c a s e o f t h e c o l d end r e c o v e r y . But t h i s depend- -

-

> H z n g Calculated Curve e n c y c o u l d n o t be s e e n a t t h e d o m e s t i c t e s t a s

6

15- shown i n F i g . 6 .

F i g . 7 shows t h e m e a s u r e d v o l t a g e p r o f i l e a f t e r h e a t i n g t h e t e s t z o n e b e t w e e n ~ ~ 2 7 - 2 8 a t t h e 1 0 0 % c h a r g e d s t a t e w i t h t h e c a l c u l a t e d o n e . The c a l c u l a - t i o n was b a s e d on t h e a s s u m p t i o n t h a t t h e c o i l i s 1603 i n u n c o n d i t i o n a l r e c o v e r y r e g i o n b u t h a s t h e d i s - T I M E (msecl t r i b u t i o n o f t h e s t a b i l i t y d e g r e e a s d e s c r i b e d f o r - F i g . 7 Measured a n d c a l c u l a t e d m e r l y . The two c u r v e s a g r e e v e r y w e l l , s o t h e a s - v o l t a g e p r o f i l e s b e t w e e n ~ ~ 2 7 - s u m p t i o n i s p r o v e d t o b e c o r r e c t .

28 a f t e r heating this 0 ' 7 1 From t h e s e f a c t s , we c a n s a y t h a t t h e c o i l was i n

'One at t h e l o o % charged s t a t e ' u n c o n d i t i o n a l r e c o v e r y r e g i o n a t t h e d o m e s t i c t e s t . I V - ESTIMATION OF STABILITY LIMIT

The v o l t a g e s h r l n k v e l o c i t y shown i n F i g . 8 a r i s e s due t o t h e d i f f e r e n c e o f t h e d e g r e e o f s t a b i l i t y a l o n g t h e c o n d u c t o r and i s d i f f e r e n t from t h e n o r m a l f r o n t ve-

rcEj

- 2 l o c i t y d e f i n e d i n t h e c o l d e n d r e c o v e r y r e g i o n . But t h e s t a b i l i t y l i m i t c a n be e s t i m a t e d by t h i s v o l t a g e s h r i n k

g2-4

v e l o c i t y b e c a u s e i t a l s o d e p e n d s on t h e s t a b i l i t y . The

*

^{- 6}

e s t i m a t e d s t a b i l i t y l i m i t from F i g . 8 i s a b o u t 1 2 3 % ₀UJ -8

which means t h e t r a n s p o r t c u r r e n t o f 1 2 . 6 kA and t h e

2

^V,=(distance between taps1 / t m a g n e t i c f i e l d o f 7 . 9 T. T h i s v a l u e i s i n good a g r e e -

&

_- -loO 2 0 4 0 6 0 8 0 100 1 2 0 1 4 0 ment w i t h t h e c a l c u l a t e d o n e ( 1 2 . 4 kA - 8 . 0 T I . T h e r e - CHARGE STATE ( % 1 f o r e , t h e J a p a n e s e LCT c o i l i s e s t i m a t e d t o be s t a b l e

F i g . 8 V o l t a g e s h r i n k a t t h e n o r m a l o p e r a t i n g c o n d i t i o n a t t h e s i x c o i l t e s t

velocity measured between

( 1 0 . 2 2 kA - 8 . 0 T ) w i t h t h e c u r r e n t m a r g i n e o f 2 2 % .

v o l t a g e t a p s a t a h a l f

v

- C O N C L U S I ~ N S t u r n h e a t i n g .

S t a b i l i t y t e s t was c a r r i e d o u t on t h e J a p a n e s e LCT c o i l a t t h e d o m e s t i c t e s t . A h a l f t u r n n o r m a l c y c r e a t e d by t h e h e a t e r a t t h e 100% c h a r g e d s t a t e ( 1 0 . 2 2 kA, 6 . 4 T , 106 MJ) d i s a p p e a r e d s p o n t a n e o u s l y and t h e c o i l was p r o v e d t o be s t a b l e . The t e s t r e s u l t s were i n good a g r e e m e n t w i t h t h e c a l c u l a t e d o n e . R e s u l t s a r e summarized a s f o l l o w s ;

1 ) The c o i l was i n t h e u n c o n d i t i o n a l r e c o v e r y r e g i o n a t t h e d o m e s t i c t e s t a s was p r e l i m i n a r y e s t i m a t e d a n d i s e x p e c t e d t o be i n t h e same r e g i o n a t t h e n o r m a l o p e r - a t i n g c o n d i t i o n a t t h e s i x c o i l t e s t ( 1 0 . 2 2 kA - 8 . 0 T ) .

2 ) The s t a b i l i t y l i m i t o f t h e c o i l i s e s t i m a t e d t o be a b o u t 1 2 . 5 kA

-

8 T b o t h ex- p e r i m e n t a l l y and a n a l y t i c a l l y w h i c h c o r r e s p o n d s t o t h e c u r r e n t m a r g i n o f a b o u t 22%

a t t h e n o r m a l o p e r a t i n g c o n d i t i o n a t t h e s i x c o i l t e s t .

These good r e s u l t s on s t a b i l i t y a r e m a i n l y due t o t h e d e v e l o p e d o x i d i z e d r o u g h e n e d c o d l i n g s u r f a c e . And owing t o p l e n t y o f d a t a f r o m t h e t e s t s c a r r i e d o u t b e f o r e a n d d u r i n g m a n u f a c t u r e of t h e c o i l , t h e a c c u r a c y o f t h e a n a l y s i s was much r a i s e d . From t h e s e , r e s u l t s , much l a r g e r p o o l - c o o l e d s t a b l e c o i l s c a n b e d e s i g n e d a s f a r as t h e s t a b i l i t y c o n c e r n e d .

ACKNOWLEDGEMENTS

The a u t h o r s would l i k e t o t h a n k D r s . S . M o r i , Y . I s o and Y.Obata f o r t h e i r c o n t i n u o u s e n c o u r a g e m e n t . The c o m p a n i e s r e l a t e d t o t h i s p r o j e c t a r e g r a t e f u l l y a c k n o w l e d g e d . REFERENCES

1. Shimamoto, S . e t a l . , "Domestic T e s t R e s u l t o f t h e J a p a n e s e LCT C o i l " , IEEE T r a n s . Magn., V o l . MAG-19, No.3, pp.851-858 ( 1 9 8 3 )

2. N i s h i , M . ' e t a l . , " H e a t T r a n s f e r C h a r a c t e r i s t i c s o f t h e L a r g e S u p e r c o n d u c t o r s w i t h D i f f e r e n t S u r f a c e C o n d i t i o n s ( i n J a p a n e s e ) " , JAERI-M 8 7 7 1 ( 1 9 8 0 )

3. N i s h i , M. e t a l . , "Roughened S u r f a c e S t u d y on J a p a n e s e T e s t C o i l f o r t h e L a r g e C o i l T a s k " , IEEE T r a n s . Magn., V o l . MAG-17, No.1, pp.904-907 ( 1 9 8 1 )

4. Maddock, B. J . e t a l . , " S u p e r c o n d u c t i v e C o m p o s i t e s : H e a t T r a n s f e r a n d S t e a d y S t a t e S t a b i l i z a t i o n " , C r y o g e n i c s

9,

pp.261-273 ( 1 9 6 9 )