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SUPERCONDUCTING POLOIDAL COILS FOR THE REACTING PLASMA PROJECT PERFORMANCE TEST OF A MODEL COIL AT A PULSING RATE OF
ABOUT 200 T/s
T. Ogasawara, K. Yasukochi, Y. Kubota, T. Makiura, H. Momota, K. Sato, S.
Yamada, T. Satow, M. Iwamoto, K. Toyoda, et al.
To cite this version:
T. Ogasawara, K. Yasukochi, Y. Kubota, T. Makiura, H. Momota, et al.. SUPERCONDUCTING
POLOIDAL COILS FOR THE REACTING PLASMA PROJECT PERFORMANCE TEST OF A
MODEL COIL AT A PULSING RATE OF ABOUT 200 T/s. Journal de Physique Colloques, 1984,
45 (C1), pp.C1-451-C1-454. �10.1051/jphyscol:1984192�. �jpa-00223748�
JOURNAL DE PHYSIQUE
Colloque C1, supplCment
au noI, Tome 45, janvier 1984 page C1-451
SUPERCONDUCTING POLOIDAL C O I L S FOR THE REACTING PLASMA PROJECT PERFORMANCE TEST OF A MODEL C O I L AT A PULSING RATE OF ABOUT 2 0 0 T / S
T .
Ogasawara,
K .Yasukochi, Y . Kubota,
T .Makiura,
H .~ o m o t a * , K.I. Sato*,
S .
Yamadar,
T .Satow**,
M .Iwamoto**,
K .~ o ~ o d a * * ,
K .Koyama***, T . onishi***, 0 . ~sukamoto' and
T .~ o d a +
College o f Science and Technology, Nihon U n i v e r s i t y , Kanda-Surugadai, Chiyoda-ku, Tokyo 101, Japcm
* ~ n s t i t u t e o f Plasmu Physics, P1agoya U n i v e r s i t y , Furo-cho, Chikusa-ku, Nagoyashi
4 6 4 ,Japan
** M i t s u b i s h i E l e c t r i c Corporation, 1-1-2 Wadasaki-cho, Hyogo-ku, Kobe 662, Japan
***Energy D i v i s i o n , E l e c t r o t e c h n i c a l Laboratory, L'mezono, Sakura-mura, Niihari-gun, Ibaraki 305, Japan
+ ~ a c u l t ~ o f Engineering, Yokohama IJational U n i v e r s i t y , 156 Tokiwadai, Hodogaya-ku, Yokohamashi 240, Japan
Resume - On d e c r i t l ' e t u d e , l a c o n s t r u c t i o n e t l e s e s s a i s d'une bobine supra- c o n d u c t r i c e p u l s e e avec des v a r i a t i o n s de champs t r e s r a p i d e s . Le f o n c t i o n n e - ment en mode p u l s e a e t e obtenu p a r l a decharge d ' u n e c a p a c i t e dans un c i r - c u i t de blocage. En u t i l i s a n t une t e n s i o n aux bornes maximale de 8 kV, on a charge l a bobine j u s q u ' a 4 T avec un t a u x de v a r i a t i o n de 200 T/s. Les p e r t e s e t a i e n t de 0,2 % de l ' e n e r g i e stockee p a r c y c l e . Ces r e s u l t a t s a p p o r t e n t l a d e m o n s t r a t i o n de l a f a i s a b i l i t e de bobines poloTdales s u p r a c o n d u c t r i c e s pour des tokamaks de t a i l l e moyenne.
A b s t r a c t - The design, c o n s t r u c t i o n and t e s t i n g o f a s u p e r c o n d u c t i n g p u l s e c o i l w i t h h i g h f i e l d ramp r a t e s a r e d e s c r i b e d . The p u l s e o p e r a t i o n has been done by a condenser d i s c h a r g e w i t h a clamp c i r c u i t . The c o i l was charged up t o 4 T a t a p u l s i n g r a t e o f 200 T/s by a p p l y i n g t h e maximum t e r m i n a l v o l t a g e o f 8 kV. The a.c. l o s s p e r p u l s e was 0.2 % o f t h e s t o r e d energy. These r e s u l t s demonstrate t h e f e a s i b i l i t y o f superconducting p o l o i d a l c o i l s f o r medium s i z e tokamaks.
The Reacting Plasma P r o j e c t ( R - P r o j e c t ) o f t h e I n s t i t u t e of Plasma Physics, Nagoya U n i v e r s i t y i s d e v e l o p i n g a D-T b u r n i n g , medium s i z e tokamak /I/. Conceptual d e s i g n s t u d i e s have c l a r i f i e d t h e need f o r p o l o i d a l f i e l d (PF) c o i l s w i t h a p u l s i n g r a t e o f a b o u t 100 T/s. I n a t o t a l l y superconducting v e r s i o n o f t h i s tokamak, t h e d e s i g n o f t h e PF c o i l s p r e s e n t s f o r m i d a b l e problems: The r e q u i r e d p u l s e r a t e o f 100 T / s i s r o u g h l y t e n t i m e s h i g h e r t h a n t h a t o f l a r g e s c a l e tokamaks such as NET, ETR, FER and INTOR. S i n c e 1981, t h e R & D team has been engaged i n t h e design, c o n s t r u c t i o n and t e s t of s m a l l - s c a l e model c o i l s /2,3,4/. The o b j e c t i v e i s t o i d e n t i f y t h e c r i t i c a l elements o f t h e d e s i g n and t h e t e c h n o l o g y r e q u i r e d . I n a f i r s t model c o i l , RPC-I, we o b t a i n e d a p u l s e r a t e o f 150 T/s, b u t s u f f e r e d breakdown o f l a y e r t o l a y e r i n s u - r a t i o n / 3 / . The second model c o i l , RPC-11, has been c o n s t r u c t e d w i t h a r e i n f o r c e d i n s u l a t i o n . The d e s i g n c r i t e r i a and t e s t r e s u l t s o f t h i s RPC-I1 a r e presented.
I - CABLED CONDUCTOR
The c o n s t r u c t i o n o f t h e superconducting c a b l e i s i l l u s t r a t e d i n F i g . 1. The main
r e q u i r e m e n t was l o w a.c. l o s s e s a t h i g h p u l s i n g r a t e s , which f o r c e d us t o s t a r t from
a r a t h e r t h i n b a s i c s t r a n d . The s p e c i f i c a t i o n s a r e g i v e n i n T a b l e 1 . The v a r i o u s
l e v e l s a r e t w i s t e d i n o p p o s i t e d i r e c t i o n . The f i r s t l e v e l c o n s i s t s o f t h r e e b a s i c
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984192
Cl-452 JOURNAL DE PHYSIQUE
s t r a n d s and has a t w i s t p i t c h o f 17 mm. I t was compacted by drawing t h r o u g h a d i e r e s u l t i n g i n 3-4 % r e d u c t i o n o f t h e c r o s s s e c t i o n a l area. The second l e v e l c o n s i s t s o f s i x subcables and a CuNi-clad copper w i r e o f 0.65 mm d i a m e t e r and has a p i t c h o f 31 mm. I t was compacted by drawing t h r o u g h a 1.78 mm d i e . The f i n a l c a b l e c o n s i s t s o f 21 subcables t w i s t e d around an i n s u l a t e d SUS s t r i p (0.75 mm x 20 mm) a t a t w i s t i n g p i t c h o f 180 mm. D u r i n g f i n a l c a b l i n g , t h e conductor was compacted by u s i n g a T u r k ' s head machine t o ensure mechanical r i g i d i t y . The f i n i s h e d c a b l e i s 4.1 mm t h i c k and 23.3 mm wide. About 500 m o f c a b l e were produced. I t s c u r r e n t - c a r r y i n g c a p a c i t y a t 4.2 K i s 10 kA i n a f i e l d o f 6 T.
I 1 - MODEL PULSE COIL RPC-I1
T a b l e 2 l i s t s t h e b a s i c parameters o f t h e p u l s e c o i l . The c o i l was wound on a G-11 f o r m e r and forms a s o l e n o i d o f 22 l a y e r s . A f t e r c o m p l e t i o n o f t h e w i n d i n g , many l a y e r s o f w e t bands o f epoxy f i b e r g l a s s were added and cured i n s i t u t o s u p p o r t t h e hoop s t r e s s . S p e c i a l c a r e was needed t o overcome t h e problems o f h i g h v o l t a g e and c r y o g e n i c s t a b i l i t y . The c o i l must w i t h s t a n d a t e r m i n a l v o l t a g e o f a b o u t 10 kV. I n o r d e r t o meet t h i s r e q u i r e m e n t , we have adopted t h e w i n d i n g c o n f i g u r a t i o n shown i n F i g . 2. The narrow s i d e s o f t h e r e c t a n g u l a r c a b l e were covered w i t h an adhesive f i b e r g l a s s tape. Furthermore s i n g l e t u r n s were s e p a r a t e d f r o m one a n o t h e r b y G-10 p l a t e s ( F i g . 2a). The l a y e r t o l a y e r i n s u l a t i o n was ensured b y f i v e Kapton sheets o f 0.25 mm t o t a l t h i c k n e s s . These sheets were p u t between two 0.8 mm t h i c k G-10 spacers t o p r o v i d e c o o l i n g channels i n t h e v e r t i c a l d i r e c t i o n ( F i g . 2b). About 45 % o f t h e s u r f a c e o f t h e c a b l e a r e exposed t o l i q u i d h e l i u m . The c r y o g e n i c s t a b i l i t y o f t h e c o i l s i s m a i n l y determined b y t h e r a t i o o f vapour t o l i q u i d o f h e l i u m i n t h e w i n d i n g d u r i n g t h e p u l s e o p e r a t i o n o f t h e c o i l . The measurements o f a.c. l o s s e s o f a s h o r t sample have been made i n a p u l s i v e f i e l d /2,5/ and t h e l o s s t i m e c o n s t a n t s a t a f i e l d B m = 4 . 0 T a r e g i v e n i n Table 3. From t h e d a t a o f t h e f i n a l c a b l e , we can c a l c u l a t e t h e r a t i o o f vapour t o l i q u i d a t h i g h f i e l d r e g i o n o f t h e c o i l as 25 %.
T h i s i s s m a l l e r t h a n t h e c r i t i c a l v a l u e , 30 %, a t which t h e h e a t t r a n s f e r c h a r a c t e r - r i s t i c s b e g i n t o d e t e r i o r a t e .
111 - EXPERIMENTAL ARRANGEMENT AND TEST RESULTS
F i g u r e 3 shows t h e c r o s s s e c t i o n o f t h e p u l s e c o i l assembled i n a s t a i n l e s s s t e e l c r y o s t a t . S p e c i a l GFRP c a s i n g encloses t h e c o i l i n o r d e r t o a l l o w c a l o r i m e t r i c measurements o f t h e a.c. l o s s e s . R e f i l l i n g o f t h e l i q u i d h e l i u m from t h e o u t s i d e o f t h e c a s i n g can be made b y opening a p l u g . A c a p a c i t o r bank o f a maximum energy o f 600 k J (12 mF, 10 kV) serves as power supply.
The c o i l i s charged up t o a p r e s e n t c u r r e n t i n 18.7 ms f o l l o w i n g a s i n u s o i d a l wave shape and d i s c h a r g e d t o z e r o w i t h t h e h e l p o f a clamp c i r c u i t w i t h a t i m e c o n s t a n t o f a b o u t 50 ms. An example o f t h e wave form i s g i v e n i n F i g . 4. The a.c. l o s s e s p e r p u l s e a r e measured c a l o r i m e t r i c a l l y w i t h a gas f l o w meter and have been p l o t t e d i n F i g . 5 as a f u n c t i o n o f t h e peak f i e l d B, . Note t h a t Bm i s p r o p o r t i o n a l t o t h e p u l s i n g r a t e dB/dt, s i n c e t h e f i e l d r i s e t i m e i s f i x e d . The l o s s p e r p u l s e Q ( J ) versus Bm(T) seems t o f o l l o w a r e l a t i o n ,
Q
=43 Bm 1.7
( 1 ) A p a r a l l e l experiment on t h e a.c. l o s s e s o f a s h o r t sample was done: A sample c o i l wound f r o m 1.5 m o f t h e f i n a l c a b l e was s e t i n t h e bore o f t h e p u l s e magnet and t h e l o s s e s were measured by a s t a n d a r d e l e c t r i c method. These v a l u e s t o g e t h e r w i t h a c a l c u l a t i o n o f t h e f i e l d d i s t r i b u t i o n i n t h e RPC-I1 c o i l were used t o e s t i m a t e t h e t o t a l l o s s o f t h e c o i l . The r e s u l t i s shown by t h e f u l l l i n e i n F i g . 5, which seems t o c o n f i r m t h e observed losses, e q . ( l ) .
I n t h e f i r s t model c o i l RPC-I, t h e breakdown o f l a y e r t o l a y e r i n s u l a t i o n o c c u r r e d a t
a c o i l t e r m i n a l v o l t a g e o f 7.6 kV. I n o r d e r t o c o n f i r m t h e improved c o i l s t r u c t u r e
o f RPC-11, t h e same v o l t a g e was chosen as t h e maximum o p e r a t i o n p o i n t . F i g u r e 6
shows t h e l o a d l i n e o f t h e c o i l RPC-11. As i n d i c a t e d b y t h e c l o s e d c i r c l e , t h e
maximum peak f i e l d was 3.74 T w i t h a peak c u r r e n t o f 4.24 kA and t h e c o i l t e r m i n a l
v o l t a g e o f 7.62 kV. A f t e r f i v e p u l s e o p e r a t i o n s w i t h a r e p e t i o n p e r i o d o f 15 min., t h e c o i l has s u f f e r e d no change i n p u l s i n g c h a r a c t e r i s t i c s . I n F i g . 6, t h e c r i t i c a l c u r r e n t Ic and t h e quenching c u r r e n t i n p u l s e f i e l d s Iq /2/ were e s t i m a t e d f r o m t h e experiments on a 2nd l e v e l subcable. The cold-end r e c o v e r y c u r r e n t i n s t a t i c f i e l d s , I,, observed on t h e f i n a l c a b l e i s a l s o shown.
I V - CONCLUSION
A s m a l l - s c a l e s u p e r c o n d u c t i n g c o i l wound f r o m a l o w l o s s c a b l e d c o n d u c t o r has been t e s t e d . So f a r t h e c o i l was charged up t o a f i e l d o f 3.74 T a t a c o i l t e r m i n a l v o l t a g e o f 7.62 kV. S i n c e t h e waveform o f t h e r i s i n g f i e l d was s i n u s o i d a l w i t h a r i s e - t i m e o f 18.7 ms, t h e average and t h e maximum o f t h e p u l s e r a t e s were 200 T/s and 314 T/s, r e s p e c t i v e l y . The a.c. l o s s i n t h i s p u l s e o p e r a t i o n was 0.23 % o f t h e energy s t o r e d i n t h e c o i l . I n t h e n e x t phase, we i n t e n d t o t e s t t h e c o i l i n a mode o f t h e ohmic h e a t i n g c o i l o f a tokamak machine where t h e f i e l d v e r s u s t i m e has a near1 y t r a p e z o i d a l wave form.
ACKNOWLEDGEMENTS
The a u t h o r s would l i k e t o thank P r o f . H. Kakihana, t h e D i r e c t o r o f t h e I n s t i t u t e o f Plasma P h y s i c s , Nagoya U n i v e r s i t y , f o r encouragement and s u p p o r t o f t h i s work. They a l s o thank Mr. Y. H a t t o r i , Mr. S. Yoshimura, Mr. Y. K a t s u r a , Mr. M. M o r i t a and Mr.
M. Fukushima o f M i t s u b i s h i E l e c t r i c C o r p o r a t i o n f o r v a l u a b l e s u p p o r t t h r o u g h o u t t h e experiments. A p a r t o f t h i s work was supported by t h e G r a n t - i n - A i d f o r F u s i o n Research, t h e M i n i s t r y o f Education.
REFERENCES
1. R - P r o j e c t Design Team, I n s t i t u t e o f Plasma P h y s i c s , Nagoya U n i v e r s i t y , " I n t e r i m R e p o r t on t h e F i r s t Phase Design o f R-Tokamak', Oct. 1981.
2. Ogasawara, T e t a l , Proc. o f t h e ICEC-9 (Kobe, May 1982) p.339.
3. Momota, H. e t a l , Proc. o f t h e ICEC-9 (Kobe, May 1982) p.454.
4. Satow, T. e t a l , IEEE Trans. on Magnetics, MAG-19 (1983) p.1406.
5. Yamada, T. e t a l , Proc. o f t h e ICEC-9 (Kobe, May 1982) p.154.
T a b l e 1 Parameters o f b a s i c s t r a n d T a b l e 3 Loss t i m e c o n s t a n t T a t 4 . 0 1
O u t e r d i a m e t e r 0.35 mn sample r (ms)
F i l a m e n t d i a m e t e r 6.3 ~ u n
b a s i c s t r a n d 0.028
Number o f f i l a m e n t s 760
1 s t l e v e l c a b l e 0.035 T w i s t p i t c h l e n g t h 5.8 mn
2nd l e v e l c a b l e
CuNi o u t e r s h e a t h 15 wn f i n a l c a b l e 0.061
NbTi : Cu : CuNi 1 : 2 : 1 . 6
