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DEVELOPMENT AND TEST RESULTS OF A 4MJ-CLASS PULSED SUPERCONDUCTING
MAGNET
H. Tateishi, T. Onishi, K. Komuro, K. Koyama, M. Kawashima, C. Suzawa
To cite this version:
H. Tateishi, T. Onishi, K. Komuro, K. Koyama, M. Kawashima, et al.. DEVELOPMENT AND TEST RESULTS OF A 4MJ-CLASS PULSED SUPERCONDUCTING MAGNET. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-455-C1-458. �10.1051/jphyscol:1984193�. �jpa-00223749�
JOURNAL DE PHYSIQUE
Colloque C I , supplkment au no 1, Tome 45, janvier 1984 page CI-455
DEVELOPMENT AND TEST RESULTS OF A 4MJ-CLASS PULSED SUPERCONDUCTING MAGNET
H. Tateishi, T. Onishi, K. Komuro, K. Koyama, M. ~awashima* and C. ~uzawa*
ELectrotechnicaZ Laboratory, Japan
*Swnitorno Electric Industries, Ltd., Japan
Resum6 - Un aimant supraconducteur pulse d'energie s t o c k 6 e d e 4MJ a Bt6 construit e t m i s en c h a r g e avec s u c c e s en regime continu. P o u r u n courant maximum d e 5 5 0 0 a m p e r e s , l e c h a m p magn6tique maximum est 6.4T, le champ a u c e n t r e e s t de 5.8T, et 1'6nergie a c c u m u l e e e s t d e 4.OMJ. Le c o n d u c t e u r d e l'aimant est stabilise p a r d e l'aluminium d e h a u t e puret6. L'aimant se compose d e 12 enroulements B double g a l e t t e , les d i a m e t r e s i n t e r i e u r , exterieur et l a hauteur s o n t respectivement d e 5 0 0 m m , 9 5 6 m m e t 6 2 6 mm.
D a n s l'essai en courant c o n t i n u , l e courant d e p o i n t e a 6 t e augment6 graduellement un t a u x d e vitesse c o n s t a n t e , e t finalernent l'aimant a 6 t B m i s e n charge jusqu'a 5 5 2 0 a m p e r e s en e n v i r o n 8 0 secondes.
Abstract - A pulsed superconducting magnet with a stored energy of 4 MJ has been constructed and successfully charged in dc operation. At the maximum ope- rating current of 5500 amps, the maximum field is 6.4 T, the central field is 5.8 T and the stored energy is 4.0 MJ. The conductor for the magnet is stabi- lized with high purity aluminium. The magnet consists of 12 double pancake coils and has an inner diameter, outer diameter and height of 500 mm, 958 mm and 626 nun, respectively. At the dc test, the peak current was gradually in- creased at the constant ramp rate and finally the magnet was charged up to 5520 amps in about 80 seconds.
INTRODUCTION
A development program of a pulsed superconducting magnet aiming at the ohmic heating coil of the tokamak reactor was started in 1978 at ETL. In the first three years, we developed and tested two 70kJ-class magnets/l/ and
two 400kJ-class magnets/2,3/. As a next step we decided to & ~ i - c l a d s t r a n d
f 4 0 3 ~ )
develop a MJ-class pulsed magnet. It should be designed for
cuNi s , c s t rand
a cryostability, high overall current density and low ac cu . .
losses. To achieve these purposes, we adopted high purity ~ b r i
aluminium as the stabilizer and CuNi-sheathed basic strands.
In this paper, the conductor structure, fabrication of the magnet and dc test results are described.
CONDUCTOR STRUCTURE
I r s t - l e v e l a b l e
The conductor for the magnet is a three-stage twisted cable designed for a cryostability, high current density and low losses. A schematic of tine cross section of the conductor Kapton is illustrated in Fig.1. A basic superconducting strand is
CuNi-sheathed to reduce interstrand coupling losses/4/. The CuNi
1st-level subcable is fabricated by twisting four basic strands and three 5-9's grade high purity aluminium wires.
These wires are solder-filled to improve current sharing characteristics and mechanical regidity. The 2nd-level subcable is assembled by twisting six 1st-level
F l p . 1 Schematic of c a b l e cross section.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984193
Cl-456 JOURNAL DE PHYSIQUE
Table 1 Parameters o f the maqnet Coil
Winding i.d.
Winding o-d.
Winding height Total turns Cable length Total weight Cable weiqht Inductance IOP
J o ~ , o v e r a l l
Stored energy
12 double pancakes 500 nrm 958 mm 6 2 6 mm 792 1810 m 1770 kg 1100 kg 0.26 H 5500 A 30.4 ~ / m m ~ 5.8 T 6.4 T
4.0 M J F 1 9 . L Cable contraction due t o compreaslve f o r c e P.
F ~ g . 3 D o u b l e pancake structure.
Arrows s h o w f l o w pattern o f hcllum bubble.
s u b c a b l e s a r o u n d a n i n s u l a t e d CuNi w i r e . T h e f i n a l c a b l e i s composed o f 1 5 2nd- l e v e l s u b c a b l e s . They a r e t w i s t e d a r o u n d a s t a i n l e s s s t e e l s t r i p i n s u - l a t e d by Kapton t a p e . F i n a l l y , Nomex t a p e i s gap-wrapped o n t h e f i n a l c a b l e t o s e r v e n o t o n l y a s t h e t u r n t o t u r n i n s u l a t i o n b u t a s a x i a l c o o l i n g c h a n n e l .
MAGNET FABRICATION
The m a g n e t c o n s i s t s o f 1 2 d o u b l e p a n c a k e c o i l s . Main p a r a m e t e r s a r e l i s t e d i n T a b l e 1. S i n c e t h e c o n d u c t o r i t s e l f c a n n o t e n d u r e t h e e l e c t r o m a g n e t i c f o r c e o f t h e magnet when it i s e n e r g i z e d , a n o t h e r s t a i n l e s s s t e e l s t r i p i s co-wound w i t h t h e con- d u c t o r f o r a n a d d i t i o n a l s u p p o r t member.
F i g . 2 shows t h e c o n t r a c t i o n o f t h e c o n d u c t o r d u e t o c o m p r e s s i v e l o a d c o r r e s p o n - d i n g t o a x i a l f o r c e . The s a m p l e c o n f i g u r a t i o n i s a l s o i l l u s t r a t e d i n t h e f i g u r e . I n t h i s c o n f i g u r a t i o n , m o s t o f t h e l o a d w i l l b e p u t on t h e o u t e r s t a i n l e s s s t e e l s t r i p . The r e s u l t shows t h a t t h e v i r t u a l ~ o u n g ' s modulus is v e r y s m a l l i n l o w stress r e g i o n b e t w e e n p o i n t s A a n d 0 i n t h e f i g u r e . Whereas, t h e a x i a l f o r c e i s 500 t o n s a t t h e c e n t r a l p a n c a k e c o i l s a n d t h i s i s e q u i v a l e n t t o t h e p o i n t P a x i a l i n t h e f i g u r e . T h e r e f o r e t h e c o n d u c t o r h a s t o b e p r e - c o m p r e s s e d t o d o a t l e a s t . To c a r r y o u t t h i s
' p r e - c o m p r e s s i o n ' , o f t h e m a g n e t , t h e a x i a l s u p p o r t p l a t e i s d e s i g n e d t o b e movable a x i a l l y , w h i c h i s shown i n F i g . 3 . v c h d o u b l e p a n c a k e c o i l was c o m p r e s s e d w i t h a f o r c e o f 5 0 0 t o n s a f t e r t h e w i n d i n g was f i n i s h e d a n d t h e magnet i t s e l f was a l s o com- p r e s s e d w i t h t h e same f o r c e a f t e r i t was s t a c k e d . F i g . 3 a l s o shows t h e c o o l i n g chan- n e l o f e a c h d o u b l e p a n c a k e c o i l . When t h e m a g n e t i s c h & g e d , h e l i u m b u b b l e s a r e gen- e r a t e d i n w i n d i n g s d u e t o a c l o s s e s . They a r e g u i d e d t o a x i a l c o o l i n g c h a n n e l by a b u b b l e s e p a r a t i n g p l a t e i n t h e f i g u r e . They f i n a l l y c l i m b u p t o a t o p f l a n g e a n d a r e e x p e l l e d t o t h e o u t s i d e o f t h e m a g n e t .
We m e a s u r e d t h e a c l o s s e s o f t h e f i n a l c a b l e by a n e l e c t r i c method a n d o b t a i n e d a v a l u e o f 1.4ms a s t h e c o u p l i n g t i m e c o n s t a n t . U s i n g t h i s v a l u e a n d c o n s i d e r i n g t h e f i e l d p r o f i l e o f t h e m a g n e t , t h e t o t a l l o s s e s a r e e s t i m a t e d t o b e 0 . 1 3 % o f t h e s t o r e d e n e r g y f o r a b i p o l a r sweep f r o m -6T t o +6T i n 2 s e c o n d s . However, f r o m t h e r e s u l t s o f s u b s e q u e n t m e a s u r e m e n t s , we i n f e r t h a t t h e c o u p l i n g t i m e c o n s t a n t i s l e s s t h a n 1.4ms, t h o u g h a p r e c i s e v a l u e h a s n o t y e t b e e n d e c i d e d . S o t h e t o t a l l o s s e s m i g h t b e l o w e r t h a n t h i s e s t i m a t i o n .
DC TEST OF THE MAGNET 1. COOL DOWN
F i g . 4 shows t h e c o o l down p r o c e s s o f t h e e x p e r - i m e n t . T e m p e r a t u r e s o f some p a r t s o f t'ne m a g n e t mea- s u r e d by t h e r m o c o u p l e s a n d a c o i l r e s i s t i v i t y a r e p l o t t e d . T h e i r l o c a t i o n s a r e shown i n t h e f i g u r e , t o o . They a r e a t t a c h e d o n t h e s u r f a c e o f FRP s p a c e r s i n s e r t e d b e t w e e n d o u b l e p a n c a k e c o i l s .
F i r s t , n i t r o g e n g a s was c i r c u l a t e d a r o u n d t h e magnet f o r a b o t 20 h o u r s . Then, l i q u i d n i t r o g e n was p o u r e d i n t o a c r y o s t a t a n d t h e magnet was immersed
~ i q . 4 cool down process
i n t h e l i q u i d i n a b o u t 5 h o u r s and we l e t am i t a s l t was f o r 1 2 h o u r s . T h e n , t h e a l i q u i d was blown o u t o f t h e c r y o s t a t and - ,
we s t a r t e d t h e t r a n s f e r o f l i q u i d h e l i u m . g-,oo
A f t e r 6 h o u r s , t h e magnet became s u p e r - -
conductive. F i n a l l y , I n 1 0 h o u r s , l i q u i d h e l i u m l e v e l r e a c h e d t h e t o p o f t h e wind- Z-la i n g s . T o t a l l i q u i d h e l i u m consumption was 4~
2250 l i t r e s i n c l u d i n g t h e s u p p l i e s d u r i n g 1 8 h o u r s ' c h a r g i n g e x p e r i m e n t . S < -240
F i g i 5 shows a n example o f s t r a i n measurement r e s u l t s d u r i n g t h e c o o l down -"O
p r o c e s s . S t r a i n g u a g e s were a t t a c h e d on -320 0
t h e s u r f a c e s o f t h e o u t e r s t a i n l e s s
s t e e l s t r i p o u t s i d e o f t h e w i n d i n g s . Some ~i~
g u a g e s showed v e r y l a r g e s t r a i n s b u t most
o f t h e g u a g e s showed s t r a i n s w i t h i n 0.28. So some anoma- ( k A ) l o u s b e h a v i o u r may b e due t o u n e x p e c t e d i n i t i a l s t r a i n s d u r i n g t h e a t t a c h m e n t p r o c e s s o f g u a g e s . 10 -
2. CHARGING EXPERIMENT
F i g . 6 shows t h e s h o r t sample c r i t i c a l c u r r e n t c h a r - 8 - a c t e r i s t i c s and t h e l o a d l i n e s o f t h e magnet. T h e r e a r e two g r a d e s o f c o n d u c t o r s w i t h d i f f e r e n t c u r r e n t c a r r y i n g 6 - c a p a c i t i e s . Lower g r a d e c o n d u c t o r i s u s e d f o r a d o u b l e
pancake c o i l a t t h e upper end and f o r o n e a t t h e lower end a n d h i g h e r g r a d e c o n d u c t o r i s u s e d f o r o t h e r d o u b l e 4 - pancake c o i l s .
F i r s t , t h e magnet was c h a r g e d by a 4.5kA-YOV power s u p p l y . A f t e r some p r e p a r a t o r y o p e r a t i o n s below 100 amps,
peak c u r r e n t was g r a d u a l l y i n c r e a s e d , h o l d i n g t h e ramp L I I I ~ L I I I .
r a t e c o n s t a n t . ~t t h e f a s t e s t c h a r g e , t h e magnet was 2 4 6 8 B ( T ) c h a r g e d up t o 4430 amps i n 1 9 s e c o n d s . T h i s c o r r e s p o n d s Short and the load t o a f i e l d sweep r a t e o f 0.27 T/S and t h e maximum f i e l d l i n e o f the magnet
was 5.2 T. I n F i g . 7 , t h e c u r r e n t wave form and t h e t e r - ~~~~~:'=~~te&=~:~~
minal v o l t a g e o f t h e magnet a r e shown.
Then, we exchanged t h e power s u p p l y to, a 10kA-40V o n e . I n t h e same manner a s be- f o r e , peak c u r r e n t was g r a d u a l l y i n c r e a s e d and t h e magnet was c h a r g e d up t o 5520 amps i n a b o u t 8 0 s e c o n d s w i t h no t r a i n i n g . T h i s peak v a l u e i s 20 amps l a r g e r t h a n t h e de- s i g n e d v a l u e o f 5500 amps. A t t h i s t i m e , t h e s t o r e d e n e r g y r e a c h e d 4.0 M J and t h e maximum f i e l d was 6.4 T. F i g . 8 shows t h e c u r r e n t wave form and a n u n b a l a n c e d v o l t a g e o f a quench d e t e c t i n g c i r c u i t a t t h i s ope- r a t i o n . The c u r r e n t r e a c h e d 5000 amps i n 40 s e c o n d s a n d t h e n a ramp r a t e was slowed down and i t r e a c h e d 5520 amps i n a n o t h e r 40 s e c o n d s . The magnet was d i s c h r g e d a t o n c e i t r e a c h e d t h e p e a k . AS shown i n t h e
f i g u r e , i t was a q u i t e s t a b l e o p e r a t i o n . No motlon o f t h e c o n d u c t o r o r a d o u b l e pancake c o i l was o b s e r v e d a t a l l t h r o u g h t h e e x p e r i m e n t . No normal r e g i o n a p p e a r e d ,
e i t h e r .
F i g . 9 i s a t o p view o f a d o u b l e pan- c a k e c o i l and F i g . 1 0 i s a p h o t o g r a p h o f t h e magnet w i t h a c r y o s t a t . ( T h e s e two f i g -
= - = - 2 . 5 s ==--
' 4 4 3 0 W 1 9 5 z- - -
- ,-. - --- - -
Current v l v e torn and f
u r e s a r e on t h e bottom o f t h e n e x t p a g e . ) Pi'3.0 An o ~ u r o t i o ~ t Lo ttne denlgnrd of 5 5 0 0 ~
JOURNAL DE PHYSIQUE
ENERGY TRANSFER SYSTEM
Because of the limitation of the electric equipment of our labouratory, it is impossible for us to have a neccessary power supply for a pulsive operation of the magnet in about 1 second.Therefore, we decided to develop a power supply system using an energy transfer circuit. We have already con- structed an energy transfer circuit of 5 MW and an energy transfer experiment between the 4 MJ magnet
and a 400kJ-class magnet has been carried out in ,,g,ll
,,.,
gy eyntsmsuccess. Fig.11 illustrates the main circuit of the chopper circuits
system. This system consists of an energy storage
magnet, two chopper circuits, a capacitance for energy transfer and a test magnet.
A pulsed superconducting magnet with a stored energy of 3 MJ is under construction now using the same kind of conductor for the 4 MJ magnet. And an energy transfer experiment between MJ-class magnets will be carried out in march, 1984.
CONCLUSIONS
A pulsed superconducting cable of 5 kA-class at 6T with high purity aluminium as stabilizer was developed. Using this cable, we constructed a pulsed superconduct- ing magnet with a stored energy of 4 MJ. It consists of 12 double pancake coils.
The central field and the maximum field are 5.8 T and 6.4 T , respectively, at the operating current of 5500 amps. This magnet was successfully charged in dc operation to the designed value with no training. A pulsive operation of the magnet will be tried in an energy transfer experiment.
ACKNOWLEDGEMENT
The authors would like to express their gratitude to Dr.K.Sugiura and Dr.Y.Aiyama for their constant help and encouragement.
REFERENCES
l.T.Onishi,et.al.: Proc. of 8th Symp. on Engineering Problems of Fusion Research (San Francisco, USA, 1979)762
Z.T.Onishi,et.al.: Japanese Journal of Cryogenic Engineering,l6(1981)76 3.T.Onishi,et.al.: IEEE Trans. on Magnetics, Vol.MAG-17, No.5(1981)1958 4.H.Tateishi,et.a1.: Cryogenics,Vol.22, No.10(1982)509
5.T.Onishi,et.al.: Proc. of 9th Symp. on Engineering Problems of Fusion Research (Chicago, USA, 1981)1314
G.T.Onishi,et.al.: Proc. of ICEC-9,(Kobe,Japan,1982)446
Fig. 9
A top view of a double pancake coil Fig.10 A 4MJ-class pulsed magnet with a cryostat.
