LARGE SCALE MAGNET SYSTEM FOR TANDEM MIRROR GAMMA 10

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LARGE SCALE MAGNET SYSTEM FOR TANDEM MIRROR GAMMA 10

S. Itoh, K. Yamamoto, K. Masuda, T. Sasaki, K. Inutake, I. Katanuma, K.

Yatsu, S. Miyoshi, Gamma 10 Group

To cite this version:

S. Itoh, K. Yamamoto, K. Masuda, T. Sasaki, K. Inutake, et al.. LARGE SCALE MAGNET SYSTEM

FOR TANDEM MIRROR GAMMA 10. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-189-

C1-192. �10.1051/jphyscol:1984139�. �jpa-00223694�

Colloque C l , supplbment au n o 1, Tome 45, janvier 1984 page Cl-189

L A R G E S C A L E MAGNET S Y S T E M F O R TANDEM M I R R O R GAMMA 11)

S. I t o h , K. Yamamoto, K . Masuda, T . Sasaki, K . l n u t a k e r , I. ~ a t a n u m a ~ , K. Yatsur, S. l l i y o s h i r and GAMMA 10 ~ r o u ~ + *

Toshiba Corporation, Yokohama, 230, Japan

'plasma Research Center, f i e U n i v e r s i t y of Tcukuba, 305, Japan

Rgsum6 - Cet a r t i c l e d E c r i t l e p l a n , l a f a b r i c a t i o n e t l e s r g s u l t a t s d ' e s s a i s du systsme d'aimant m i r r o i r en tandem GAMMA 10.

Le plan e t l a f a b r i c a t i o n soigneux a i n s i que Les a n a l y s e s p r E c i s e s s o n t e f f e c t u g s pour achever une d i s t r i b u t i - o n s o p h i s t i q u 4 e du champ magngtique avec une h a u t e p r g c i s i o n .

Les r E s u l t a t s d ' e s s a i s ont rEviilE que l e champ d ' e r r e u r e s t moins de 0,2%.

A b s t r a c t - This paper d e s c r i b e s d e s i g n , f a b r i c a t i o n and t e s t r e s u l t s of t h e magnet system f o r t h e tandem m i r r o r GAMMA 10. D e t a i l e d a n a l y s e s c a r e f u l design and

f a b r i c a t i o n were performed t o achieve s o p h i s t i c a t e d magnetic f i e l d d i s t r i b u t i o n w i t h high p r e c i s i o n .

Test r e s u l t s have r e v e a l e d t h a t e r r o r f i e l d i s l e s s t h a n 0.2%.

1 . I n t r o d u c t i o n

GAMMA 10, planned by Plasma Research Center, i s an axisymmetrized tandem m i r r o r f u s i o n experimental d e v i c e which i s provided w i t h axisymmetric thermal b a r r i e r s and end p l u g s i n o r d e r t o v e r i f y t h e o r e t i c a l background of t h e thermal b a r r i e r , and t o suppress t h e d i f f u s i o n l o s s i n r a d i a l d i r e c t i o n due t o t h e f i e l d asymmetry/l/.

The GAMMA 10 d e v i c e , manufactured by Toshiba Corporation, c o n s i s t s of vacuum v e s s e l , magnet system and a s s o c i a t e d support s t r u c t u r e s a s w e l l a s a d d i t i o n a l h e a t i n g

systems such a s n e u t r a l beam h e a t i n g and r a d i o frequency h e a t i n g S stems. The vacuum v e s s e l and t h e magnet system were completed i n March, 1982131, and t h e h e a t i n g systems were completed i n March, 1983. The overview of GAMMA 10 i s shown i n F i g . 1 . This device i s 27.1 m i n l e n g t h , and weighs 180 t o n . The GAMMA 10 d e v i c e i s expected t o c o n f i n e a plasma w i t h temperature of 1 keV and d e n s i t y of 1 ^X 1 0 l ~ c m - ~ . As shown i n F i g . 2, t h e magnet system c o n s i s t s of 6 meter-long s o l e n o i d magnet,

anchor and r e c i r c u l a r i z i n g c o i l s and axisymmetric p l u g l b a r r i e r c o i l s . Magnet a r - rangement was determined, t a k i n g account of s e v e r a l key f a c t o r s such a s r e c i r c u l a r -

+ M. ~ c h i m u r a , K. ~ s h i i , A. I t a k u r a , T . Kawabe, Y . Kiwamoto, A. Mase, T . S a i t o , K. Sawada, D . Tsubouchi, N . Yamaguchi

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984139

Cl-190 JOURNAL DE PHYSIQUE

7

I 2 4 6 8 10 12 14

Z-AXIS (m) (c)

Fig. 2 Base case of GAMMA 1 0 (mirror ratio of axisymmetric plug/mirror cell: R=6), (a) magnetic field distribution on axis, 0 is measured value, (b) plane view of magnetic lines of force and mod. B surface, (c) elevation view of

magnetic lines of force.

2 . Magnet design and magnetic field analysis

As for GAMMA 10 magnet design, it is necessary to determine coil shapes and arrangement, providing optimized field configuration, and to reduce the error fields to less than 0 . 2 % . Error field evaluation includes effects of several factors such as coil displacements due to electromagnetic forces, pancake to pancake transition conductors as well as feeders. In particular, the coil displacements due to the electromagnetic forces are key factors to design supporting structures, and it must be fully studied. Analytical result on a base case is shown in Fig. 2 .

Electromagnetic forces were evaluated for all operation patterns, Configuration of anchor and recircularizing coils is very complicated in particular, and is likely to get affected by electromagnetic forces. In the following electromagnetic forces acting on these coils and associated error field caused by coil displacement are analyzed.

2 . 1 Coil deformation and error field

The relative error field 6B is defined as 6B = ]BI] / ] B // I

On the machine center axis, B I = 0 because of symmetry, and hence, 6B = 0 . This means the error field will be generated by asymmetric coil deformation. Each coil is supported on the common base plate, and the electromagnetic force tends to deform the coil, deteriorating the coil symmetry. An error field caused by 1 mm upward coil deformation is 0 . 1 2 % at most.

2.2 Electromagnetic forces

For anchor and Recircularizing coils,the maximum excitation for all coils is

the most severe case from the standpoint of electromagnetic forces. Electro-

magnetic force distribution acting on the Anchor Baseball coil is shown in Fig. 3 .

On the Anchor Baseball coil, a widening force of 179 tons acts in X direction, and

on the race-track coil, a widening force of 3 0 5 . 6 tons acts in X direction. Since

the race-track coil is located in the open space of the Anchor Baseball coil, the

Electromagnetic f o r c e s a l s o a c t s i n p u l l i n g and r e p u l s i v e ways among c o i l s . The GAMMA 10 magnetic f i e l d system c o n s i s t s of f i v e m i r r o r f i e l d c o n f i g u r a t i o n s . P u l l i n g f o r c e s a t among c o i l s i n s i d e each m i r r o r r e g i o n , and a l s o among m i r r o r r e g i o n s . However, t h e former i s f a r g r e a t e r than t h e l a t t e r . Therefore, s u p p o r t i n g s t r u c t u r e f o r each c o i l block can be designed almost independently, and only t h e Anchor and Recir- c u l a r i z i n g c o i l s were modeled independently from t h e o t h e r s t o perform s t r u c t u r a l a n a l y s i s .

3 . S t r u c t u r a l a n a l y s i s 3.1 S t r u c t u r e

The s t r u c t u r e of t h e Min.-B and t r a n s i t i o n f i e l d c o i l system i s shown i n F i g . 4 . This system c o n s i s t s of t h e Anchor B a s e b a l l c o i l a t t h e c e n t e r , two r a c e - t r a c k c o i l s a t both s i d e s , and t h e main R e c i r c u l a r i z i n g c o i l s . In o r d e r t o keep t h e plasma volume i n t h e Min.-B f i e l d r e g i o n a s l a r g e a s p o s s i b l e , t h e Anchor B a s e b a l l c o i l s a r e wound d i r e c t l y around t h e vacuum v e s s e l . The r a c e - t r a c k c o i l s a r e i n s e r t e d i n t h e opening spaces of t h e Anchor Baseball c o i l , and e l e c t r o m a g n e t i c f o r c e s a c t i n g on t h i s c o i l i n X and Y d i r e c t i o n s a r e supported by t h e Anchor Baseball c o i l s , and t h e e l e c t r o m a g n e t i c f o r c e tending t o push t h e r a c e - t r a c k c o i l s o u t of t h e opening spaces i s supported by t h e R e c i r c u l a r i z i n g c o i l frame. The Anchor B a s e b a l l c o i l and two R e c i r c u l a r i z i n g c o i l s a r e independently f a s t e n e d on t h e common b a s e . The o v e r a l l magnet support s t r u c t u r e was designed i n such a way t o accommodate t h e above- mentioned e l e c t r o m a g n e t i c f o r c e s and a c c e s s i b i l i t y f o r t h e h e a t i n g and d i a g n o s t i c f a c i l i t i e s .

3.2 A n a l y t i c a l method and modeling

The c o i l s t r u c t u r e a n a l y s i s was c a r r i e d out with a q u a r t e r model shown i n F i g . 5 , u s i n g t h e NASTRAN t h r e e dimensional FEM code, and c o n s i d e r i n g symmetry of

t h e c o i l s t r u c t u r e and e l e c t r o m a g n e t i c f o r c e . For modeling t h e c o i l s t r u c t u r e , s o l i d elements were used, and t h e c r o s s - s e c t i o n s of t h e c o i l were d i v i d e d i n t o 9 (=3x3) s u b s e c t i o n s . Ground i n s u l a t i o n and t h e support s t r u c t u r e were modeled by s h e l l elements, s t u d b o l t s by b a r elements, and s p a c e r s between s u p p o r t s were modeled by s o l i d elements. Meshes of elements f o r t h e support s t r u c t u r e s a r e shown i n F i g . 5. T o t a l number of elements used f o r t h e s t r u c t u r a l a n a l y s i s was 2978.

3 . 3 R e s u l t s of c a l c u l a t i o n

C a l c u l a t i o n r e s u l t s have r e v e a l e d t h a t displacements of t h e Anchor and Recir- c u l a r i z i n g c o i l s a r e b o t h 0 . 5 m a t most i n X d i r e c t i o n , and t h a t mechanical s t r e s s e s appearing i n t h e s e c o i l s and t h e support s t r u c t u r e a r e below p e r m i s s i b l e v a l u e s f o r t h e m a t e r i a l s . The displacements of t h e Anchor B a s e b a l l c o i l and t h e a s s o c i a t e d s t r u c t u r e opening a r e almost uniform i n Y d i r e c t i o n , and t h i s deforma- t i o n i s mainly caused by e l o n g a t i o n of s t u d s and b o l t s which connect upper and lower p a r t s of t h e c o i l . I n o r d e r t o suppress t h e deformation, t h e s t u d s and t h e b o l t s were r e i n f o r c e d f o r t h e f i n a l design based on t h e c a l c u l a t i o n r e s u l t s . 4 . F a b r i c a t i o n of magnet

Two new method were adopted i n magnet f a b r i c a t i o n . One i s c u r r e n t pre-heating p r e s s u r e welding of t h e hollow conductor, which was developed t o improve t h e r e - l i a b i l i t y of t h e c o i l . The o t h e r was a newly developed two-axis winder t h a t was used f o r winding t h e b a s e b a l l c o i l . P a r t i c u l a r l y f o r t h e Anchor Baseball c o i l , t h e conductor was wound d i r e c t l y around t h e vacuum v e s s e l f2/. By t h i s method, t h e p r e c i s i o n i n i t s r e l a t i v e p o s i t i o n t o t h e vacuum v e s s e l was much improved, and a t t h e same time e f f e c t i v e plasma volume was g r e a t l y i n c r e a s e d .

I n c l u d i n g o t h e r c o i l s , much e f f o r t s were a l s o made t o keep t h e dimensional

e r r o r and alignment e r r o r below 0 . 5 mm, so t h a t t h e e r r o r f i e l d s a r e reduced t o

l e s s than 0.2%.

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5 . T e s t r e s u l t s

A f t e r completion of t h e whole system, v a r i o u s k i n d s of t e s t s were c a r r i e d o u t . Measurements of magnetic f i e l d d i s t r i b u t i o n and s t r u c t u r e d e f o r m a t i o n were c a r r i e d o u t d u r i n g f u l l c u r r e n t o p e r a t i o n . H a l l e l e m e n t s were used f o r f i e l d measurement, and t r a n s i t i n s t r u m e n t s and s t r a i n gauges were used f o r d e f o r m a t i o n measurement.

The magnetic f i e l d measurement r e s u l t a l o n g t h e machine a x i s i s shown i n F i g . 2 ( a ) , and measured time v a r i a t i o n of t h e f i e l d a t Z = 3.7 m, i s shown i n F i g . 6 . The f a b r i c a t i o n and a l i g n m e n t e r r o r of t h e magnet system was l e s s t h a n 0.5 mm. The measurements by t r a n s i t i n s t r u m e n t s show t h e d i s p l a c e m e n t s of t h e s t r u c t u r e t o b e l e s s t h a n 0 . 5 mm.

6 . Conclusions

D e t a i l e d a n a l y s e s on magnetic f i e l d , e l e c t r o m a g n e t i c f o r c e s and mechanical s t r e s s were c a r r i e d o u t p r i o r t o t h e d e s i g n and t h e f a b r i c a t i o n of t h e GAMMA 10 d e v i c e . Comparison between measured and c a l c u l a t e d v a l u e s of magnetic f i e l d s and d i s p l a c e r n e n t s showed good agreements.

About f o u r thousand s h o t s of o p e r a t i o n was c a r r e i d o u t u n t i l August, 1983. GAMMA 10 i s now under o p e r a t i o n a s a tandem m i r r o r equipped w i t h f o u r s e t s of n e u t r a l - b e a m - i n j e c t i o n system.

R e f e r e n c e s

(1) Tandem M i r r o r GAMMA 10 and i t s c o n t r i b u t i o n t o r e a c t o r d e s i g n , p r o c . T h i r d IAEA T e c h n i c a l Committee Meeting and Workshop on F u s i o n R e a c t o r Design a n d Technology, 5-16 O c t . , 1982, Tokyo, Japan, 1A~~-TC-392/25, v o l . I, p.429, VIENNA, 1983.

( 2 ) K. I n u t a k e e t a l . , Design, f a b r i c a t i o n and t e s t i n g of tandem m i r r o r GAMMA 10, P r e s e n t e d 1 2 t h Symp. on F u s i o n Technology, J u l i c h , S e p t . 1982.

F i g . 3. E l e c t r o m a g n e t i c f o r c e d i s t r i b u t i o n a c t i n g on t h e Anchor B a s e b a l l c o i l

Crms s e c l a A - A

F i g . 4 . S t r u c t u r e of t h e a n c h o r a n d r e c i r c u l a r i z i n g c o i l s

Stud B o l t '

F i g . 6 . Time v a r i a t i o n of magnetic F i g . 5 . Meshes of e l e m e n t s f o r t h e s u p p o r t s t r u c t u r e f i e l d at t h e c e n t e r of t h e

r e c i r c u l a r i z i n g c o i l (Z=3.7m)