THE ASDEX UPGRADE POLOIDAL FIELD COILS

HAL Id: jpa-00223690

https://hal.archives-ouvertes.fr/jpa-00223690

Submitted on 1 Jan 1984

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

THE ASDEX UPGRADE POLOIDAL FIELD COILS

M. Pillsticker, Félix Werner

To cite this version:

M. Pillsticker, Félix Werner. THE ASDEX UPGRADE POLOIDAL FIELD COILS. Journal de

Physique Colloques, 1984, 45 (C1), pp.C1-171-C1-176. �10.1051/jphyscol:1984135�. �jpa-00223690�

THE ASDEX UPGRADE POLOIDAL FIELD COILS

M. Pillsticker and F. Werner

Mm-PZanck-Institut fiir PZasmaphysik, EURATOM Association, 0-8046 Garching, F. R. G.

Ce papier d6crit le systsme de bobines du champ pololdal de 11exp6rience ASDEX Upgrade de Garching.

Abstract

This paper describes the poloidal field coil system of the Garching divertor experiment ASDEX Upgrade.

Introduction

ASDEX Upgrade is a plasma experiment of the tokamak type that is now under construction. Its aim is ko study the divertor principle for plasma impurity control in

reactor-relevant arrangement. "Reactor-relevant" in this sense means, that all poloidal field (PF) coils, the divertor or vertical

field coils and the ohmic heating

transformer coils are situated outside the toroidal field

magnet (Fig.

Fig.

ASDEX Upgrade, disposition of PF coils

In contrast to the existing axisymmetric divertor machines, where the divertor coils are positioned relatively close to the plasma, this arrangement requires enlarged divertor coils with circulation currents in the

range.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984135

JOURNAL DE PHYSIQUE

The OH t r a n s f o r m e r produces a maximum magnetic f l u x of 4 . 7 5 V s c o u p l e d w i t h t h e plasma. The t o t a l f l u x swing of 9 . 5 V s a l l o w s t h e plasma, which behaves l i k e a t r a n s f o r m e r secondary winding, t o be b u i l t up, h e a t e d , and m a i n t a i n e d f o r s e v e r a l seconds.

The maximum c u r r e n t induced i n t h e plasma i s 2 MA.

The V c o i l system i s d e s i g n e d t o produce two d i f f e r e n t d i v e r t o r f i e l d d i s t r i b u t i o n s , t h e s o - c a l l e d d o u b l e n u l l ( D N ) and s i n g l e n u l l (SN) c o n f i g u r a t i o n s .

I / M A

B a s i c F e a t u r s ^@/VS

A l l PF c o i l s a r e m u l t i - winding c i r c u l a r c o i l s wound from water-cooled copper c o n d u c t o r s . Each winding l a y e r r e p r e s e n t s a c o o l i n g c i r c u i t w i t h w a t e r i n l e t and o u t l e t . Thermal s t r e s s e s a r e m i - nimized by homogeneous c o o l i n g and f r e e t h e r m a l expansion wherever pos- s i b l e . The t e m p e r a t u r e i s l i m i t e d t o a maximum p e r - m i s s i b l e v a l u e of T = 353 K . During e x c i t a t i o n and de- e l e c t r i c a l l y s t r e s s e d by t h e i n d u c t i v e v o l t a g e e x c i t a t i o n t h e c o i l s a r e drop. A l l c o i l s a r e over- ¹ v o l t a g e - p r o t e c t e d , f a u l t 0

c o n d i t i o n s and e x c e s s i v e c u r r e n t s a r e a v o i d e d by a m o n i t o r i n g and s a f e t y c o n t r o l

t e r i s t i c system. time-dependent Charac- - 2

- : D o

OH f l u x and V _{c o i l}

c u r r e n t s a r e g i v e n i n 1

" I ^I l I

F i g . 2 . Some c h a r a c t e r i s 0 I

t i c d a t a a r e g i v e n i n - 5. ' v ~ ( I c ~

T a b l e 1 .

For more d e t a i l s s e e / l / . ^{- l T} ' v ~ ( " c I

F i g . 2 : PF magnetic f l u x and c u r r e n t c h a r a c t e r i s t i c f o r S N o p e r a t i o n . The OH System

The OH system c o n s i s t s of t h e c e n t r a l t r a n s f o r m e r c o i l OH 1 and t h e c o i l p a i r s OH 2 and OH 3. A l l 5 OH c o i l s a r e c o n n e c t e d i n s e r i e s . The f l u x swing of 9 . 5 V s i s predominantly produced by t h e c o i l OH 1 , whereas t h e c o i l s OH 2 and OH 3 s e r v e t o r e d u c e t h e magnetic f l u x d e n s i t y i n t h e plasma r e g i o n t o a v a l u e of l e s s t h a n 0.003 T i n c a s e of maximum OH e x c i t a t i o n ( F i g . 3 ) .

Table 1: C h a r a c t e r i s t i c c o i l d a t a .

Z F i g . 3 : OH f i e l d d i s t r i b u t i o n .

The e l e c t r i c a l s t r e s s of t h e OH system depends on t h e m a x i - mum d i / d t of t h e OH c u r r e n t n e c e s s a r y t o i n d u c e a s u f f i - c i e n t l y h i g h plasma v o l t a g e Vp t o c a u s e plasma breakdown.

Of s p e c i a l i n t e r e s t was t h e e v a l u a t i o n of t h e i n f l u e n c e of t h e vacuum v e s s e l , a c t i n g a s a t r a n s f o r m e r secondary winding, on t h e breakdown v o l t a g e . Corresponding network c a l c u - l a t i o n s were done w i t h t h e a i d of t h e ECAP network a n a l y s i s programme. From e x p e r i e n c e w i t h t h e ASDEX e x p e r i m e n t , a

. .

plasma l o o p v o l t a g e of 50 V i s assumed t o be s u f f i c i e n t . To r e a c h t h i s v a l u e , t h e c h a r g e d OH system h a s t o be d i s c h a r g e d w i t h a t i m e c o n s t a n t of 100 m s . The i n d u c t i v e v o l t a g e d r o p a t t h e OH c o i l s r i s e s up t o 30 kV, a v a l u e t h e i n s u l a t i o n a g a i n s t ground h a s t o w i t h s t a n d .

F i g u r e 4a shows t h e dependence of t h e OH v o l t a g e and t h e plasma l o o p v o l t a g e v e r s u s d i s c h a r g e r e s i s t a n c e . The vacuum v e s s e l r e - s i s t a n c e p a r a m e t e r i s 0.25 mOhm. The i n f l u e n c e of t h e v e s s e l r e - s i s t a n c e on t h e plasma l o o p v o l t a g e i s g i v e n i n F i g . 4b.

The d i s c h a r g e r e s i s t a n c e p a r a m e t e r i s 0.6 Ohm, which i s e q u i v a - l e n t t o a d i s c h a r g e t i m e c o n s t a n t of 100 m s .

JOURNAL

DE

P i g . 4: a ) OH c o i l v o l t a g e VOH and plasma l o o p v o l t a g e Vpl v s . D i s c h a r g e r e s i s t a n c e ROH

b ) Plasma l o o p v o l t a g e Vpl v s . vacuum v e s s e l r e s i s t a n c e RV.

The OH 1 c o i l i s s o l e n o i d w i t h a l e n g t h of 3 m , a major d i a m e t e r of 1.02 m , and a minor d i a m e t e r of 0.51 m. The r a t i o of t h e d i a - meter chosen ( d ( m i n ) /d(max) = 0.5) i s a good compromise between t h e mechanical and t h e t h e r m a l l o a d s and l e a d s t o n e g l i g i b l e r a d i a l s t r e s s e s . S i n c e f i n a l l y t h e mechanical s t r e s s i s t h e l i m i - t i n g f a c t o r , a symmetric f l u x swing ( 5 4.75Vs) i s r e q u i r e d .

The c o i l OH 1 i s h e l i c a l l y wound and c o n s i s t s of 10 c y l i n d r i c a l l a y e r s w i t h 51 t u r n s each. For c o n d u c t o r m a t e r i a l SE Cu F 2 5 was s e l e c t e d . The c y l i n d r i c a l l a y e r s a r e i n t e r n a l l y connected i n s e r i e s a t t h e i r bottom and t o p ends.

The s i n g l e c o n d u c t o r s and t h e whole c o i l a r e i n s u l a t e d w i t h f i b r e g l a s s - r e i n f o r c e d epoxy r e s i n c o n t a i n i n g c a s t - i n polyimide f o i l s f o r improved e l e c t r i c breakdown s t r e n g t h . The t h i c k n e s s of t h e c o n d u c t o r i n s u l a t i o n i s 2.5 mm. The c o i l i n s u l a t i o n i s c o v e r e d w i t h a c o n d u c t i n g g r a p h i t e l a y e r t o a v o i d s u r f a c e breakdown.

Each winding c y l i n d e r h a s i t s own c o o l i n g c i r c u i t such t h a t i n - l e t s and o u t l e t s a r e a r r a n g e d a t t h e t o p and bottom f r o n t ends of t h e c o i l .

The l i m i t e d l e n g t h of t h e c o n d u c t o r s makes i t n e c e s s a r y t o b r a z e them. I n o r d e r t o r e s t o r e t h e o r i g i n a l s t r e n g t h , t h e b r a z e d s e c t - i o n s w i l l be cold-worked by s t r e t c h i n g .

The c o o l i n g c h a n n e l c r o s s - s e c t i o n s and w a t e r p r e s s u r e ( p = 2 0 b a r ) a r e determined by a cooling-down t i m e of 10 min. I n o r d e r t o en- s u r e homogeneous t e m p e r a t u r e s d u r i n g c o o l i n g , t h e w a t e r f l o w i s reduced w i t h b a f f l e s f o r t h e i n n e r winding c y l i n d e r s , which c a r r y

t h e r m a l s t r e s s e s which a c t i n t h e same d i r e c t i o n . Mechanical and t h e r m a l s t r e s s e s a c t v e r t i c a l l y i n o p p o s i t e d i r e c t i o n s . E l a s t i c b e a r i n g s a t t h e c o i l f r o n t e n d s t a k e up t h e 5 mm v e r t i c a l l e n g t h v a r i a t i o n and a l s o a l l o w f r e e r a d i a l expansion.

The r e q u i r e m e n t s imposed on t h e OH 1 c o i l a p p l y e s s e n t i a l l y t o t h e OH 2 c o i l a s w e l l , b u t t o a reduced e x t e n t . S p a t i a l con- s t r a i n t s r e q u i r e t h i s c o i l t o be wound on r a d i a l d i s c s . I t con- s i s t s of 9 pancakes of 9 t u r n s e a c h , e a c h pancake having i t s own c o o l i n g c i r c u i t . The c o o l i n g w a t e r f l o w s from t h e o u t e r t u r n of e a c h pancake t o t h e i n n e r one. The c o o l i n g c h a n n e l s a r e of e q u a l l e n g t h and e v e n l y d i s t r i b u t e d , s o t h a t t h e r m a l s t r e s s i n g of t h e i n s u l a t i o n i s minimized.

The OH 3 c o i l i s t o be wound a s o n e - l a y e r d i s c . I t i s r e i n f o r c e d by mounting it t o t h e V 2 m u l t i p o l e c o i l i n a way which a l l o w s h o r i z o n t a l s l i d i n g between them.

The V e r t i c a l F i e l d C o i l s

I n dimensioning t h e V c o i l s , symmetric and unsymmetric l o a d con- d i t i o n s had t o be c o n s i d e r e d . The upper and lower c o i l s of e a c h t y p e a r e s e p a r a t e l y o p e r a t e d i n s e r i e s . I n c a s e of t h e unsymmetric S N o p e r a t i o n o n l y p a r t s of t h e upper V 1 and V 2 , and t h e lower V 3 a r e used. A l l c o i l s a r e a r r a n g e d a s c l o s e l y a s p o s s i b l e t o t h e t o r u s s t r u c t u r e . T h a t i s why t h e c o i l s V 2 a r e wound i n a rhomboidal c r o s s - s e c t i o n .

The c o i l c o n c e p t i s based on s i m p l e and s t a n d a r d t e c h n i q u e s . A l l c o i l s a r e composed of r a d i a l l y wound pancakes c o n n e c t e d a t

t h e i r o u t e r and i n n e r c i r c u m f e r e n c e . S E Cu F 2 5 a g a i n was s e l e c t e d a s m a t e r i a l . The i n s u l a t i o n c o n s i s t s o f f i b r e - g l a s s - r e i n f o r c e d epoxy r e s i n . Only a t t h e c o n n e c t i o n s a d d i t i o n a l i n s u l a t i o n i s r e q u i r e d i n t h e form of polyimid f o i l s . The w a t e r c o o l i n g i s p r o v i d e d i n t h e pancake l a y e r s w i t h i n l e t s and o u t l e t s a t t h e o u t e r and i n n e r c i r c u m f e r e n c e .

Loads and S t r e s s e s of PF c o i l s

Thermal s t r e s s e s a r e reduced t o t h e i r minimum v a l u e s by a l l o w i n g f r e e expansion wherever p o s s i b l e . The r e t a r d e d t e m p e r a t u r e r i s e of t h e i n s u l a t i o n compared w i t h t h e c o n d u c t o r produces s t r e s s e s w i t h i n t h e i n s u l a t i o n . However, s i n c e t h e t h e r m a l expansion i s a s m a l l f r a c t i o n of t h e expansion and s t r a i n produced by t h e I X B f o r c e s , t h e r m a l s t r e s s e s have been t a k e n i n t o a c c o u n t by s u f f i c i e n t l y e n l a r g i n g t h e s a f e t y margin.

The I X B f o r c e s a c t i n g i n t h e r a d i a l and v e r t i c a l d i r e c t i o n s a r e b a l a n c e d r a d i a l l y by hoop s t r e s s e s and v e r t i c a l l y by a s u p p o r t s t r u c t u r e . S i x t e e n s u p p o r t s r e s t i n g on t h e c i r c u m f e r e n c e r e d u c e bending s t r e s s e s t o

<

JOURNAL DE PHYSIQUE

The d i f f e r e n t l o a d c o n d i t i o n s and t h e d i r e c t i o n of v e r t i c a l f o r c e s ( u p o r down) depend on t h e c o n f i g u r a t i o n (SN, D N ) , t h e OH c o i l e x c i t a t i o n l e v e l and s i g n . F i g u r e 5 shows t h e v e r t i c a l l o a d i n t i m e F z ( t ) i n t r o d u c e d by each c o i l f o r t h e SN mode of o p e r a t i o n .

A l l s t r e s s e s of t h e V c o i l s were a n a l y - t i c a l l y c a l c u l a t e d . T h i s was j u s t i f i e d by t h e s a t i s f a c t o r y comparison of FE c a l c u l a t i o n s w i t h a n a l y t i c a l c a l c u l a - t i o n s of t h e OH 1 c o i l s t r e s s i n g , t h i s b e i n g t h e c o i l w i t h t h e most c r i t i c a l

s t r e s s d i s t r i b u t i o n . The maximum con- d u c t o r s t r e s s e s i n t h e c e n t e r of t h e OH 1 c o i l a r e c a l c u l a t e d t o amount t o 130 MPa. The s h e a r s t r e s s i s l e s s t h a n 1.5 MPa.

I n o r d e r t o f e e d t h e OH c o i l s , magnetic f i e l d s of up t o 6 T have t o b e c r o s s e d w i t h c o n d u c t o r s c a r r y i n g c u r r e n t s of a b o u t 50 kA. A s t h e p o l o i d a l f i e l d t o be c r o s s e d h a s no component i n t h e t o - r o i d a l d i r e c t i o n and t h e c u r r e n t s i n t h e l e a d - i n s f l o w i n e i t h e r t h e r a d i a l o r t h e v e r t i c a l d i r e c t i o n , o n l y f o r c e s i n t h e t o r o i d a l d i r e c t i o n a r e produced.

The maximum l i n e l o a d a c t i n g on t h e s i n g l e c o n d u c t o r s of t h e l e a d - i n s i s 0.3 Mp/m.

Ref e r e n c e

/ l / ASDEX Upgrade P r o j e c t P r o p o s a l , Phase 2 , W. Koppendorfer e t a l . , IPP 1/217, May 1983.

g tls

-.4 - v 2 (uc)

: b_ _ _ _ _ _ _ _ _ _ _ _ _ l v t l s

Fig..: V e r t i c a l l o a d F z . ( t ) f o r SN o p e r a t i o n .

-." v3(lc) V3(uc)

---with plasma