INSULATION SYSTEMS ENGINEERING

(1)

HAL Id: jpa-00223595

https://hal.archives-ouvertes.fr/jpa-00223595

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 published 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.

INSULATION SYSTEMS ENGINEERING

Hanna Becker, P. Marston

To cite this version:

Hanna Becker, P. Marston. INSULATION SYSTEMS ENGINEERING. Journal de Physique Collo- ques, 1984, 45 (C1), pp.C1-615-C1-617. �10.1051/jphyscol:19841125�. �jpa-00223595�

(2)

JOURNAL DE PHYSIQUE

Colloque C1, supplCment au no 1, Tome 45, janvier 1984 page C1-615

I,NSULATION SYSTEMS ENGINEERING

H. Becker and P.G. Marston

PZasrna Fusion Center, Massachusetts I n s t i t u t e o f TeehnoZogy, Cambridge, MA 02139, U.S.A.

RQsumd - En 6 t a n t a t t e n t i f 2 c e r t a i n s d g t a i l s d e c o n s t r u c t i o n il e s t p o s s i b l e de t i r e r p a r t i d e l a g r a n d e r d s i s t a n c e d e s i s o l a n t s o r g a n i q u e s pour c o n c e v o i r d e s systSmes d ' i s o l a t i o n d ' a i m a n t s d e f u s i o n p l u s e f f i c a c e s . En a m d l i o r a n t l a c o n c e p t i o n d e s i s o l a t e u r s d ' a i m a n t s p a r l ' u t i l i s a t i o n d e s p r o p r i 6 t G s m6ca- n i q u e s de f e u i l l e s minces il d e v i e n d r a p o s s i b l e d e l e s f a i r e f o n c t i o n n e r 2 d e s n i v e a u x de rayonnement c o r r e s p o n d a n t 2 d e s f l u e n c e s p l u s d l e v g e s , a v e c comme b d n d f i c e 6conomique une t a i l l e e t un coQt r G d u i t s .

A b s t r a c t - With c a r e f u l a t t e n t i o n t o e n g i n e e r i n g d e t a i l d e s i g n , i t i s p o s s i b l e t o t a k e advantage of h i g h s t r e n g t h o r g a n i c i n s u l a t o r s t o d e s i g n more e f f i c i e n t f u s i o n magnet i n s u l a t i o n s y s t e m s . By o p t i m i z i n g i n s u l a t o r / magnet d e s i g n t h r o u g h maximum u s e of t h i n s h e e t mechanical p r o p e r t i e s , i t may a l s o b e p o s s i b l e t o o p e r a t e a t a h i g h e r r a d i a t i o n f l u e n c e l e v e l w i t h a d d i t i o n a l economic payoff i n reduced magnet s i z e and c o s t .

INSULATION SYSTEMS ENGINEERING

I n s u l a t i o n systems e n g i n e e r i n g , a s a p p l i e d t o s u p e r c o n d u c t i n g magnet s y s t e m s , r e - l a t e s t h e d e s i g n i n t e g r a t i o n of t h e c o n d u c t o r , e l e c t r i c a l i n s u l a t i o n , s u p p o r t s t r u c t u r e and c o o l i n g r e q u i r e m e n t s of t h e c o i l winding t o t h e m a t e r i a l s p r o p e r t i e s t e s t i n g and development programs f o r t h e e l e c t r i c a l i n s u l a t i o n . The e f f o r t t h u s emphasizes t h e r o l e of t h e i n s u l a t o r a s a s t r u c t u r a l element of t h e magnet system and i d e n t i f i e s t e s t a r r a n g e m e n t s which s i m u l a t e t h e l o a d i n g c o n d i t i o n s f o r d i f f e r e n t winding d e s i g n c o n f i g u r a t i o n s .

The t e c h n i q u e i s p a r t i c u l a r l y u s e f u l f o r a s s e s s i n g g l a s s r e i n f o r c e d p l a s t i c ( g r p ) l a m i n a t e s f o r which m e c h a n i c a l p r o p e r t i e s a r e s e v e r e l y a n i s o t r o p i c and f o r which s u r v i v a b i l i t y a s a n i n s u l a t o r i n t h e r a d i a t i o n environment of a f u s i o n r e a c t o r i s t h e r e f o r e s e v e r e l y d e s i g n dependent.

A s a s i m p l e example, t h e p r e l i m i n a r y work completed t o d a t e h a s shown t h a t e x i s t i n g polyimide/SZ g l a s s l a m i n a t e s , i f l o a d e d p r i m a r i l y i n compression p e r p e n d i c u l a r t o t h e l a y e r s of c l o t h ( w i t h l i t t l e o r no i n t e r l a m i n a r s h e a r ) , a r e s u i t a b l e f o r toka- mak t o r o i d a l and p o l o i d a l windings. Design c o n f i g u r a t i o n s embodying t h a t p r i n c i p l e a r e b e i n g e x p l o r e d and a p p e a r t o be a c h i e v a b l e .

Two p o t e n t i a l a d v a n t a g e s t o b e g a i n e d from l o n g e r - l i v e d , s t r o n g e r o r g a n i c i n s u l a - t o r s a r e reduced system s i z e and c o s t , s t i m u l a t e d by a reduced o u t e r r a d i u s of t h e s h i e l d i n g , o r i n c r e a s e d plasma minor r a d i u s and r e l a t e d power i n c r e a s e i f t h e s h i e l d i n g i n n e r r a d i u s can b e i n c r e a s e d .

Another g a i n c a n b e a c h i e v e d i n t h e g r e a t e r f l e x i b i l i t y i n p r o d u c t s i z e of o r g a n i c s compared t o i n o r g a n i c s . Organics c a n b e produced i n l a r g e s h e e t s o r long s t r i p s and may o n l y have t o b e l a i d i n p l a c e w h i l e ceramic t i l e s may r e q u i r e c o n n e c t i n g o r

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841125

(3)

C1-616 JOURNAL DE PHYSIQUE

cementing, b o t h of which would i m p a r t low r e l i a b i l i t y t o t h e i n s u l a t i o n system.

O r g a n i c s c a n f o l l o w s h a p e d e v i a t i o n s and s t r u c t u r a l d e f o r m a t i o n s w i t h o u t f a i l u r e whereas i n o r g a n i c s are less f l e x i b l e . Emplaced o r g a n i c s would n o t b e s u b j e c t t o

c r a c k i n g and e r o s i o n which c o u l d o c c u r i n ceramic c o a t i n g s t h a t u s u a l l y a r e a p p l i e d i n t h i c k n e s s e s of t h e o r d e r of 0.05 t o 0 . 1 m.

SURVIVABILITY REQUIREMENTS

-

I n s u l a t i o n i n a f u s i o n r e a c t o r magnet system must s u r v i v e 50 c y c l e s (maximum) of 275 MPa normal p r e s s u r e , 1 5 v o l t s between c o n d u c t o r s , 500 v o l t s p e r m i l breakdown, 1018 n/cm2 and 2 x l o 6 Gy ( 1 Gy, o r Gray, = 1 j o u l e p e r k i l o g r a m ) of gamma r a d i - a t i o n .

The n e u t r o n f l u e n c e i s a n i n t e g r a t e d v a l u e o v e r a wide r a n g e of e n e r g i e s from n e a r t h e r m a l (< O.1MeV) t o a s h i g h a s 1 4 MeV.

S u r v i v a l d a t a on s e v e r a l o r g a n i c c o m p o s i t e s i n a gamma r a d i a t i o n environment a r e p r e s e n t e d i n F i g u r e 1 from / I / .

It was h y p o t h e s i z e d and shown e x p e r i m e n t a l l y t h a t t h i n s h e e t o r g a n i c l a m i n a t e s would s u r v i v e b e t t e r under f a c e compression t h a n r o d s loaded p a r a l l e l t o l a m i n a t e p l a n e s . / 2 / Subsequent t e s t s / 3 / d e m o n s t r a t e d t h a t t h e f a c e p r e s s u r e s t a t i c s t r e n g t h of u n i r r a d i a t e d l a m i n a t e s i s s e n s i t i v e t o sample t h i c k n e s s w i t h a t r a n s - i t i o n v a l u e of a b o u t 1 mm. At t h i c k n e s s e s between 1 mm and 6 mm, a p l a t e a u v a l u e of f a c e p r e s s u r e s t a t i c s t r e n g t h of + 600 MPa was observed. For t h i c k n e s s e s between 0 . 5 mm and l m m , t h e s t r e n g t h was observed t o r i s e s t e e p l y t o v a l u e s con- s i d e r a b l y above t h o s e f o r t h e t h i c k e r s e c t i o n s . T e s t s a r e i n p r o g r e s s t o d e f i n e s t r e n g t h i n t h i s t h i c k n e s s regime.

Specimens were i r r a d i a t e d t o 3 x l o 9 Gy gammas p l u s 3 x l o z 0 n/cm2, which i s a l m o s t two o r d e r s of magnitude g r e a t e r t h a n t h e specimens of F i g u r e 1 l o a d e d p a r a l l e l t o laminas. The h i g h l y dosed d i s k s were loaded t o 250,000 c y c l e s a t 640 MPa f a c e p r e s s u r e w i t h no s i g n o f f a i l u r e . They a l s o s u r v i v e d 2,750 MPa s t a t i c a l l y / 3 / . Furthermore, t h e n / y d i s t r i b u t i o n of f l u e n c e i n t h e e x p e r i m e n t s was 1 1 3 which a p p r o a c h e s t h e r a n g e e x p e c t e d i n a f u s i o n r e a c t o r magnet. The specimens of F i g u r e 1 r e c e i v e d n e a r l y p u r e gamma i r r a d i a t i o n . It a l s o i s i m p o r t a n t t o i n d i c a t e t h a t t h e polyimide/SZ g l a s s specimens were n o t observed t o e x h i b i t d e l a m i n a t i o n a f t e r warmup from 4 K nor was s i g n i f i c a n t s t r e n g t h l o s s e n c o u n t e r e d / 4 / .

A t p r e s e n t i t would a p p e a r t h a t PS2 s h e e t i s a prime c a n d i d a t e f o r f u s i o n magnet i n s u l a t i o n i f a winding pack c o n f i g u r a t i o n can b e developed t h a t would c o n f i n e t h e i n s u l a t i o n l o a d i n g t o normal f a c e compression t h e r e b y a v o i d i n g o t h e r problems s u c h a s i n t e r l a m i n a r s h e a r (ILS) s t r e n g t h . I f ILS cannot b e a v o i d e d c o m p l e t e l y , i t s t i l l may n o t be a problem b e c a u s e t h e r e s u l t s of t h e t e s t s on u n i r r a d i a t e d lami- n a t e s s u g g e s t t h a t h i g h f a c e p r e s s u r e can i n c r e a s e ILS s t r e n g t h . T h i s remains t o b e e s t a b l i s h e d .

I f t h e d e s i g n p r e s s u r e i s 250 MPa and a s a f e t y f a c t o r of 3 i s assumed, t h e n t h e s t a t i c l o a d s t r e n g t h would have t o b e 750 MPa. That would b e l e s s t h a n 30 p e r c e n t of t h e above mentioned v a l u e o f 2,750 MPa a f t e r a t o t a l e q u i v a l e n t e n e r g y absorp- t i o n o f 4 x l o 9 Gy (gammas p l u s n e u t r o n s ) . No d a t a e x i s t a t p r e s e n t f o r e x t r a p o - l a t i n g t h a t i n f o r m a t i o n t o s t r e n g t h s a t h i g h e r f l u e n c e s . It may b e r e a s o n a b l e t o a n t i c i p a t e a comparable s t r e n g t h l e v e l a t 1 0 l 0 Gy. It a l s o i s c o n c e i v a b l e t h a t a l a r g e f r a c t i o n of t h a t s t r e n g t h c o u l d b e a c h i e v e d a t 1011 G b u t t e s t s a r e r e q u i r e d t o e s t a b l i s h t h a t f i g u r e . I f PS2 c a n s u r v i v e 750 MPa a t 10'' Gy, i t would h a v e a p r a c t i c a l a d v a n t a g e o v e r i n o r g a n i c s b e c a u s e of t h e i n h e r e n t l y g r e a t e r s t r u c t u r a l f l e x i b i l i t y and t h e a v a i l a b i l i t y i n t h i n s h e e t form. A program i s now underway t o d e t e r m i n e t h e p , o s s i b i l i t y of a c h i e v i n g t h a t r e s u l t by d o u b l i n g t h e d o s e on some specimens and q u a d r u p l i n g t h e d o s e on o t h e r s t o r e a c h 8 x l o 9 Gy and 1 . 6 x 1 0 l 0 Gy, r e s p e c t i v e l y . Those r e s u l t s may p e r m i t e x t r a p o l a t i o n of s t r e n g t h d a t a t o h i g h e r d o s e l e v e l s .

(4)

A l l s t r u c t u r a l t e s t i n g t o d a t e h a s been conducted a f t e r removal of specimens from t h e r a d i a n t s o u r c e . An i n p i l e l o a d i n g program i s now underway t o e v a l u a t e t h e e f f e c t on i n s u l a t o r s t r e n g t h . T e s t s a l s o a r e b e i n g o r g a n i z e d t o i n c r e a s e t h e dose l e v e l on ps2 t o v a l u e s a p p r o a c h i n g 101° e q u i v a l e n t Gy f o r c y c l i c and s t a t i c s t r e n g t h t e s t s .

The U.S. DOE program on i n s u l a t o r s r e q u i r e s e s t a b l i s h m e n t of i n s u l a t o r d e s i g n d a t a by FY188. It i n c l u d e s g e n e r a t i o n of r e l i a b l e m e c h a n i c a l and e l e c t r i c a l p r o p e r t y d a t a , s t a n d a r d i z a t i o n o f m a t e r i a l p r o p e r t y d a t a and t e s t methods, v e r i f i c a t i o n t e s t i n g of magnet components i n a r a d i a t i v e environment and p r o c e d u r e s f o r c r e a t i n g development of sound system e n g i n e e r e d c o n f i g u r a t i o n s . Most of t h e p r o g r e s s t o d a t e h a s been made on t h e f i r s t two i t e m s .

NORPLEX ,I

, '

.---_----

0 -

0 0 . 5 ~

lo8 lo8

G a m m a Radiation Dose, G y Q 0

ZI

In tn

& 2 500

v w

- .-

a n

a

F i g . 1 S t a t i c Compressive S t r e n g t h s of Organic Composites A f t e r I r r a d i a t i o n .

REFERENCES

.

-

1. R. R. Coltman, J r . , "Organic I n s u l a t o r s and t h e Copper S t a b i l i z e r f o r Fusion R e a c t o r Magnets," J o u r n a l of Nuclear M a t e r i a l s , 108 and 109, 1982., pp 559-571.

II Laminas Porallel t o Rod Axis

I L a m i n a s Perpendicular t o Rod Axis

.-.. _\

.

^\₁

\ 1 _\

.

^,SPAULRAD\ ^II

2. E. A . Erez and H. Becker, " R a d i a t i o n Damage i n Thin S h e e t F i b r e g l a s s I n s u l a - t o r s , " Nonmetallic M a t e r i a l s and Composites a t Low Temperature

-

^2. (Hartwig and Evans, E d s ) , Plenum P r e s s , 1982, pp 59-71.

Curves ore A v e r a g e s of S c a t t e r Bands

G - 10 CR II

3 . H. Becker, et a l . , MIT Plasma F u s i o n C e n t e r Report i n P u b l i c a t i o n . 4. C. E. Klabunde and R. R. Coltman, J r . , "Debonding of Epoxy from G l a s s i n

I r r a d i a t e d Laminates," Symposium on R a d i a t i o n Damage A n a l y s i s f o r F u s i o n R e a c t o r s , S t . , L o u i s , October 24-28, 1982.