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HIGH RAMP RATE SUPERCONDUCTING PULSED MAGNETS
T. Ogasawara
To cite this version:
T. Ogasawara. HIGH RAMP RATE SUPERCONDUCTING PULSED MAGNETS. Journal de
Physique Colloques, 1984, 45 (C1), pp.C1-443-C1-449. �10.1051/jphyscol:1984191�. �jpa-00223747�
HIGH RAMP RATE SUPERCONDUCTING PULSED MAGNETS
T. Ogasawara
College o f Science and Technology, Nihon U n i v e r s i t y , Kanda Surugadai, Chiyoda-ku, Tckyo 101, Japan
Resume - Le developpement de bobines poloTdales s u p r a c o ~ d u c t r i c e s e s t examine. Par l ' e t u d e des problemes techniques e t l ' a p p r e c i a t i o n du p r o - gres accompli, on e s t amen@ & c o n c l u r e q u ' u n t r e s grand e f f o r t s e r a n e c e s s a i r e pour r e a l i s e r des tokamaks de t a i l l e s a u s s i b i e n moyenne que grande.
A b s t r a c t - A s u r v e y o f s u p e r c o n d u c t i n g p o l o i d a l c o i l development f o r tokamaks i s presented. E v a l u a t i o n o f p r o g r e s s and i n v e s t i g a t i o n o f t e c h n i c a l i s s u e s l e a d t o t h e c o n c l u s i o n t h a t much e f f o r t i s needed f o r t h e r e a l i z a t i o n o f b o t h medium and l a r g e - s c a l e tokamaks.
Superconducting magnets o p e r a t e d i n t h e d.c. mode have g a i n e d w i d e acceptance i n t h e i r a p p l i c a t i o n s i n v a r i o u s f i e l d s d u r i n g t h e p a s t two decades. However, t h e R & D o f superconducting p u l s e d magnets have been r a t h e r modest e x c e p t f o r h i g h energy p h y s i c s r e s e a r c h and t h i s i s e s p e c i a l l y t r u e f o r " h i g h ramp r a t e p u l s e d magnets".
These p u l s e magnets a r e t o be used m a i n l y i n t h e tokamak machine, which i s t h e p r i m a r y concern o f t h i s paper.
The p o l o i d a l f i e l d (PF) c o i l system i n tokamaks i s r e q u i r e d t o p r o v i d e t h e f u n c t i o n s o f i n i t i a t i o n , h e a t i n g , shaping and e q u i l i b r i u m o f t h e plasma. I n l a r g e - s c a l e tokamaks such as P!ET, ETR, FER and IMTOR, one o f t h e o b j e c t i v e s i s t o demonstrate t h e f e a s i b i l i t y o f t h e tokamak as a power g e n e r a t i n g machine. I n o r d e r t o r e a l i z e t h e break even o f energy, t h e superconducting TF and PF c o i l s y s t e m s ' a r e needed. The maximum p u l s i n g r a t e o f PF c o i l s i s about 10T/s a c c o r d i n 9 t o t h e conceptual d e s i g n s t u d i e s . T h i s s i t u a t i o n i s d i f f e r e n t f o r medium s i z e d e x p e r i m e n t a l tokamaks: The i n c e n t i v e f o r u s i n g s u p e r c o n d u c t i n g PF c o i l s i s weak as l o n g as t h e plasma con- f i n e m e n t t i m e i s s h o r t . I n a l o n g p u l s e o p e r a t i o n , >30 seconds, however, t h e super- c o n d u c t i n g v e r s i o n i s u s e f u l f r o m t h e v i e w p o i n t o f e l e c t r i c power s a v i n g . R e c e n t l y r e s e a r c h programmes o f such a l o n g p u l s e tokamak a r e a t t r a c t i n g an i n c r e a s i n g i n t e r e s t i n t h e f u s i o n community. The p u l s e r a t e o f PF c o i l s i n t h e medium s i z e tokamak i s as h i g h as 100T/s and t h e t e c h n o l o g i c a l f e a s i b i l i t y has n o t been e s t a b l i s h e d y e t . I n t h e f o l l o w i n g s e c t i o n s , t h e p r e s e n t s t a t u s o f t h e development o f superconducting p u l s e d magnets a r e d e s c r i b e d and t h e n 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 a r e i d e n t i f i e d .
I - PULSED MAGNETS DEVELOPED OR UNDER DEVELCPMENT
Table 1 PF c o i l s o f t h e n e x t gener- The u l t i m a t e t a r g e t o f t h e R & D i s t h e
r e a l i z a t i o n o f s u p e r c o n d u c t i n q PF c o i 1 s a t i o n tokamak (example o f FER / I / ) o f t h e n e x t g e n e r a t i o n tokamak. The c o i l s i z e 3-20m 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 r e - number o f c o i 1 s 12-22 q u i r e d c h a r a c t e r i s t i c s as shown i n Table maximum c u r r e n t 30-100kA 1 / I / . T h i s t a b l e a l s o i n d i c a t e s t h e f i e l d ramp r a t e 10T/s f o l l o w i n g t e c h n o l o g i c a l problems: s t o r e d energy 5-8GJ
- development o f heavy c u r r e n t c o n d u c t o r s a.c. l o s s / s t o r e d energy < 0.2%
w i t h a c a p a c i t y up t o lOOkA number o f p u l s e s 4 x 105
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984191
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- h i g h ramp r a t e o f t h e f i e l d
- t h e r e q u i r e m e n t o f l o w a.c. l o s s e s ; t h e l o s s t i m e c o n s t a n t must be l e s s t h a n lms
- mechanical r e q u i r e m e n t s ; f a t i g u e toughness a g a i n s t 4 x 105 c y c l i c o p e r a t i o n s Next we proceed t o t h e d e s c r i p t i o n o f t h e developmental e f f o r t s on s u p e r c o n d u c t i n g p u l s e magnets i n t h e w o r l d . T a b l e 2 l i s t s t h e summary o f t h e r e s u l t s .
USA The US development programme o f s u p e r c o n d u c t i n g p u l s e mapnets f o r f u s i o n s i v e s f r o m t h e p i o n e e r i n g work c e n t e r e d a t Los Alamos K a t i o n a l Laboratory(LGNL).
The o b j e c t i v e was t o develop h i p h l y e f f i c i e n t , p u l s e d , s u p e r c o n d u c t i n g m a y e t i c energy s t o r a g e (SblES) system f o r t h e Theta P i n c h concept. S e v e r a l p u l s e magnets were de- ,veloped. A 300kJ c o i l was c h a r ~ e d u p t o 13.4kA and d i s c h a r o e d t o z e r o i n 2.4ms a t a maximum d i s c h a r g e v o l t a g e o f 58kV/2/. A 400kJ c o i l was d i s c h a r g e d i n 1.07ms and a l s o conducted f i e l d r e v e r s a l t e s t s i n a few seconds/3/. These t y p e s o f energy s t o r a g e and t r a n s f e r systems w i l l have d e r i v a t i v e a p p l i c a t i o n s i n v a r i o u s f u s i o n machines.
A f t e r t h e c o m p l e t i o n o f t h e s e works, t h e p r o j e c t o f t h e PF c o i l system was s t a r t e d t o c o n s t r u c t and t e s t a 50kA, 20MJ c o i l t h a t would demonstrate t h e t e c h n o l o g i c a l f e a s i - b i l i t y o f a tokamak ohmic h e a t i n g coi1/4,5/. The c o i l was t o be designed and con- s t r u c t e d b y Westinghouse E l e c t r i c Corp.(W) on c o n t r a c t t o LANL. A l t h o u o h LAKL had completed t h e t e s t f a c i l i t y , t h e p r o j e c t has been postponed i n d e f i n i t e l y .
A t Argonne N a t i o n a l L a b o r a t o r y (ANL), t h e f i r s t I l J - c l a s s c o i l has been developed and e x t e n s i v e l y tested/6,7,8/. The c o i l was charped t o 4.4T i n 0.4s and d i s c h a r g e d t o zero i n 0.6s a c h i e v i n g a maximum ramp r a t e o f 11T/s. A f t e r more t h a n 4000 p u l s e t e s t s 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 as w e l l as t h e c r y o s t a b i - l i t y . Another s i n n i f i c a n t p r o g r e s s a t A!!L i s t h e development o f t h e Pulsed Cable Test F a c i l i t y (PCTF)/9,10,11/. The p a r a v e t e r s o f t h e PCTF s p l i t - p a i r c o i l i s com- pared w i t h t h e 1.5b1J c o i l i n Table 3. The purpose o f t h e PCTF i s t w o f o l d : F i r s t l y , i t can be used t o t e s t developmental h i g h c u r r e n t c o n d u c t o r s under p u l s i n g f i e l d s i n a f o r m o f pancake c o i l s o r as a s h o r t sample f o r t h e s t u d i e s o f a.c. l o s s e s , s t a b i l i t y and c o o l i n g channel design. Secondly, t h e p u l s e o p e r a t i o n o f t h e PCTF c o i l i t s e l f i s a t e s t o f l l k A c a b l e and t h e c o i l s t r u c t u r e . The c o i l was c h a r o e d , t o 10.6kA i n 1.0s Table 2 Superconducting p u l s e c o i l s developed o r under development. E s - s t o r e d energy, Bm-maximum f i e l d , I o - o p e r a t i o n c u r r e n t , J o - c u r r e n t d e n s i t y , d B / d t - f i e l d ramp r a t e
I n s t i t u t e Es(F1J) Bm(T) I o ( k A ) Jo(A/cmz) d B / d t ( T / s ) c o n d u c t o r LANL/W
LAPIL/W ANL ANL, PCTF ETL, MK-3 ETL , MK-4 ETL, MK-5 JAERI, Pulser-C JAERI , Pulser-D JAERI , Pul ser-E
IPPJ, RPC-I IPPJ, RPC-I1 Osaka Univ.
Toshiba LANL/W JAERI
NbTi/Cu F!bTi/Cu/CuNi KbTi/Cu/solder MbTi/Cu/solder NbTi/Cu/CuNi NbTi/Cu/CuNi NbTi /Cu/CuNi/Al
NbTi/€u/CuNi NbTi/Cu/Cuh'i NbTi/Cu/CuNi NbTi/Cu/CuNi NbTi/Cu/CuNi NbTi/Cu/CuNi NbTi/Cu/CuKi NbTi/Cu/CuNi NbTi/Cu/CuNi Notes - i t e m dB/dt: D-discharge mode, U-charge u p mode
- i t e m Es: * - w i t h t h e backup f i e l d c o i l , Pulser-C
- 20115 c o i l s a r e i n t h e d e s i g n s t a g e
800 p u l s e s w i t h r e p e t i t i o n p e r i o d s o f 10-15 seconds, no changes o f t h e c o i l charac- t e r i s t i c s have been observed. F i g u r e 1 shows t h e PCTF c o i l i n an assembly stage.
S h o r t l y a t e s t o f a 25kA-class p u l s e d c o n d u c t o r i s scheduled t o be done. ANL i s a l s o p l a n n i n ~ s t u d i e s o f energy s t o r a g e and t r a n s f e r u s i n g t h e PCTF and t h e 1.5'iJ c o i l .
Table 3 Parameters o f two ANL c o i l s parameters
peak f i e l d a t I l k A ( T ) i n n e r d i a m e t e r (cm) o u t e r d i a m e t e r (cm) a x i a l l e n g t h (cm) number o f t u r n s c a b l e dimensions (cm) c a b l e l e n g t h (m) i n d u c t a n c e (mH) Cu/NbTi r a t i o
c o n d u c t o r volume (m3) c o i l c u r r e n t d e n s i t y (A/cm2) l a y e r t o l a y e r s p a c i n g (cm) a.c. l o s s e s a t 9T/s (kV)
1.5MJ c o i l 4.5 41.6 81 .O 58.1 258 3.78x0.74
510 24 18.6 67x10-3
2685 0.32-0.48
2.65
3.3145 c o i l 6.5 45.1 87.2 62.2 + gap
402 3.05x0.63
84 0 55
JAPAN The R & D o f tokamk PF c o i l s has been i n i t i a t e d a t t h e E l e c t r o t e c h n i c a l L a b o r a t o r y
(ETL). Two 400kJ c o i l s has been developed and t e s t e d /12,13/, c f . Table 2: MK-3 and MK-4 a r e wound from a compacted c a b l e and a b r a i d e d cable, r e s p e c t i v e l y . Since t h e o v e r a l l c u r r e n t d e n s i t i e s a r e q u i t e h i g h , t h e s e c o i l s have been o p e r a t e d a t c u r r e n t l e v e l s c o n s i d e r - a b l y l a r g e r t h a n t h e r e c o v e r y c u r r e n t . As a n e x t step, a 4MJ c o i l has r e c e n t l y been con- s t r u c t e d , Table 4/14,15/. S p e c i a l f e a t u r e t o be n o t e d i s t h a t h i g h - p u r i t y aluminum has been used as t h e s t a b i l i z e r . F i g u r e 2 shows t h e c a b l e c o n s t r u c t i o n . T h i s c a b l e can meet t h e c o n f l i c t i n g r e q u i r e m e n t s o f h i g h s t a b i l i t y and l o w a.c. l o s s e s : The observed r e c o v e r y c u r r e n t o f t h e f i n a l c a b l e was about 6kA, whereas t h e d e s i g n o p e r a t i o n c u r r e n t was 5.5kA.
The l o s s t i m e c o n s t a n t o f t h e c a b l e was measured t o be 1.4111s. The e s t i m a t e d t o t a l l o s s o f t h e c o i l f o r m 6T b i p o l a r swing i n 2
seconds i s about 0.1% o f t h e s t o r e d energy. F i g . 1 - Assembly o f t h e AEL PCTF The d e t a i l s a r e t o be r e p o r t e d i n t h i s
c o n f e r e n c e / l 5 / . The ETL i s now c o n s t r u c t i n g a n o t h e r 3MJ c o i l as a matching c o i l t o t h e 4b2J c o i l f o r t h e s t u d i e s o f t h e c o i l performance and energy s t o r a g e / t r a n s f e r between t h e two c o i l s .
The Japan Atomic Energy Research I n s t i t u t e (JAERI) i s r e s p o n s i b l e f o r t h e c o n s t r u c -
t i o n o f t h e FER, t h e n e x t tokamak a f t e r JT-60. F o r FER p o l o i d a l c o i l s , JAEKI i s
d e v e l o p i n g h i g h - c u r r e n t p u l s e d c o n d u c t o r s and p u l s e d c o i l s f o r t e s t i n g t h e c o n d u c t o r s
/16-19/. Table 5 shows t h e o v e r a l l p l a n f o r t h e development o f a 20MJ p u l s e c o i l .
Two 10kA c o n d u c t o r s , JA-10 and JB-10, were s e l e c t e d as an i n t e r m e d i a t e s t e p t o 50kA
conductors, JA-50 and 36-50. The c o n s t r u c t i o n s o f JA-10 and 38-10 a r e v e r y s i m i l a r
t o t h o s e o f JA-50 and 36-50, r e s p e c t i v e l y , c f . F i g s . 3 and 4 . M a j o r d i f f e r e n c e i s
t h e d e s i g n p r i n c i p l e f o r g e t t i n g h i g h s t a b i l i t y . I n JA-10, an e f f i c i e n t c o o l i n g i s
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Table 4 Parameters o f ETL 4MJ c o i l
number o f double pancakes 12
maximum f i e l d a t 5.53kA ( T ) 6.4 i n n e r d i a m e t e r (cm) 50.0 o u t e r d i a m e t e r (cm) 95.8
a x i a l l e n g t h (cm) 63.0
number o f t u r n s 792
c a b l e dimensions (cm) 2.0x0.54
c a b l e l e n g t h (m) 1810
i n d u c t a n c e (mH) 260
o p e r a t i o n c u r r e n t (kA) 5.53 c o i l c u r r e n t d e n s i t y (A/cm2) 3040
c o i l w e i g h t ( k g ) 1800
Table 5 JAERI development work f o r PF c o i l s Conductor
Development
Large Current
Large Energy
(10150. 2 5 T l s ) (8~011 torus. 100T/sJ
( a ) JA-50
( p o o l - c o o l e d , 50kA, 7T)
( b ) JB-50
( p o o l - c o o l e d , 50kA, 7T)
( c ) JF-30 ( f o r c e d -
c o o l ed ,
30kA, 7T)
F i g . 3 - Cross s e c t i o n s o f 30 - 50kA p u l s e d conductors developed by JAERI, c f . F i g . 4
Cu NbTi
-CuNi- Clad Strand
99.999 %
A l --
1st Sub-cable
Kapton ,
( 5 0 ~ )
CuNt - 2nd Sub-cable
SUS 304
i
E
E
Final Cable
D LD
f
F i ? . 2 - Cable c o n s t r u c t i o n o f A l - s t a b i 1 i z e d c o n d u c t o r f o r t h e ETL 4MJ c o i l
- - -
3 5 Subcables
7.5
,567 strands
Strand
Filament
F i g . 4 - C o n s t r u c t i o n o f JAERI 30-50kA
p u l s e d c o n d u c t o r s
c o i l s , Pulser-D and Pulser-E were wound f r o m JA-10 and JB-10, r e s p e c t i v e l y , and t e s t - ed i n a background p u l s e d c o i l c a l l e d Pulser-C, c f . Table 2. The c o m b i n a t i o n o f Pulser-C & D generated 6.7T f i e l d and s a f e l y d i s c h a r g e d a t a r a t e o f 13T/s. The c o m b i n a t i o n Pulser-C & E was t e s t e d under t h e c o n d i t i o n o f 5.8T and 16T/s. F u r t h e r p r o g r e s s a t JAERI i s t h e development o f h i g h c u r r e n t c o n d u c t o r s . I n Table 5, JA-50 and 58-50 a r e two 50kA, p o o l - c o o l e d c o n d u c t o r s and JF-30 i s a 30kA, f o r c e d c o o l e d c a b l e - i n - c o n d u i t conductor, F i g s . 3 and 4. Each c o n d u c t o r has i t s u n i q u e f e a t u r e : h i g h s t a b i l i t y b y e f f i c i e n t c o o l i n g (JA-501, h i o h s t a b i l i t y b y r e c h a n i c a l r i g i d i t y (JB-50), and h i g h v o l t a g e i n s u l a t i o n and s t r u c t u r a l s t r e n g t h ( J F - 3 0 ) . The f a b r i c a - b i l i t y o f t h e s e c o n d u c t o r s was proven b y s h o r t samples.
The R e a c t i n g Plasma P r o j e c t o f t h e I n s t i t u t e o f Plasma P h y s i c s ( I P P ) , Nagoya U n i v e r - s i t y , i s d e v e l o p i n g a medium s i z e , D-T b u r n i n g tokamak/20/. Design 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 c o i l s w i t h a maximum p u l s i n g r a t e o f about 100T/s.
I f t o t a l l y s u p e r c o n d u c t i n g o p t i o n o f t h i s tokamak i s chosen, one o f t h e k e y t e c h - n o l o g i e s t o be developed i s t h e superconducting PF c o i l s . Based on t h e p r o o f o f t h e s c i e n t i f i c f e a s i b i l i t y / 2 1 / , t h e j o i n t team o f IPP, Nihon U n i v e r s i t y , M i t s u b i s h i E l e c t r i c Corp. and ETL has been engaged i n t h e R & D o f p u l s e m g n e t s / 2 2 - 2 5 / . I n t h e d e s i g n p r i n c i p l e o f a c a b l e d c o n d u c t o r , an emphasis was g i v e n on l o w a.c. l o s s e s and t h e r e f o r e a t h i n b a s i c s t r a n d w i t h mixed m a t r i x was chosen. The c a b l e c o n s t r u c t i o n i s shown i n F i g . 5. The f i n a l c a b l e ( 2 . 3 3 ~ 1 ~ x 0.41cm) has a c u r r e n t c a r r y i n g c a p a c i - t y o f lOkA a t 6T and t h e l o s s t i m e c o n s t a n t o f 0.3ms. Two model c o i l s , RPC-I and RPC-11, were wound f r o m t h e above c o n d u c t o r , c f . Table 2 . The p u l s i n g t e s t o f t h e s e c o i l s were performed by a condenser d i s c h a r g e method w i t h a clamp c i r c u i t . I n t h e RPC-I, t h e p u l s e r a t e o f 150T/s was o b t a i n e d i n t h e charge-up p e r i o d b y a p p l y i n g a t e r m i n a l v o l t a g e o f 7.0kV. The a.c. l o s s was about 0.5% o f t h e energy s t o r e d i n t h e c o i l . A t a h i g h e r v o l t a g e a breakdown o f i n s u l a t i o n o c c u r r e d and t h e second c o i l , RPC-11, has been c o n s t r u c t e d w i t h r e i n f o r c e d i n s u l a t i o n . The t e s t r e s u l t s a r e g i v e n i n F i g . 6 and Table 2. l,lore d e t a i l s a r e p r e s e n t e d i n t h i s conference/25/.
EUROPE The development programme on t h e PF c o i l system f o r b o t h medium s i z e and -scale tbkamaks w i l l be s t a r t e d by t h e end o f 1983/26/. The o u t l i n e o f t h e
programme has been j o i n t l y prepared by KfK/Fermany and CEA/France. The f i r s t and medium t e r m t a r g e t i s t o b u i l d an e q u i l i b r i u m r i n p c o i l f o r Tore Supra/27/ o r Asdex- upgrade. T h i s c o i l w i l l b e t e s t e d under t h e o p e r a t i n g c o n d i t i o n o f tokamaks by r e - p l a c i n g one o f normal c o n d u c t i n g c o i l s . Developmental e f f o r t s t o approach t h i s t a r g e t are;-Development o f Tow l o s s FlbTi c o n d u c t o r w i t h l o s s t i m e c o n s t a n t s between O.lms and lms f o r p u l s i n g r a t e s up t o 200T/s. - S t u d i e s on optimum c o o l i n g modes.
-Mechanical d e s i g n s t u d i e s and t e s t i n g of n o n - m e t a l l i c m a t e r i a l s . -Developnlent and F i n a l
Cable
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