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PULSED MAGNETS FOR THE TIME SHARING OF THE GANIL BEAM
A. Dael, M. Duval, Long Ao
To cite this version:
A. Dael, M. Duval, Long Ao. PULSED MAGNETS FOR THE TIME SHARING OF THE GANIL BEAM. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-293-C1-296. �10.1051/jphyscol:1984158�.
�jpa-00223714�
JOURNAL DE PHYSIQUE
Colloque C I , suppl6ment au no 1, Tome 45, janvier 1984 page Cl-293
PULSED MAGNETS FOR THE TIME SHARING OF THE GANIL BEAM
A. Dael, M. Duval and Long AO+
G A N I L , B.P. 5027, 14021 Caen Cedeac, F r a n c e
Resume - Le faisceau du GANIL peut d e s s e r v i r simultanement d i f f e r e n t e s experiences gr8ce .3 un systeme de partage de temps s u r 10 secondes.
Le champ d'un d i p o l e e s t monte e t s t a b i l i s e , en 500 m sec. , pour envoyer l e faisceau dans une premiere s a l l e de physique pendant 8 secondes. Puis l e champ de ce d i p o l e e s t descendu .3 nouveau en 500 m sec. e t l e faisceau se d i r i g e vers une a u t r e s a l l e de physique pendant une seconde.
Cepapier presente l a c o n c e p t i o n , l a technologie e t l e s mesures des 18 d i p o l e s pulses c o n s t r u i t s 2 c e t e f f e t .
A b s t r a c t -The beam o f t h e GANIL a c c e l e r a t o r complex can be used simultaneously by d i f f e r e n t experimental equipments through a time s h a r i n g system on 10 seconds.
The f i e l d o f a d i p o l e i s switched up i n 500 msec and t h e beam i s bent t o a p h y s i c i s t room f o r 8 seconds, then t h e f i e l d o f t h e d i p o l e i s switched down, again i n 500 msec, and t h e beam i s going s t r a i g h t on t o another p y s i c i s t f o r 1 second.
For t h a t purpose 18 pulsed magnets o f 5 tons have been b u i l t .
Design, c o n s t r u c t i o n , measurements and use of these magnets a r e presented, i n c l u d i n g t e c h n o l o g i c a l aspect.
Fig 1 : GANIL experimental areas Fig 2 : pulsed deviation
1. INTRODUCTION : TIME SHARING OF THE BEAM
V d d i p o l e s a r e used t o send t h e heavy i o n s beam t o t h e d i f f e r e n t expe- r i m e n t a l rooms.[l] E i g h t l i n e s are provided and a r e supplied through an e l e c t r i c a l commutation g r i d . The two d i p o l e s o f a l i n e a r e supplied s e r i a l and g i v e N a t o t a l d t - f l e x i o n o f 60 degrees t o t h e beam. See f i g u r e ( 1 ) and ( 2 ) t h e so c a l l e d f i s h bone o f t h e GANIL experimental areas. Two users can be served simultaneously, one being t h e main user, t h e " p i l o t " , t h e o t h e r being a secondary user, t h e " p a r a s i t " , who i s f o r instance t e s t i n g h i s experimental equipment. For t h a t purpose t h e d i p o l e which sends t h e beam t o t h e f i r s t concerned equipment i s pulsed according t o t h e f o l l o w i n g time c y c l e : see f i g u r e ( 3 )
The o v e r a l l time l e n g h t o f t h e c y c l e i s 10 seconds d i v i d e d i n :
- High f i e l d l e v e l B : d u r i n g 8 seconds t h e beam i s d e f l e c t e d t o t h e room
- zero f i e l d l e v e l : d u r i n g 1 second t h e beam goes s t r a i g h t on.
Twice 500 msec a r e l o s t f o r going up o r going down and t o g e t t h e f i e l d s t a b l e t o
lo-'+ These c h a r a c t e r i s t i c s l e a d t o a f i e l d v a r i a t i o n speed o f dB = Tesla,second a value which i s usual i n synchrotron magnets. d t
+visitor from Institute of Modern Physics Academia Sinica LANZHOU (the People's Republic of China).
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984158
JOURNAL DE PHYSIQUE
2. STATIC MAGNET DESIGN 2.1. General
The maanet i s p a r a l l e l . The main parameters a r e l i s t e d i n t a b l e 1. I t must work b e t - ween : - ~ m i n = 0,58 Tesla and ~ m a x ' = 2,5 x 0,58 Tesla = 1,44 Tesla. We have chosen an H magnet s t r u c t u r e both f o r magnetic and mechanical reasons.
2.2 Pgle-prgfi!e-gptim~s_a_t_i_g~
With t h e p o l e dimensions, t h e homogeneity i n a p a r a l l e l gap was o n l y * = 1.5
i n t h e u s e f u l area. B -
We have s t u d i e d a l a t e r a l shim o f 1 mm t h i c k t o improve t h i s homogeneity. The value of 1 mm i s chosen t o be o f t h e same order o f magnitude than t h e mesh s i z e o f t h e code models and a l s o punched.
The w i d t h o f t h e shim i s computed by successi- ' B
ve c a l c u l a t i o n s w i t h MAGNET and POISSON codes F i n a l l y w i t h our c a l c u l a t i o n model we f i n d a t
a f i e l d l e v e l B = 1.44 Tesla A B 4 1.0 i n II - 71
+ 63. mm w i t h POISSON, i n + 70. mm w i t h MAGNET I I I I I
I I I
The two computed curves a r e presented i n f i - I I I I
gure (6) compared w i t h t h e measured one which 1 I
gives&< 1.0 i n + 80. mm. !&
R 40 $e..nd* c p 1 c
2.3 ~t_u_i~-o_f_t_ie_-e_~i-er~f11~
We ask t o t h e end p r o f i l e the f o l l o w i n g pro- F i g 3 : time s h a r i n g c y c l e p e r t i e s :
(a) ?magnetic = emechanical
(b) a n t i s a t u r i n g shape t o keep t h e p r o p e r t y (a) and h i g h value o f t h e p e r m e a b i l i t y rt ( c ) p r o v i d e a magnetic l e n g h t adjustment t o g e t s e r i a l magnets as i d e n t i c a l as possi- b l e .
The e f f e c t o f a 9. mm t h i c k end shim, l o c a t e d as shown on f i g u r e (4), has been computed. We f i n d atmag = 2.88 niin so t h e e f f i c i e n c y i s 30 % and t h e end shim being made o f 6 sheets o f 1.5 mm, one can a d j u s t t h e magnetic l e n g h t o f one magnet w i t h a s e n s i v i t y o f 0.5 mm.
3. REMANENT FIELD COMPENSATION
The we I1 known formula B r = lli Hc ef gives
w i t h a good approximation e
B r = 20 G f o r Hc = 50A/m. To a v o i d t h e e f f e c t o f t h i s f i e l d on t h e "going on" beam, i t must be compensated. ,During t h e time s h a r i n g c y c l e t h e f i e l d i s c o r r e c t e d by a small negative c u r r e n t ( i r = - l.A) i n t h e main c o i l i t s e l f . For t h a t purpose t h e power supply i s designed t o d e l i v e r d i r e c t r e g u l a t e d c u r r e n t s from I = + 850 A t o i = - 15.A and t o work around t h e zero value. When t h e running c y c l e i s changed, t h e magnet undergoes a demagnetiza-
TABLE OF CHARACTERISTICS : Table-!
Characteristics
6;~T~;i&-~~gT; : eo = 30 degrees Curvature radius : R~ = 2.
Maximum f i e l d : B~~~ : 1-44 Tesla
Lenght : 1 = 1031. mm
Useful gap : e = 64. mm Coil characteristics
,;pp,-,-aimen;i;,-i;-> 11 mm mm
coil made of 2 double pancakes total number of twins : 48
~lectr~cal-cha_rgcte_[~s_t_i cs M a x i m u m i n t e n s i t y : 850. A
Resistance : 71.5 mn
Estimated inductance : 75 mH direct voltage : 64 v o l t s
: 191 v o l t s dt
Total voltage : 255 v o l t s power : 54 kW
Mechanical ---- --- characteristicS - - - I - - -
Dipole opening two y o ~ e s each yoke is made of 680 sheets of le5 mm thick.
of one di ole : 5, tons.
- t i o n c y c l e e i t h e r s h o r t ( I = Imax, I = - 0.1 Imax, I = 0) o r complete ( I = Imax, - 0,9 Imax
0,8 Imax, - 0,7 Imax ...)
4. EDDY CURRENTS PROBLEMS C
-
The end o f t h e magnets have been designed t o End p r o f i l e w i t h shim c' l i m i t t h e problems connected w i t h eddy currents
t o reduce t h e eddy c u r r e n t s o f aBz o r i g i n , t h e end p l a t e i s o n l y 12 mm at
t h i c k ( t i m e c o n s t a n t 7 = 100 msec). To l i m i t t h e eddy c u r r e n t s o f a B h o r i g i n we r e l y on t h e non s a t u r a t i n g a t
p r o f i l e which insures a h i g h rt value and on
t h e l i m i t a t i o n o f t h e end f l u x obtained by !mag = emecha. here a r e a l s o eddy c u r - r e n t s i n t h e s t a i n l e s s s t e e l vacuum chamber c r e a t i n g d i p o l e and sextupole perturba- t i o n s b u t o n l y d u r i n g t h e t r a n s i t i o n times, n o t d u r i n g t h e u s e f u l l e v e l s . So t h e r e i s no special inquirement on vacuum chamber except i n s u l a t i o n o f t h e f l a n g e s t o avoid c u r r e n t 1 oops.
5. TECHNOLOGY : STUCK END PLATES
The c o n s t r u c t i o n technology o f these d i p o l e s i s very c l a s s i c a l . We have used no b o l t and no t h i c k end p l a t e s . We have replaced t h e t h i c k end p l a t e by a composite o f one - p l a t e o f 12. mm and r o u g h l y 50 sheets o f 1.5 mm
a l l stuck together, making a composite end pla- t e o f 92. mm t h i c k . Such a composite j o i n s t h e mechanical q u a l i t i e s o f a s o l i d end p l a t e and t h e e l e c t r i c a l qua1 i t i e s o f i s o l a t e d sheets.
The sheets i n t h e middle o f t h e magnet a r e on- l y welded. The i n e r t i a o f t h i s composite p l a t e has been measured and i s considered as 50 % . t o 60 % o f t h e i n e r t i a o f a s o l i d p l a t e . The Rogwski p r o f i l e i s approximated by two chanfers i n t h e stuck p a r t . Precaution has been taken t o a v o i d s h o r t c i r c u i t between sheets.
6. MAGNETIC MEASUREMENTS 6.1. Ajm-gf-thg_mga_zu_rg!g!;~
Mainly, t h e measurements have t o r e s o l v e t h e problems o f t h e time sharing u t i l i z a t i o n : dy-
namic behaviour, remanent f i e l d , demagnetiza- Fig. : stuck end plates t i o n cycle. The magnets have been measured i n
s t a t i c w i t h H a l l probes and f l i p - f l o p c o i l s and i n dynamic w i t h i n t e g r a t i n g c o i l s . 6.2 Static_-njgazu_ygmytz
F i e l d maps a r e made i n t h e midplane, by mean o f a c a r r i a g e o f 21 H a l l probes, d r i v e n by step motors. The a l l system i s c o n t r o l l e d on l i n e by a M i t r a 125 computer, which manages t h e X Y displacement law and c a l c u l a t e s t h e B values. T h i s device has essen- t i a l l y f o r f u n c t i o n s :
- The measurement o f l o c a l f i e l d and r a d i a l homogenity : t h e f i g u r e (6) g i v e t h e r e - s u l t s compared w i t h MAGNET and POISSON c a l c u l a t i o n s .
- The measurement of magnetic l e n g t h and e f f i c i e n c y o f t h e end shims.
The magnetic l e n g t h i s c a l c u l a t e d on s t r a i g t h s x = c s t e . I f t h e d i f f e r e n c e on t h e two magnets i s worse than 10-3, we can a d j u s t t h e number o f t h e end shim sheets. The measured e f f i c i e n c y o f one sheet i s 0.43 mm.
I n p r a c t i c e t h e d i s p e r s i o n between magnet was l e s s than
- Determination o f f o c u s i n g wedges : t h e d i f - o P 60 10 10 X -
ference between t h e mechanical and magnetic angle i s 0.8'
6.3. Rgm~n_gn;-mga_s_u_rgm~n_t_~
We have measured t h e remanent f i e l d w i t h the
t u r n i n g l a r g e c o i l . We d e f i n e d t h e c u r r e n t I d , e - ~ ..
f o r t h e s h o r t demagnetization c y c l e and t h e small n e g a t i v e c u r r e n t ir used i n t h e time
sharing cycle. 4. P O ~ S S ~ ~
I. UM*NeT
6.4. E)yrgnc-mga_su_r~pnts 3- r ( t n l U ~ a
For t h a t purpose we have r e a l i z e d a system o f c o i l s . The main element i s a c o i l o f 65 turns, 1.6 meters long. I n s i d e t h i s c o i l , 9 s h o r t s c o i l s a r e placed. The voltages a r e i n t e g r a t e d w i t h a v o l t meter VIDAR 521C. The measurements
can be made : Fig 6 : radial homogeneity
- The magnet supplied w i t h d i r e c c u r r e n t : the
Cl-296 JOURNAL DE PHYSIQUE
c o i l s r o t a t e of 180' by pneumatic system. The integrator i s s t a r t e d and stopped res- pectively on 0 and 180% coil positon?
- The magnet supplied with pulsed current : the coil a r e fixed. The s t a r t of t h e integration i s given by the " s t a r t cycle" of the supply. The integration time can be chosen and incremented to plot the f i e l d versus time.(see figure 7 )
(b) coils inside the g a p ( c ) results
[Ll] : The G A N I L MAGNET SYSTEM presented by M. OHAYOPI these Proceeding MT8
