THE GANIL MAGNET SYSTEM

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THE GANIL MAGNET SYSTEM

M. Barré, D. Bibet, M. Bourgarel, A. Chabert, A. Dael, M. Duval, J. Fermé, C. Eveillard, J. Libin, M. Ohayon, et al.

To cite this version:

M. Barré, D. Bibet, M. Bourgarel, A. Chabert, A. Dael, et al.. THE GANIL MAGNET SYSTEM.

Journal de Physique Colloques, 1984, 45 (C1), pp.C1-195-C1-205. �10.1051/jphyscol:1984140�. �jpa- 00223695�

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JOURNAL DE PHYSIQUE

Colloque Cl, suppl6ment au n o 1, Tome 45, janvier 1984 _pageCl-195

T H E G A N I L M A G N E T S Y S T E M +

M. Barrb, D. B i b e t , M.P. Bourgarel, A . Chabert, A . Dael, M. Duval, J . Ferm6, C. E v e i l l a r d , J.F. L i b i n , M. Ohayon and J. S a u r e t

GANIL : B. P. 5027, 14021 Caen Cedex, France

Resume - Le GANIL (Grand Accslerateur National d11ons Lourds) se compose de q u a t r e X E Z E r a t e u r s , deux i n j e c t e u r s (CO1 e t COe), deux grands acc6lerateurs ( a secteurs

s&par@s CSSlet CSS2). Cet ensemble comprend aussi b i e n quatre l i g n e s de f a i s c e a u pour l a machine e t l e s a i r e s experimentales, que des aimants speciaux pour l e s phy- s i c i e n s . GANIL a commence a f o n c t i o n n e r en novembre 1982 e t l e s experiences de physique o n t d@but@ en j a n v i e r 1983.

A b s t r a c t - The GANIL (Grand Accel6rateur National d l I o n s Lourds) c o n s i s t s o f f o u r accelerators, two i n j e c t o r c y c l o t r o n s (CO1 and CO2), two b i g a c c e l e r a t o r s (separated s e c t o r c y c l o t r o n s SSCland SSC2). T h i s complex i n c l u d e s as w e l l as f o u r beam l i n e s f o r the machine and t h e experimental areas, and s p e c i a l magnets f o r p h y s i c i s t s . The GANIL running s t a r t e d i n november and t h e f i r s t p h y s i c s e x p e r i m e n t took p l a c e i n january 1983.

1 - THE GANIL MACHINE

The GANIL machine supported by t h e two french i n s t i t u t i o n s C.E.A. and I.N.2.P.3. (Atomic Energy Commission and National I n s t i t u t e o f Nuclear Physics and P a r t i c l e Physics) i s now b u i l t i n CAEN (Calvados). The c o n s t r u c t i o n of t h e GANIL l a b o r a t o r y on t h e s i t e of CAEN was decided and funded i n September 1975. The GANIL scheme has been described i n previous p u b l i c a - t i o n s ( 1 ) ; l e t us however r e c a l l t h e main

- a c c e l e r a t i o n o f a l l i o n species from carbon t o uranium w i t h a maximum energy o f about 100 MeV/A for l i g h t ions and 10 MeV/A f o r t h e heaviest : beam i n t e n s i t i e s i n the order of 1012 t o 10' pps, energy r e s o l u t i o n !$! = 10-3.

Tn order t o f u l f i l these beam condivions an a c c e l e r a t o r complex was chosen which i s composed

l a r g e c y c l o t r o n s , a per f o i l provides high- e r charge s t a t e s (op

+ p r e s e n t e d by M. Ohayon

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984140

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Cl-196 JOURNAL DE PHYSIQUE

t h e h i g h energy beam coming from SSC2 passes through a monochromator and then e n t e r s t h e experimental area ( F i g . 1).

This monochromator i s used f o r t u n i n g the two SSC and a l s o t o ensure i n any case t h e d e l i v e r y u n t o t h e experimental area o f a beam w i t h good energy spectrum : i n c r e a s i n g the energy r e s o l u t i o n t o + 2.5.10-'+.

2 - INJECTOR CYCLOTRON

T h i s i n j e c t o r i s a f l a t p o l e t i p c y c l o t r o n ( H type magnet) w i t h an edge shimming ( F i g . 2) and a s e t of 6 p a i r s of c i r c u l a r c o i l s t h a t i s a b l e t o c o r r e c t the f i e l d g r a d i e n t t o o b t a i n t h e t h e o r i t i c a l f i e l d and v e r t i c a l f o c u s i n g ( F i g . 3) i n the 0.6 -

1.9 T f i e l d range ( 2 ) .

The t r i m - c o i l s are made o f a 7 X 6 mm conductor w i t h a 4 mm diameter hole. They are placed i n s i d e a vacuum t i g h t box, 1 . 5 mm t h i c k . Braces between adjacent c o i l s , brazed l e d ( b r a z i n g w i t h f i l l i n g weld) and epoxy vacuum f i l l i n g provide t h e r e q u i r e d s t i f n e s s .

The shimming i s machined t o r e c e i v e t h e vacuum l e a d o f t h e vacuum chamber ; t h a t alows t o minimise t h e c o i l t o c o i l d i s t a n c e and t o o b t a i n a good e f f i c i e n c y (70 %) a t 1.9 T and t o reduce t h e f r i n g e f i e l d .

F I E L D & G R A D I E N T

3 - MAIN CYCLOTRONS (SSC)

3.1 - Fleld-~onf~suratlon-of-th_~~s~c1otron-s

Each c y c l o t r o n has f o u r separated s e c t o r s o f 52 degrees. The gap i s 100 mm. The magnet must keep i t s p r o p e r t i e s i n t h e range o f 0.65 T t o 1.65 T and t h e average magnetic f i e l d along t h e l o c a l isochronous o r b i c must be p r o p o r t i o n a l t o t h e r i g h t y value i n t h e u s e f u l area d e f i n e d by i n j e c t i o n and e x t r a c t i o n e q u i v a l e n t r a d i i .

(Ri = 857.2 mm ; R, = 3 200 mm). Beyond these values the p o l e t i p s have been extended 2.7 and 3 gap-lengths, r e s p e c t i v e l y ( 3 ) .

The F i g u r e 4 shows the i s o m e t r i c view o f one o f t h e Ganil separated sectors c y c l o - trons, w i t h t h e f o u r s e c t o r s and t h e vacuum chamber.

The F i g u r e 5 g i v e s a schematic mid plane of the magnetic elements o f an SSC i n c l u - d i n g i n j e c t i o n and e j e c t i o n devises. The elements produces p e r t u r b a t i o n , d i f f e r e n t i n every sector. I t i s necessary t o c o r r e c t t h i s p e r t u r b a t i o n i n order t o o b t a i n i d e n t i c a l sectors (see fj 4.2.6.).

The f o u r sectors magnets are equiped w i t h s i d e shims ( f l a i r e d poles) g i v i n g a y = 1.00 f i e l d map f o r SSCl and y = 1.05 f o r SSC2. To a d j u s t t h e f i e l d f o r any y v a l u e (from 1.00 up t o 1.05 i n SSCl and from 1.05 up t o 1.1 o r down t o 1.00 f o r SSCZ), a s e t of p o l e face winding, c a l l e d t r i m c o i l are used.

3.2 - bllgnet-yealjdatjpn 3.2.1 - C u t t i n g pf-the-magnet

Each sector, weighing 425 tons, has been d i v i d e d i n t o 10 pieces by h o r i z o n t a l c u t t i n g .

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3.2.2 - _St_eel g u a l j t y 3.2.2.1 - The yoke m a t e r i a l ...

The s t e e l o f t h e d i f f e r e n t pieces o f t h e yoke i s coming from vacuum c a s t i n g o t s . The i n g o t s a r e f i r s t precrushed w i t h a press and then r o l l e d (average chickness o f t h e pieces 600 mn).

3.2.2.2 - The poles m a t e r i a l ...

The poles are forged u s i n g vacuum c a s t i n g o t s . The carbon content i s 0.015 %. We have measured the curve B(H) on r i n g samples. The standard d e v i a t i o n TB f o r d i f f e r e n t value o f B a r e :

H 240 800 1250 3000 8000 13000 19000

B 1.2848 1.562/ 1.6098 1.6922 1.8192 1.9014 1.9878

0.0005 0.0004 3.2.3 - kJechgnjcal-desjgn

The mechanical s t r u c t u r e o f t h e magnet i s a simple p i l e o f 10 pieces w i t h o u t any b o l t s between them. The magnet has been assembled j u s t by stack- i n g p a r t s .

A gap o f 10 mm i s managed between each p o l e and the corresponding yoke. Through t h i s gap passes a s k i n which i s a p a r t o f the vacuum chamber. See F i g u r e 6.

A t r h r e e p o i n t s of t h i s s k i n a r e mechanical devices (see Fig. 6 ( 1 ) ) composed o f : bellows g i v i n g t h e necessary f l e x i b i l i t y between magnets and vacuum chamber ( e ) ; p1 a t e s t r a n s m i t t i n g the f o r c e s ( f ) ; v e r t i c a l p i n s w i t h t i g h t - ness (g). The t h i c k n e s s o f the p l a t e s w i l l be adjusted t o

.Fig. 4 : i s o m e t r i c view o f SSC

F i g . 6 : (1) View o f t h e p o l e showing - m a i n c o i l ; (b) t r i m c o i l s ;

( c ) s i d e shim ; ( d ) s k i n ; ( e ) bellows;

( f ) p l a t e ; ( g ) v e r t i c a l p i n ;

( 2 ) t h e f r o n t spacer.with.horizonta! pin;

( 3 ) conductors o f t r i m c o i l s i n t h e i r casing.

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Cl-198 JOURNAL DE PHYSIQUE

b r i n g t h e p o l e complex and the r e t u r n yoke t o e x a c t l y t h e same h e i g h t .

The u s e f u l gap i s d e f i n e d by t h r e e spacers c u t along t h e mid plane. The spacer halves a r e - b o l t e d d e f i n i t e l y t o each pole, the c o a x i a l i t y between poles w i l l be obtained by h o r i z o n t a l p i n s between these two halves. See F i g . 6 ( 2 ) : Specified t o l e - rances are 0.05 mm f o r p l a n a r i t y and 0.1 mm f o r p a r a l l e l i s m o f the poles surfaces.

The magnetic f o r c e s ( a t t r a c t i o n between t h e poles i s 600 tons) induce spacers' compression : 0.08 mm on f r o n t spacer and 0.06 mm on r e a r ones.

The assembly of t h e magnet i s a simple s t a c k i n g of t h e t e n pieces, w i t h o u t b o l t s , t h e cohesion o f which i s g i v e n o n l y by weight and magnetic forces. This c o n s t r u c t i o n technique was p o s s i b l e on account o f t h e v e r y good accuracy o f t h e machining o f t h e surfaces. A care- f u l l measurement o f the h e i g h t H has been made before t h e i n t r o d u c t i o n o f

t h e p o l e complex. Adjustment o f t h e WLE COMPLEX 1 I I

mechanical shims which define the _YOKE

d a m ~ i n q - - . gaD were made t a k i n g i n t o account the measured v a l u e s - o f H

(Fig. 7). Fig. 7 : Magnet mechanical adjustment.

The u s e f u l gap i t s e l f i s d e f i n e d b y t h r e e s t a i n l e s s s t e e l spacers which ensure q u i t e p a r a l l e l p o l e surfaces.

3.3 - cgjls-ye.ljzatjpn

3.3.1 - !hp gajn-coi]s-and-thejr-vacu_uy-tight b o x e l

The main c o i l s o f t h e f o u r s e c t o r s o f one c y c l o t r o n a r e s u p p l i e d i n series, e q u a l i z i n g c o i l s (+ 2 %) being e x c i t e d s e p a r a t e l y : ( t h e e l e c t r i c a l data o f the main c o i l a r e : number o f t u r n s : 56 ; h o l l o w conductor s i z e : 20 X 20 m 2 ; h o l e : 9.11 mm ; maximum c u r r e n t : 1850 A ; power : 120 kW ; c o o l i n g water f l o w : 10 m3/h).

The c o i l i s c l a s s i c a l b u t f o r vacuum reasons, i t must be s e t i n a vacuum-tight s t a i n l e s s s t e e l box which w i l l be soldered a f t e r impregnation. See F i g . 6.

3.3.2 - ^!he trjm-coils-and-their-vacgum t i g h t casing Each pole face winding has 32 c o i l s (see Fig. 11).

. 5 c o i l s , o f one turn, type N, f o r c o r r e c t i o n o f i n j e c t i o n d e f e c t s

. 6 c o i l s of one turn, type B, f o r c o r r e c t i o n o f s e c t o r t o s e c t o r d i f f e r e n c e s and e j e c t i o n d e f e c t s

.

21 c o i l s of two turns, type I, c a l l e d "isochronism c o i l s " s u p p l i e d i n s e r i e s from s e c t o r t o s e c t o r and used t o a d j u s t t h e f i e l d shape.

53 conductors a r e so t a k i n g p l a c e i n a h a l f gap. They a r e f o l l o w i n g t h e e q u i v a l e n t t r a j e c t o r i e s "Gordon Hard Edge". The maximum i n t e n s i t y i s 200 A. For one sector, the power consumption i s 2 X 12 kW and t h e average temperature e l e v a t i o n i s 10°C. Each p o l e face winding uses 565 m of a conductor manufactured by Pyrotenax w i t h the f o l l o w - i n g parameters : o u t e r dimensions : 8 X 8 mm ; c e n t r a l conductor : 6 X 6 mm2 ( t h e thickness o f mineral i n s u l a t i o n s i s 0.70 mm).

A f t e r shaping t h e p o l e face windings are enclosed i n vacuum t i g h t casings t o ensure i n s u l a t i o n from t h e machine vacuum. The casings a r e subjected t o an i n t e r n a l pressure equal t o atmospheric pressure. They are made of a p l a t e and of a c l o s i n g welded upon it. (See Fig. 6 ( 3 ) ) .

4 - MAGNETIC MEASUREMENT OF SSC

4.1 - Magnetic-measuremepts-ape?rr?t!-s

The magnetic f i e l d has been measured i n t h e gap mid plane by 90 Hall probes. The device covers the r a d i a f e x t e n t from 840 mm t o 3220 m and t h e azimuthal e x t e n t 0" - 360" w i t h a step of one degree.

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The H a l l probes are Siemens SBV 601-S. They a r e s t a b i l i z e d a t a temperature o f 35 + O . l ° C and p r e l i m i n a r i l y c a l i b r a t e d ( 7 t h order polynomial approximation). The H a l l v o l t a g e has been measured by a Schlumberger S o l a t r o n 7075 v o l t m e t e r ( t i m e constant : 200 ms).

The measuring arm i s mounted on a movable r i n g displaced, step by step, by a pneunla- t i c device. The p o s i t i o n i s given by machined groves and read by a pneumatic sensor.

Measurements a r e performed every degree (32400 values f o r a 360" map a r e obtained i n 4 hours). P r e c i s i o n i s b e t t e r than + 1 Gauss on the whole range o f f i e l d l e v e l (0.66 t o 1.75 T).

A M i t r a 125 on l i n e computer i s used f o r data a c q u i s i t i o n and pre-treatment and f o r arm displacement monitoring.

4.2 - M a j n ~ - y e l u l t l 4.2.1 - Mechgnjcal-behavjogr

The computed mechanical behaviour has been v e r i f i e d : w i t h B = 1.7 T t h e forces i n t h e spacers have been measured (2.103 kN i n t h e f r o n t spacer and 2.5 103 kN i n each o f t h e two r e a r spacers) ; li k e w i s e have been v e r i f i e d the gap deformation ( d <

0.15 mm) and the r a d i a l displacement o f t h e upper nose (Ar = 0.2 mm).

4.2.2 - Identi_ty-of l e c t o r s

F i e l d shapes i n the f o u r sectors o f a machine are t h e same b u t absolute l e v e l s a r e s l i g h t l y d i f f e r e n t : f o r example, i n SSC1, we have f o r a main f i e l d o f 1.6 T :

Sectors --- A ^{- m - -}B -I-1 C ^D

AB - 4 3 G + 7 7 - 6 0

t h e r e f o r e t h e measured AB a r e i n t h e o r d e r of 5.10-j, h a l f o f t h i s v a l u e i s coming from s t e e l p r o p e r t i e s d i s p e r s i o n and h a l f from gap mechanical d i s p e r s i o n . An a u x i l i a r y c o i l o f each magnet compensates f o r t h i s e f f e c t .

4.2.3 - F i e l d mappjng y i t h g u t j n i e c t j o n elements

Magnetic f i e l d mapping w i t h o u t i n j e c t i o n elements gives v e r y good f i e l d shapes : t h e average f i e l d deviates by l e s s than 20 gauss from the t h e o r e t i c a l isochronism law f o r which t h e p o l e s i d e p r o f i l e s were designed ( y = 1.00 f o r SSC1, y = 1.05 f o r SSCZ).

A l l the r e s u l t s o f t h e magnetic measurements a r e described i n i n t e n a l r e p o r t s

(. 4 ) . L e t us consider some r a t i o s which ,,,,,,, ,,,,,,,., ^{Fig. 8}

a r e s i g n i f i c a n t o f the behavior o f t h e h /i~aussl

f i e l d versus radius, f o r 6 d i f f e r e n t

l e v e l s o f f i e l d . .- 2s

F i r s t , consider the d i f f e r e n c e between B, f o r every r a d i u s and BBxis f o r R = 2.34 m. The f i g . 8 ( a ) gives a x i s ( R ) -

B a x i s (2.33 m) versus R.

Secondly, consider t h e average f i e l d B

f o r each value o f R, and consider t h e r a t i o K b = Baxis/B. The f i g . 8 ( b ) g i v e s Kb versus R. This r a t i o i s used f o r the magnetic f i e l d s e t t i n g (Chapter 5).

4.2.4 - F i e l d mappjng y i t h - i n j e c t i p n

c l em$n_ts-

The f i g . 9 shows f o r each s e c t o r of SSC2 t h e e f f e c t s o f i n j e c t i o n elements on t h e mean f i e l d (Case Bmax % 1.6 T).

4.2.5 - Shjming-for-lgcal-cgmpefisatjon i n j e c t i o n and e j e c t i o n devices ( M i l , Mi2, SMi3, SMi4, MSe2, Mse3, Me5 and Me6 which w i l l be described i n Chapter 6 ) change t h e f i e l d by g i v i n g , compared t o t h e unperturbed one, n o t o n l y mean f i e l d e r r o r s 68 b u t a l s o composents 6(aB/ae) which a f f e c t s t r o n g l y t h e o r b i t s .

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Cl-200 J O U R N A L D E PHYSIQUE

5 - MAGNETIC FIELD SETTINGS FOR RUNNING WITH BEAM 5.1 - Procedure-of-the-rnngne_t1ccf1e1d-sett1!g

Using magnetic f i e l d measurements on SSC's and o r b i t c a l c u l a t i o n s , we proceed i n t h e f o l l o w i n g way t o o b t a i n a f i e l d s u i t a b l e f o r a given case o f a c c e l e r a t i o n : ( 5 - l )

- a c y c l i n g procedure i s done on t h e main magnet t o g e t a good r e p r o d u c i b i l i t y o f t h e f i e l d p a t t e r n ;

- t h e i d e n t i t y between t h e f o u r sectors i s ensured by a d j u s t i n g a u x i l i a r y c o i l s t o o b t a i n t h e same f i e l d l e v e l a t the reference a x i s r a d i u s of 2.330 m and by u s i n g independent "nose" c o i l s on each s e c t o r t o cancel the remaining p e r t u r b a t i o n GBcor due t o the i n j e c t i o n devices. The l a r g e s t p e r t u r b a t i o n s measured on A and D sectors, have been p a r t l y compensated by a l o c a l s h i m i n g i n SSC l (g 4.2.5) a l o c a l s h i m i n g p l u s a p o l e p r o f i l e m o d i f i c a t i o n i n SSC 2. So, a u x i l i a r y and "nose" c o i l s a r e used t o g e t the same average magnetic f i e l d on t h e f o u r sectors and t o be as close as p o s s i b l e o f the B (R) law i n unperturbed sectors.

- isochronism law r e q u i r e d t o a c c e l e r a t e a given p a r t i c l e i s tuned by means o f 21 c o i l s o f 2 t u r n s each i n s e r i e s i n the f o u r sectors and s u p p l i e d by 1 2 power supplies as shown on f i g . 11.

5.2 - Me_thgd-gf-~sgchyp!jzatjg_n

The method o f i s o c h r o n i z a t i o n developped and t e s t e d d u r i n g magnetic measurements, has been t e s t e d w i t h beam. L e t us j u s t r e c a l l i t s main l i n e s and advantages (5.2).

For a p a r t i c l e accelerated a t the frequency frev (A, Q and frev given), the average magnetic f i e l d B needed a t t h e mean r a d i u s R i s given by :

Ue then decide t o compensate t h e most p e r t u r b i n g elements, namely ivii2, Slvli3 and Me5 as near as p o s s i b l e t o t h e p e r t u r b a t i o n they introduce. To do t h a t , we determine e x p e r i m e n t a l l y e i t h e r l o c a l p l a t e shimming (SCC1) o r a combination o f p l a t e shimming and p o l e p r o f i l e m o d i f i c a t i o n (SSC2).

F i g u r e 10 shows the compensation system o f Mi2 and SMi3 i n s e c t o r A l of SSC 1.

A f t e r c o r r e c t i o n , i t remains a r e s i d u a l p e r t u r b a t i o n which, i f acceptable on gradients, has t o be c o r r e c t e d i n mean f i e l d . From measurements a t the 6 l e v e l s , we know f o r each s e c t o r the 6B t o be c o r r e c t e d and we can i n t e r p o l a t e a t o t h e r l e v e l s . A small computer code gives t h e s e t o f c u r r e n t s IF which cancels t h e 6B.

4 AE SSC1 Sector A perturbed by Mi2-SMi3

2 0 0 -

! ₃ - c n l $ 4 O -! 9 1 1.1 1.2 43 P m

L - ^{o n 1 2} ^$ ⁶

--l0 .--

_

^C

G a s s

, FIELD PERTURBATDNS Curve A : Initial perturbation

2 -'

FROM INJECTION DEVICE B: Rernainning perturbation when

corrected by shim

I 1 Secter A M W i 3 effects

I l a - A Hi2 dors . ^{* A B} C : Compensation of remalnning.

Ib - ^A S H 3 a b r p ; Gauss perturbation by trim coils

2 - ^B^SUi4.Hi2 ^t ⁶ ^l

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- B (W) = A,, 1 R

g C 2 B Y = with 13 = 2 n f r e v t a n d y =

1

R (1 - B2) 1/2 (1)

Non accelerated closed o r b i t s have been computed on complete f i e l d maps measured a t s i x reference levels t o obtain the c h a r a c t e r i s t i c r a t i o s which a r e function of Raxis :

Kb = Baxis/B and Kr = Raxis/R

Using these 2 experimental r a t i o s and formula ( l ) , isochronous magnetic f i e l d law along the sector axis i s given by :

Amo C 2 2 frev. Y. Kb With = 2 n Raxis frev

Biso (Raxis) = -Q---- . _C _Kr _'₇

As we have measured the magnetic f i e l d along the sector axis on unperturbed sectors

B a x j s (Raxis) a t the s i x reference l e v e l s , the trim coil contribution ABTC t o obtain isochronism i s given by :

ABTC (Raxis) = Biso (Raxis) - Baxis (Raxis)

Taking into account the actual trim-coil pattern, t h e i r c h a r a c t e r i s t i c s and the number of power supplies, the control matrix T giving the magnetic e f f e c t along the sector axis f o r a given trim-coil current has been calculated with the program BOB0 ( 5 . 3 ) . Using as input data the matrix T and a l e a s t square method a small computer code gives, in a few seconds, the trim-coil currents needed t o obtain the desired curve ABrc(RaXis). This method i s very a t t r a c t i v e because i t needs very few memory locations t o s t o r e i t s datas and the code i t s e l f i s very small and f a s t .

power C ~ l I d ~ c t ~ s w l y

12 11 10 9 8

7 _ _ - - - . - --

_ _ _ . - - - . - . - - .

.-- ^__.--

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l

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- c o n M W 5 J used for modrnkr(in series for m. 4 arcton!,

r e & c t o r a n ('nose" c d : d for hj.rtan p a t v ~ h

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---. ... &m c m h d php. NW. d&d Bean cartrd phase t k t u y v- nd*l

Isochronism coil Loop "Wmc"ul

21 co~ls o f 4 coils of 5 coils of Ial : with pnd0dat.d triwd .*W

2 turns each 1 turn each 1 turn each ^(bt: a f t s nr i t a r t i n of *oil -h

(C! : aft- a IMd ilslla of n* t r C u l l c u t n h .

Fi g. l l ^::lay out of trkninp coils

Using the magnetic data-table a code computer f o r a given p a r t i c l e and energy :

- the required f i e l d level on the sector axis a t the reference radius of 2.330 m and the associated currents f o r the main and the a u x i l i a i r y c o i l s . (Hall probe in s i t u f o r each sector i s located a t R = 2.33 m)

- the currents i n the "nose" c o i l s t o cancel the remaining injection perturbation on each sector

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Cl-202 JOURNAL DE PHYSIQUE

- t h e c u r r e n t s f o r isochronism c o i l s u s i n g t h e method described i n 5.2.

The p r e c a l c u l a t e d t r i m - c o i l c u r r e n t s values a r e used t o s t a r t t h e machine and a r e acurated enough t o a c c e l e r a t e t h e beam up t o t h e e x t r a c t i o n radius. Then t h e i s o - chronism l a w i s adjusted w i t h an o n - l i n e r o u t i n e u s i n g t h e beam c e n t r a l phase measurements.

5.4 - ?n:Llne-lsochronlznt1on-b~~benm~~entra1-~hass-mea1ursm:n~s

Using the h i g h l e v e l f a c i l i t i e s o f t h e GANIL c o n t r o l system (5.4) and a performant beam c e n t r a l phases measuring device, an i n t e r a c t i v e r o u t i n e has been developped t o r e f i n e a u t o m a t i c a l l y the isochronism i n t o t h e SSC. The u s e r ' s t a s k named ISOGRO (5.4) i s w r i t t e n i n LTR and runs on t h e GANIL c o n t r o l computer, a MITRA 125. The beam c e n t r a l phase h i s t o r y versus t h e r a d i u s i s obtained by t h e 15 c a p a c i t i v e electrodes l o c a t e d along one v a l l e y a x i s o f t h e SSC from the i n j e c t i o n o r b i t t o the e x t r a c t i o n o r b i t .

The beam c e n t r a l phase curves measured a f t e r each step o f t h e i s o c h r o n i z a t i o n procedure a r e shown on F i g . 12 (a, b, c ) . Only few i t e r a t i o n s on t u n i n g t h e t r i m - c o i l s c u r r e n t s l e a d t o t h e d e s c r i e d c e n t r a l phase law f i t t e d w i t h i n + 2 degrees.

5.5 - s ~ j f t - g f - f h ~ - m a g n g t j c c f jeld

During t h e r u n i n g o f t h e accelerator, i t appears a s h i f t o f t h e magnetic f i e l d f o r a constant c u r r e n t o f t h e power-supply. T h i s s h i f t appears m a i n l y d u r i n g t h e two o r t h r e e f i r s t days o f running. This i s due t o t h e h i g h weight o f the magnet (500 tons each s e c t o r ) . The consequence o f t h i s e f f e c t i s e v i d e n t l y t h e s h i f t o f the phase.

Consider t h e 4e and 4s (entrance and e x i t phase). The d i f f e r e n c e 4s - @e i s measured, as feedback system uses t h i s value f o r a d j u s t i n g t h e c u r r e n t o f the main c o i l s power- supply, i n order t o m a i n t a i n t h e 4s - Qe constante.

6 - INJECTION AND EJECTION SYSTEM

The I n j e c t i o n and E j e c t i o n systems are m a i n l y composed o f magnetic elements ( 6 ) (See F i g . 5). Magnets H i l , Mi2, Me5, Me4 are o f window-frame type, f o r b e t t e r perfor- mance. Mi2 (See F i g . 13) can reach 2 t e s l a w i t h no s i g n i f i c a n t change of magnetic q u a l i t y .

F i g . 14 ⁰

Septum magnet SMi3 (Fig. 14) i s made o f a c o i l l o c a t e d between two p a r a l l e l p l a t e s , t a k e s advantage o f t h e main f i e l d t o provide and i n d u c t i o n along i t s a x i s which can reach 2 Tesla. The c o i l i s needed f o r small adjustments i n any case. But i t has been m a i n l y designed t o compensate f o r t h e hexapolar effect of t h e p i e c e o f i r o n ( F i g . 15).

As can be seen from f i g . 16, t h e combined e f f e c t o f c o i l and i r o n can be arranged i n such a way as t o p r o v i d e a good homogeneity of t h e f i e l d i n the h o r i z o n t a l and v e r t i - c a l d i r e c t i o n . Note t h a t if t h e t o p and t h e bottom conductor o f t h e main c o i l had been off s e t by 1 mm ; in s t e a d of 3 mm as shown Fig. 27, optimal homogeneity would have been achieved. Fig. 9 shows the f i e l d perburbation e x t e r n a l t o i n j e c t i o n elements.

This p e r t u r b a t i o n has been compensated by shims made o f two p a r a l l e l p l a t e s o f i r o n o f 2 mm thickness (See g 4.2.5).

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The Ejection c o i l s We2 and Me3 a r e designed t o provide a maximum of 0.02 Tesla, opposite t o the main f i e l d . The perturbation produced by these c o i l s in t h e i r v i c i n i t y are of the same polarity as the main f i e l d and have t o be compensated by the means of trim-coil ^S.

* B (Tesla) Hight induction

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0 1 2 3 4 5 6 7 , 8 9 1 0

:Combined effects of c o ~ l and Iron.

7 - ^BEAM^LINES

The GANIL's beam l i n e a r e 250 m long. I t consists of two main parts : the beam l i n e of the "Accelerators" located in the Machine building and the beam l i n e of the Expe- rimental area located in the Experimental Area building ( 7 . 1 ) .

7.1.1 - ~ g ~ ~ - l ~ ~ ~ - g f - ~ h g - ~ ~ ~ g ~ g ~ a ~ ~ ~ ~ ( I The Accelerator beam l i n e consists of three sections (See Fig. 1 ) : L 1 (from C01 or C02 t o SSCl), L2 (from SSCl t o SSC2) and L3 (from SSC2 t o entrance of the Experimental a r e a ) . The beam i s analyzed between the injectors and SSCl (L1 l i n e ) . The SSCl and SSC2 work generally together with a s t r i p p e r between (the s t r i p p e r increases the charge of the p a r t i c u l e s ) , but the design allows the running of each SSC alone (mode solo). We l i m i t and measure the energy spread, with an spectrometer called "alpha spectrometer". I t consists of four wedge bending magnets, quadripoles, sextupoles.

The energy spread i s kept down t o +- 2.5 . l O - * . ( 9 )

7.1.2 - ~ ~ ~ ~ - l j ~ g - g f - $ h g - ~ ~ p g ~ j ~ g ~ ~ a ~ - a ~ _ e ~ ~

The beam l i n e of the experimental area consists of a s t r a i g h t central beam l i n e and bending magnets deflecting the beam t o eight caves where experimental devices are i n s t a l l e d . Each deviation consists of two identical 30" pulsed bending dipole w i t h a symetric quadri p01 e t r i p1 e t between them.

7.1.3 - pulsgd-ijeomgs

The pulsed dipole magnets are used t o send the beam to the d i f f e r e n t experimental rooms. Two users can be served in the same time one being the main user, the other being a secondary user. For t h a t purpose, the dipole are pulsed according t o the following time cycle. Over 10 seconds :

- high level during 8 seconds the beam i s deflected t o the room ;

- zero level during 1 second the beam goes s t r a i g h t ;

- twice 500 m sec. a r e l o s t f o r going u p ( o r down) and g e t the f i e l d s t a b l e to The main c a r a c t e r i s t i c s of the magnets are : the dipole i s a H-type with non satured non profiles. A pole p r o f i l e end has a shim t o allow the adjustment of the magnetic length. The f i e l d speed i s 5 T/sec. On the zero l e v e l , the rernanent f i e l d i s compensated by a small negative current.

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C 1-204 JOURNAL DE PHYSIQUE

The s p e c i a l e l e c t r i c a l supply i s a b l e t o g i v e : -+ 850 Amps and - 10 Amps i n t h e same c o i l .

The bending magnets, o f H s t r u c t u r e , a r e conventional ones, w i t h u n i f o r m f i e l d and wedge focusing. These d i p o l e s are o f s i x types :

D e f l e c t i o n ir 30" 43,5" 60" 65" 67,s" 90"

Number ... ^-⁷4 2 -4 2

Magnetic r a d i u s (mm) ... ⁷⁵⁰ ⁷⁵⁰ ⁷⁵⁰ ¹⁸⁰⁰ ¹⁸⁰⁰ 7 50

Gap (mm) ... ⁶⁵ ⁶⁰ ⁶⁵ ⁵⁵ ⁵⁰ ⁶⁰

Useful area tmm) ... ^-+ ³⁵ ³³⁰ ^ir³⁵ ³³⁰ ^ir + ⁶⁰

AB ... ^1,6.10-41,2.10-" 1,6.10-",6.10-4

- 1,6.10-"

R ...

Max i n d u c t i o n (T) 1,l 1 ,I lY1 1,6 1.6 1,1

Entrance f a c e ... ^30" 21,75" 17,5° 15" 18" 26,56"

E x c i t face ... ^O0 21,75" 17,5O 15" 18" 26,56O

Radius face ... ^m ^m ^m ^m ^m ^2,57m

Max c u r r e n t ( A ) ... ⁴²⁰ ³⁹⁰ ⁴²⁰ ⁵⁴⁰ ⁵²⁵ ⁴⁰⁰

...

Power consumed (kW) 26 24 31 60 60 3 5

T o t a l mass (T) ... ^1,4 ^1,4 ^1,5 ⁸ ^10,5 ³^,5

The main elements have been determined ( u s i n g MAGNET code), i n o r d e r t o o b t a i n t h e f o l l o w i n g p r o p e r t i e s : r a d i a l homogeneity, magnetic l e n g t h quasi independant o f f i e l d induction, magnetic l e n g t h i d e n t i c a l t o mechanical length.

These p r o p e r t i e s have been r e a l i z e d by t h e use o f one o r two level-edges.

For L1041 (90") whose f u n c t i o n i s low energy spectrometer, the ends have a l s o a geometrical curvature.

The magnetic f i e l d i s measured i n t h e midplane by mean o f a c a r r i a g e of 21 h a l l probes d r i v e n by step motors.

The whole 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.

155 quadrupoles a r e l o c a t e d i n t h e beam t r a n s f e r system. I n order t o minimize t h e s e r i e s o f magnets, we have grouped t o g e t h e r elements w i t h a d j a c e n t g r a d i e n t values i n t h e same series. Seven types o f quadrupoles have been so defined.

TYPE 1 2 3 4 5 6 7

Number ... ⁴ ⁶³ - 7 - 1 3 7 - -

Aperture (mm) ... 55 70 70 80 80 100 140

Max g r a d i e n t (T/m) .. ²⁰ ¹³ ²⁰ ⁸ ²⁰ ⁸ ⁶

Homogeneity ... ⁴ Z.10-3 2.10m3 2.10-3 2.10-3 2.10-3 2.10-3 2.10-3

Length (mm) ... ¹⁵⁰ ³⁰⁰ ³⁰⁰ ³⁰⁰ ³⁰⁰ ³⁰⁰ ³⁰⁰

Max c u r r e n t (A) ... ²⁵⁰ ¹⁶⁵ ²⁶⁰ ¹²⁵ ³¹⁰ ¹⁶⁰ ¹⁸⁵

...

Power (Kw) 3 3,5 7,8 2,2 11,7 5 7

For the r e a l i s a t i o n o f these quadrupoles, we have chosen a design w i t h a square yoke.

The p o l e p r o f i l c o n s i s t s of an h y p e r b o l i c section, extended by two s t r a i g h t p a r t s optimized w i t h MAGNET p r o p e r t i e s . The c o i l s are b u i l t w i t h h o l l o w conductors o f a square section.

7.2.3 - I h e pujsed-djpgle magnets

The d i p o l e i s described i n d e t a i l s i n a c o n t r i b u t i o n (7.2). The laminations a r e 1.5 mm t h i c k . To a v o i d Eddy c u r r e n t e f f e c t s i n the ends, we have chosen.

( i ) v e r y t h i n end p l a t e s : 10 mm

( i i ) no s a t u r a t i n g p r o f i l e .: h i g h p value.

For machining the p r o f i l e , the l a m i n a t i o n s i n t h e ends were s t r i k e n i n a l l c e n t r a l p a r t o f t h e magnet t h e laminations were o n l y welded o u t side. No b o l t was used.

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8 - EXPERIMENTAL AREAS

The experimental areas consists of 10 caves, supplied by 8 beam deviations (Fig. 1 ) . W shall describe only the caves using special magnet design. e

G3 cave will house a large spectrometer called SPEG (Spectrometer f o r GANIL) schedu- led f o r 1984 (8.1). On Fig. 1 are shown the main magnetic elements. On the beam l i n e , s t a r t i n g from an object point down t o the t a r g e t position, one will find three quadripoles, one dipole (the analyser magnet), again two quadripoles, two sextupoles. Beyond the t a r g e t , the spectrometer will c o n s i s t of one quadripole, one sextupole, two d i - poles (spectrometer magnet) and one quadripole. The analyser i s a window frame type with incl ined entrance face. The spectrometer dipoles c o n s i s t s of 2 identical C-type magnet. The analyser and spectrometer a r e equipped by mechanical pole face shims and e l e c t r i c a l pole face shims (8.2). A Modcomp on-line computer i s used f o r date acqui- s i t i o n and pre-treatment and f o r arm displacement monitoring. The magnetic measurements of t h e Analyser magnet has noted t h a t the entrance lenses of the spectrometer, one quadripole and one sextupole are equipped with an open return yoke.

D3-D4 cave will house the super-stripped ion l i n e (LISE) f o r atomic physics. This l i n e consists of two quadripoles, one dipole, four quadripoles, one dipole and four quadri p01 e s .

D5 cave will house a mass spectrometer and i r r a d i a t i o n i n s t a l l a t i o n f o r condensed matter physics. In order t o display a beam on a t a r g e t , we use two quick pulsed d i - poles ( r i s e time = 2 ms) producing two perpendicular deviations along X a x i s and Yaxis.

The screen located a t 3 meters from the dipoles must be i r r a d i a t e d inside a rectangle of 20 X 30 mm dimensions. These special dipoles made with s i l i c o n iron plates of 100 pm thickness a r e under construction.

REFERENCES :

(1) J . FERME, M. GOUTTEFANGEAS and GANIL Group, 9G ICCA (9th International Confe- rence on Cyclotrons and t h e i r Applications), CAEN, 1981.

(2) M.P. BOURGAREL and a l . , 86 ICCA, BLOOMINGTON, 1978.

(3) D. BIBET, A. DAEL, M. OHAYON, 86 ICCA, BLOOMINGTON, 1978.

( 4 ) Internal GANIL Reports : mesures magnetiques sur l e s CSS, 80R/104/TP/03, 81R/022/TP/03.

(5.1) J. SAURET and GANIL Group : Magnetic f i e l d s e t t i n g and automatic isochronization.

PROTVINO, URSS, 1982.

(5.2) A. CHABERT, Isochronisation du champ dans l e s CSS, GANIL 81R/071/TP/04.

(5.3) D. BIBET, A. DAEL, Programme BOB0 pour l e calcul des courants dans l e s Trim- Coils, GANIL 77N/078/AI/19.

( 6 ) J. FERME and a l , Injection and Ejection System, 7th ICCA, ZURICH, 1975.

(7.1) R. ANNE and a1 ., GANIL beam l i n e s , 8th ICCA, CAEN, 1981.

(7.2) M. DUVAL, A. DAEL, Pulsed magnets f o r GANIL, This Conference (8) J . GASTEBOIS, SPEG, Spectrometer f o r GANIL, DPh-N/BE, CEN, SACLAY.

(9) M. REBMEISTER Internal reports (alpha - spectrometer).