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Status report on the GANIL facility
A. Joubert
To cite this version:
A. Joubert. Status report on the GANIL facility. Tenth International Conference on Cyclotrons and
their Applications, Apr 1984, East Lansing, United States. pp.3-10. �in2p3-00996336�
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STATUS REPORT ON THE GANIL FACILITY
A. Joubert and the GANIL Group
GANIL - CAEN - FRANCE
V
STATUS REPORT OH THE GAIfIL FACILITY
CAIJIL has been f u l l y o p e r a t i n g for 16 nonths for Nuclear Physics ( 9 0 S ) , a t o n i c and s o l i d s t a t e p h y s i c s . Hore than i&OQ hours of e f f e c t i v e beam t i n e were d e l i -vered to t h e e x p e r i n e n t s u n t i l April I98fc. The œaximua p a r t i c l e i n t e n s i t y reached i n o p e r a t i o n i r Ii 10 pps of U 0A r '6 + a t Ul MeV/A and 1.2 1 0, 2p p s of l 608 + a t
9U KeV/A. Beans of Oxygen, Argon , C a l c i u a , Neon and Krypton have been s u c c e s s f u l l y t e s t e d and used for ex-p e r i m c t s . At UU MeV/A t h e Ar beam i s sent to t h e physics t a r g e t with t h e following measured c h a r a c t e r i s -t i c s : r a d i a l emi-t-tar.ce : £ . = 6 raa.mrad, r = 3 nnxi.m-nd, energy spread ( t o t a l width) : ÛH/H = 10 ' a t l»50er.A , length of t h e RP beara pulse3 ; "\> 1 n s . The GAHIL f a c i l i t y and t h e improvements aade during th;; f i r s t o p e r a t i o n y e a r a r e d e s c r i b e d . The a l t e r n a t e i n -j e c t o r (a s r a l l conpact c y c l o t r o n i d e n t i c a l t o t h e f i r s t o n e ; w i l l be i n o p e r a t i o n i n 196^ with an i n t e r
-n a l PIC sourc
an a x i a l i n j e ;. I t should be run :tion i n 1965. ' i t h an ECR source (
1. IHTaODUCTIOH
D e t a i l e d d e s c r i p t i o n s of GANIL ( Grand Accéléra-t e u r NaAccéléra-tional d ' I o n s Lourds! have been already given i n s e v e r a l previous conferences * ' , F i g . 1 r e c a l l s i t s general layout i n c l u d i n g t h e present expérimental a r e a c o n f i g u r a t i o n «here 8 caves a r e in use f o r experiments. The a c c e l e r a t o r complex i s a combination of 2 p a r t s :
a . P r e s t r i o p e r p a r t ;
- A compact c y c l o t r o n CO as i n j e c t o r (K = 30) with an i n t e r n a l PIC s o u r c e .
A s e p a r a t e d function bean t r a n s f e r l i n e Lt i n -c l u d i n g a low energy spe-ctrometer and a rebun-cher R1.
- A k s e p a r a t e d s e c t o r c y c l o t r o n S5C1 (K = UOO). MASS SPrcTPDMCTER Be JCT HOi-NucicAK PHYSICS GPCCTROMCTCH Î T R A / S T U D I E S W f l t K - l W S C I * CHUMBCK + PLASTIC WALL arcoNp tu*ECTQR AXIAl. IMJFlTlal /<"»
ECfl IO*J SOUKCf 0 * 8 5 )
ta. FOST.S t r i p p e r p a r t - A beam t r a n f e r l i n e L2 i n c l u d i n g a Carbon f o i l s t r i p p e r . - A it s e p a r a t e d s e c t o r c y c l o t r o n SSC2 i d e n t i c a l t o SSCI. - A beaa t r a n s f e r l i n e L3 i n c l u d i n g a oonochroma-t o r .
The bean i s then conducted and i s time shared by means of pulsed magnet3 t o 2 physics experiments.
The f i r s t ion beam { Ar ) from SSCI was obtained i n June 1982. A f u l l energy Ar * bed.ii a t Ub MeV/A vas a c c e l e r a t e d i n SSC2 and e x t r a c t e d 5 months l a t e r ( i n November 19o2). The beam va3 d e l i v e r e d to t h e p h y s i c i s t s i n January 1983.
2. OAHIL CHARACTERISTICS AMD BEAM OPERATIHC RESULTS 2.1 General parameters
F i g . 2 shows t h e basic c h a r a c t e r i s t i c s of t h e beams i n t h e range of r e s o n a t o r frequencies for two com-b i n a t i o n s of a c c e l e r a t i o n harmonics. The com-beams a l r e a d y t e s t e d have been p o i n t e d .
The main GAJIIL measured c h a r a c t e r i s t i c s a r e sum-• - r i z e d iii t h e following t a b l e s 1,2,7 for t h e 3 energy l e v e l s a l r e a d y l.ested : Argon a t 27 HeV/A and hU MeV/A, Oxygen a t ?li HeV/A (max v a l u e ) .
1*0. U* x RF f r e q u e n c y (MHz) 7 . 6 9 . 5 S 1 3 . 3 7 INJECTOR It It It RF h a r m o n i c n u m b e r It It It RF v o l t a g e kV 30 6 0
°3
[lumber o f a c c e l e . t u r n s lL. ll» 11* M a g n e t i c f i e l d T 1 . 2 3 l-5*i i . i 6 E x t r a c t e d beam e n e r g y MeV/A • 15 . 2 5M
Beam r i g i d i t y T . m • 5T . 7 2 . 5 b I o n s o u r c e d u t y c y c l e . 2 5 t o . 5 p u l s e w i d t h D 3 I t o 5 E x t r a c t e d t e a m i n t e n s i t y 1 01 Jp p s 6 6 10 ( t y p i c a l ) eiiA •\Jj-u*
-V5 E n e r g y s p r e a d - r r ( t o t a l w i d t h )to"
2 1 . 3 1 . 3 1.1» E n e r g y s p r e a d - r r ( t o t a l w i d t h ) B u n c h l e r . g t i h a t e x t r a c t i o n R F ° 12 12 12 B a d . e m i t . ( f u l l b e a m ) e n e m n r a d UOw tern liOr V e r t , e m i t ( f u l l b e a m ) ev taaanC ItOn LOT! UOwT a b l e 1 1,0, U-Ar UO, !•• A r . 603 * SSC1 F F h a r m o n i c n u m b e r 1 T 7 RF v o l t a g e kV
Bo
H Ima
N u m b e r o f a c c e l . t u r n s 8 0 6 8 6 8 M a g n e t i c f i e l d s T 1 . 2 2 1 . 5 3 i . l k E x t r a c t e d bears e n e r g y MeV/A 2 . 1 7 3 - k 2 6 . Î Beam r i g i d i t y T . n 2 . 1 2 2 . 6 6 2 . 0 E n e r g y s p r e a d — ( t o t a l w i d t h ) L 1 0 "3 E n e r g y s p r e a d — ( t o t a l w i d t h ) B u n c h l e n g t h ( w i t h p h a s e HF°^
c o m p r e s s i o n , e x t r a c t e d t u r n ) H a d . é t a i t t a n c e £.. a t e j . cunmrad i o n V e r t , o m i t t a n c e e a t e j ." « '
12ïï 5SC2 RF h a r e o n i c n u m b e r 2 2 2 RF v o l t a g e kV75
115 1 5 8Number o f a c c e l . t u r n s
>too
>i»oo ?1*00 M a g n e t i c f i e l d T 1.2U 1 - 3 7 1 . 5 6 E x t r a c t e d beam e n e r g y MeV/A 2 7 - 3 Ul* . 7 9 5 Beam r i g i d i t y T . m 2 . 1 6 2 . 1 . 3 2 . 8 7 E n e r g y s p r e a d -rj- I t o t a l w w i d t h ) 7 1.7 E n e r g y s p r e a d -rj- I t o t a l w w i d t h )R a d . e m i t t a n c e a t e j . Ej{ mmmrad fin V e r t , e m i t t a n c e a t e j . c mmmrad 3T« B u n c h l e n g t h , e x t r a c • t u r n RF° -UI
5EC7CR HMHETIC ntlD (7) .Figure 2 : Basic beats c h a r a c t e r i s t i c s
2.2 Operating r e s u l t s Injector_C0
T e s t s on t h i s c y c l o t r o n began on May 8l . The i n t e r n a l beam i s e a s i l y tuned and t h e a c t u a l e x t r a c t e d bean c h a r a c t e r i s t i c s a r e i n good agreement with com-p u t a t i o n s . Nevertheless t h e f i r s t r e s u l t s concerning t h e d e l i v e r e d beam i n t e n s i t y were lower than expec-t e d . S p e c i a l s expec-t u d i e s on expec-t h i s problem were wade . They showed t h a t t h e v e r t i c a l acceptance of t h e c y c l o -t r o n and -t h e v e r -t i c a l e n i -t -t a n c e of -t h e bean e x -t r a c -t e d fron t h e source were not well enough* natehed.
By changing t h e trim c o i l c u r r e n t c o n f i g u r a t i o n , cyclotron e x t r a c t e d beam i n t e n s i t y haa been gro'-m by a f a c t o r of 5.
Beam l i n e t r a n s f e r LI
- The transparency c o e f f i c i e n t s for a i l t h e GMfIL beam l i n e s and cyclotrons i r e given in t a b l e k. After energy spread minimization (measured a t the image point of t h e low energy spectrometer) tuned by f i n e a c t i o n on i n j e c t o r magnetic f i e l d , t h e t y p i c a l o v e r a l l e f f i c i e n c y for LI i 3 b e t t e r than 8 5 Ï , fllits being po-s i t i o n e d t o l i m i t t h e emittance figure to ho irmmmrad.
- The rebuncher Bl i s t h e sraalieit CANlL's resona t o r . I t works r e a l l y without any problem a t i t s nominal peak v o l t a g e (1J.5 kV).
- Achromatism, c o r r e l a t i o n s , and n a t c h i n g a r e s t i l l nov well c o n t r o l l e d ^ ,
*_§SCJ
The a c c e l e r a t i o n began on June 1982 without phase comp.ession which was a p p l i e d some weeks l a t e r . Magnet
Maximum magnetic f i e l d c o n f i g u r a t i o n has been s u c c e s s f u l l y t e s t e d with Kr " a t f i n a l energy 35 HeV/A needing a f i e l d value Of \.6U t e s l a .
A d r i f t of main magnetic f i e l d (^5 gauss) ia o b served during t h e f i r s t 2 days a f t e r s t a r t i n g , in s p i t e of v e r y g o o d power supply c u r r e n t s t a b i l i t y ( b e t t e r than 10 s) . This e f f e c t i s a cause of d i f f i c u l t i e s for
an easy beam tuning i n the second SSC a t the beginning of every run.
RF_s^stem
Due t o t h e sparking l i m i t of t h e SSC'a r e s o n a t o r s the HF dee v o l t a g e i n i t i a l l y expected cannot be reached except for the upper p a r t of t h e frequency range (above M l MHz). Consequently, for t h e heavier ions (>100 Ainu) we have t o reduce t h e r a d i a l t u r n s e p a r a t i o n a t i n j e c t i o n t o t h e lowest acceptable v a l u e , ( e s p e c i a l l y i n SSC2 where t h e number of t u r n s i s g r e a t e r than fcOO). The t u r n number i n s i d e • both SSC's i s then depending, for a given frequency, on t h e maximum p o s s i b l e value of the RF dee v o l t a g e .
I n j e c t i o n - e j e c t i o n _
Beam i n j e c t i o n and e j e c t i o n a r e performed r o u t i n e l y . A small v e r t i c a l motion ha3 been observed which can be c o r r e c t e d s a t i s f a c t o r i l y . C o r r e l a t i o n s a r e e a s i ly checked a t i n j e c t i o n .
Acceleration_
The f i r s t and l a s t 10 t u r n s a r e pertubed by i n j e c t i o n and e j e c t i o n c i g n e t s . The compensation of t h e s e d e f e c t s i s now achieved with t h e aid of TROPIC code? and a s s o c i a t e d beam c u r r e n t measurements made by means of t h e li s e c t o r yoke probes. The s e c t o r balancing has been then v e r i f i e d : r e s i d u a l bea-s o f f - c e n t e r i n g i s of t h e order of i 5 cm corresponding t o a balancing e r r o r l e s s than ± 2 g a u s s .
The use of phase compression in SSCI l e a d s t o have e r a t h e r s a a l l energy d i s p e r s i o n for t h e e x t r a c t e d bean (AH/H M 0_ 1) .
" Beam_transfer_line_L2
The achromatism i s now i n good agreement with t h e the ore tied c o n d i t i o n s .
Optireun charge r a t i o a t t h e s t r i p p e r i s 3.? c o r r e s ponding t o t h e r a t i o of e j e c t i o n t o i n j e c t i o n r a d i i and t o the r a t i o of a c c e l e r a t i n g frequency harmonic num bers of both SSCs.
The t h i c k n e s s of Carbon s t r i p p e r foils has been op-t i r . i s e d in order op-to geop-t b e op-t op-t e r e f f i c i e n c y ? noop-t only resarOirg t h e s t r i p p e r i t s e l f but with r e s p e c t t o the emittance f i g u r e s before i n j e c t i o n to SSC2. The growth of the energy spread for a beam c r o s s i n g the s t r i p p e r i s order of 1.1 t o 1.5 depending on the i g n i t s energy, and of t h e f o i l t h i c k n e s s .
*_SSC2
t i r s t t e s t s of a c c e l e r a t i o n began in November
198a.
T h e cajciaUB magnetic f i e l d c o n f i g u r a t i o n ( 1,6 t e s l a } has been t e s t e d with t h e a c c e l e r a t i o n of Argon a t 60 HeV/A.
Single t u r n e x t r a c t i o n i s achieved on SSC2 by t h e combined e f f e c t s of a precession of t h e beam c r e a t e d a t i n j e c t i o n and a f i r s t order f i e l d p e r t u r b a t i o n l o c a l i z e d near t h e e x t r a c t i o n r a d i u s .
The same precession i n SSL2 w i l l a l s o be v e i l s u i t e d t o t h e phase connression c o n f i g u r a t i o n . The r e duction of t h e r a d i a l t u r n spacing a t i n j e c t i o n which i s a c o r o l l a r y cf phase compression would r e s u l t in a s u b s t a n t i a l beam l o s s without t h e h e l p of p r e c e s s i o n .
Not enough time was devoted for f i n e t u n i n g of L3 l i n e , t h e achromatism c o n d i t i o n s a r e a c t u a l l y not f u l l y c o n t r o l l e d and matcninghas t o be f r e q u e n t l y retuned depending on the c h a r a c t e r i s t i c s of t h e SSC2 e x t r a c t e d beam.
2 . 3 Beam efficiency.
The o v e r a l l e f f i c i e n c y of GAHIL i s depending on tuning c o n d i t i o n s and of t h e type of p a r t i c l e . Of course t h e e f f i c i e n c y i s g e n e r a l l y b e t t e r , when mea surements a r e made j u s t a f t e r machine r e t i m i n g , t h a n observed i n average during a long time p e r i o d . Table U showo t h e p r a c t i c a l case of Oxygen measured a f t e r bean tuning o p t i m i z a t i o n on November 1983.
Line L SSCI Line L2 SSC2 Lii.e L3, Local ( p a r t . ) X O v e r a l l ( p a r t . ) 1 0 0 B3 83 71 59 7 2b Li2 60 25 95
au"
a-neasi'red fron t h e e j e c t e d beam of t h e i n j e c t o r CO t o monochroaator i c a g e p o i n t .
b - i n c l u d i n g s t r i p p i n g e f f i c i e n c y Table U
With t h e p r e c e s s i o n a l e j e c t i o n i n SSC2 and a f t e r a c o n t r o l of c o r r e l a t i o n s i n L I , the t r a n s p a r e n c y i s now b e t t e r i n SSCI and SSC2 : around 80S i n good a c c e l e r a t i n g c o n d i t i o n s .
2 . 1 Accelerated beams
The t a b l e 5 p r e s e n t s t h e l i s t i n g for a l l ions and e n e r g i e s a l r e a d y f u l l y t e s t e d and a v a i l a b l e with the maximum corresponding i n t e n s i t y on J t a r g e t s .
The naximua bean c u r r e n t s have been measured the machine being p e r f e c t l y t u n e d , the ion source and t h e p u l l T f a r of t h e i r l i f e time l i m i t a .
MAXIMUM EIIERGÏ CURRENT MeV/A p p s enA
° 1. . ,
9 3 . 7 " 1 1.7 1 01 1 1 5 0 0" » « ' / ' .
Ul 1.1 I 01 1 ' 5 0 ^ A r * /1" 2 7 0 . 3 6 1 01 1 80 " A r V " M 3 . 9 1 01 1 1000 " A r V " * 6 0 a . 3 1 01 1 6 0 0 " K r ' / " * 3 ^ . 7 0 . 2 3 1 01 1 100 > ' C a V1 1 6 0 0 . 2 i o1 L •x, 50 x , GAHIL e n e r g y T a b l e 5 : A c c e l e r a t e d b e a m s 3 . GAHIL OPERATIONHo«ever, reduction of t h e energy bprend i s made to the ûetrisient of t h e bean c u r r e n t : a good compro-mise lias t o be found by t h e o p e r a t o r .
The beam along a l l t h e t r a n s f e r bean l i n e s i s driven looking a t beaa p r o f i l e s [MOD for t h e whole ma-c h i n e ) . These d i a g n o s t i ma-c s ma-can be noved in or out and measurements d i s p l a y e d on s c r e e n s .
S t e e r i n g c o r r e c t i o n s being achieved t h e buncher i s switched on. I t s BF v o l t a g e value i a not c r i t i c a l { *\< U5 kV) but i t s HF phase hae t o be c a r e f u l l y tuned watching t h e beam c e n t r a l phase a t the end of LI. The r i g h t RF phase i s obtained when t h e beam c e n t r a l phase does not change with or without buncher on.
* SSCI
During t h e f i r s t few months of o p e r a t i o n , most equipments were i n d i v i d u a l l y s e t up and tuned by means of t h e 16 pseudo-knobs a s s o c i a t e d with k touch p a n e l s . Moreover numerous b a s i c equip ments such as HF systems, RF" phase adjustement 3ystem and a c e r t a i n num-ber of s t e e r i n g power s u p p l i e s were not connected t o t h e main computer.
After a year of completion, t h e computer c o n t r o l system i s now linked to 1500 equipments or parameters and o f f e r s the expected f a c i l i t i e s .
With t h e fast development of s p e c i f i c user s o f t -ware {or t a s k s ) for t h e machine o p e r a t i o n , i t became t h e powerful and e f f i c i e n t t o o l for people in charge of beam t u n i n g and surveying.
* I n i t i a l _ s e t t i n g s
Approximately 6 hours are now necessary for t h i s o p e r a t i o n . The power s u p p l i e s (about 220 r e g u l a t e d c u r -r e n t powe-r s u p p l i e s , t h o s e of the expe-rimental i -r e a s not s t i l l included) a r e a u t o m a t i c a l l y switched on and s e t t o the expected v a l u e with d i f f e r e n t u s e r t a s k s , t a k i n g the values in t h e computer d i s k - f i l e .
SSC's magnetic f i e l d s a r e p r e c i s e l y c y c l e d , t h e i r power s u p p l i e s being under a d e d i c a t e d micropro-c e s s o r , while t h e o t h e r s d i p o l e s , sumicropro-ch as bending mag-n e t s i mag-n beam l i mag-n e s , a r e cycled d i r e c t l y by t h e oaimag-n computer.
Balancing of t h e SSC's sector, i s done by means of a combined a c t i o n of t h e main ccuputer and of a l o c a l automatic gaussneter using f o r each SSC U NMH probes a t t h e c e n t e r s of t h e s e c t o r s .
The RF parameters are c o n t r o l l e d by 5 l o c a l micro-p r o c e s s o r s (one micro-per c y c l o t r o n , one for t h e buncher and one for RF phase adjustment) which are under the main c c a p u t e r dependence^1",
The PIC source being .-witched on t h e i n j e c t o r cy-c l o t r o n i s e a s i l y tuned. Attention must be paid t o have a good beam matching i n t h e t r a n s f e r l i n e LI : the energy spread of the CO beam must be c a r e f u l l y mini-mized by means of small c o r r e c t i o n s on t h e main ma-g n e t i c f i e l d .
All t h e previous magnetic and RF parameters being put on, a p r e l i m i n a r y RF phase v a l u e for t h e RF r e s o n a t o r s i s computed, using c e n t r a l beam phase probes ( a b s o l u t e measurement method)1!1*.
Then t h e o p e r a t o r uses s e v e r a l o t h e r t a s k s t o tune r e a d i l y t h e beam following t h e normal procedure :
- t o a l i g n t h e beam on t o t h e i n j e c t i o n channel a x i s ,
- t o find t h e optimal r a d i a l phase law, ' t o determine t h e b e s t i n j e c t i o n phase looking a t t h e s e p a r a t i o n of t h e l a s t h t
tuning t h e RF phase,
c e l e r a t e d t u r n s and
t o put t h e beam in t h e c e n t e r of the f i r s t e j e c -t i o n e l e c -t r o s -t a -t i c sep-tum.
All t h e s e o p e r a t i o n s are now made with the very convenient a i d of numerous s p e c i f i c codes or t a s k s on wich d e t a i l e d informations a r e given i n other papers ( t h i s c o n f e r e n c e ^ , 9 ,
I f t h e above mentionned procedure i s c a r e f u l l y Tollowed then t h e si.igle turn e x t r a c t i o n i s s t r a i g h t forward with a good e f f i c i e n c y ( ^ O î ) .
» Transfer l i n e L2
The focusing parameters a r e known b e t t e r than in LI and t h e t h e o r i c a l conditions ( p a r t i c u l a r l y achromatism and matching) a r e r a t h e r well c o n t r o l l e d .
Then t h e tuning only consist bending adjustments.
1 SSC2 and L3
The procedure i n use i s e x a c t l y t h e Bone as Cor SSC1. However i t i s not p o s s i b l e t o assume a fixed number of t u r n s l i k e in SSCI , t u r n s being not, s e -p a r a t e d a t e j e c t i o n . Consequently t h e tuning of t h e l i n e L3 s t r o n g l y depends on the c h a r a c t e r i s t i c s of t h e e x t r a c t e d beam : t h e o r i e n t a t i o n and t h e ehape of t r a n s v e r s e emittance may change with a. change in t h e tuning of SSC2.
From t h i s , i t r e s u l t s a p r a c t i c a l d i f f i c u l t y when the machine i s working for physics : complete retiming of L3 and experiments beam l i n e i s a n e c e s s i t y i f f a i l u r e s or breakdowns o c c u r , changing the a c -c e l e r a t i n g -c o n d i t i o n in SSC2.
3.2 Operation statistics and experiences
In normal operation lfl days run (trio m o d e ) are followed by a maintenance week.(5k shift r u n ) .
The run is usually divided in starting time (36 h o u r s ) , machine studies (US h o u r s ) , new beam tests (72 hours) and physics (276 h o u r s ) .
During the first year of operation ( 1933 ) , the beam time devoted to physicists has been 62Ï of GANIL's Tacility running time. Table 6 gives the distribution of the running time (l?83t.
Scheduled {hour3) Actual {hours)
2 H 6 63 385 336 765 Physics t i n -P a r t i c l e changes liew bean developaents Machine s t u d i e s s t a r t i n g time S296 56 370 569 765 Actual {hours) 2 H 6 63 385 336 765 Total running t i n e L056 1*056 Table 6
Table 7 and F i g . 3 represent the physics time dis'
Bean on t a r g e t time Povn time (tunïng+breakdowr^ Running maintenance Total physics time
hours X Bean on t a r g e t time
Povn time (tunïng+breakdowr^ Running maintenance Total physics time
1260 1000 165 53 111 7 100
Table 7 : Physics time distribution on '
HOURS
zsoJ
gBRCAKDaWH iHSTIWIHB. g BUNKING KAMENAHCE. ]j]AVlUUBL£ BEAM.
HiTHT
«TUM. «MUBIUT7Short i n s t a b i l i t i e s of t h e 50 Hz mains f r e q u e n t l y lead us t o a f u l l r e - s e t t i n g up t h e machine parameters and r e p r e s e n t an important u n a v a i l a b l e beam t i m e . Conse q u e n t l y , a program of implementing changes t o t h e e x i s -t i n g power s u p p l i e s has been r e a l i s e d and a 120 kVA , i n v e r t e r i n s t a l l e d t o save computers and e l e c t r o n i c s . !
At t h e beginning the long term d r i f t of a few p a r a -meters r e s u l t e d in hours of retuning but with experience and improvements l i k e beam feedback c o n t r o l s , t h e l o s t time has been reduced by a f a c t o r two, while t h e time f a i l u r e s r a t i o decreased t o about 8K of t h e t o t a l experiment t i m e ,
3.3 Operation s t a f f
The t h r e e c y c l o t r o n s and the beam l i n e s a r e r o u -t i n e l y d r i v e n by 3 o p e r a -t o r s , p a r -t i a l l y backed up by one o p e r a t i o n e n g i n e e r (2 s h i f t s a d a y ) . 3 . ^ Ion source maintenance
. L i f e of PIG sources depends on t h e kind of a c c e l e r a t e d p a r t i c l e and on expected bean i n t e n s i t y . Mean values a r e s u a a a r i z e d in t a b l e 8. h o u r . h o u r a 21. 30 A r!* 21 16 K r7* K rB* l!4 t t 0 ' * 21. 30 Table 8
It. HACUIHE STUDIES
Machine s t u d i e s performed on GAMIL have included s t u d i e s on SSC's and on beam t r a n s p o r t l i n e s . Beam t r a n s p o r t l i n e s a r e t r e a t e d i n a separated' paper uhere a r e described t h e problems of b e t a t r o n and chromatic matching from l i n e s t o SSC's and from SSC's t o l i n e s . ' SSC's s t u d i e s can be put i n t o tvo c l a s s e s , ignoring t h e a c t u a l c h r o n o l o g i c a l order i n which they were
.1 Transverse motion i n SSC's
, 2
The four probes method p r e v i o u s l y d e s c r i b e d in allows not only t h e observation of b e t a t r o n o s c i l l a -t i o n s bu-t a l s o -t h e measuremen-t of c l o s e d o r b i -t off-c e n t e r i n g . F i e l d unequalitieB i n t h e four s e off-c t o r s off-can .be d e t e c t e d and c o r r e c t e d . The effect of r e s i d u a l
f i e l d l o c a l imperfections can be compared t o o r b i t com-p u t a t i o n s ' . F i g . u 3hows an examcom-ple on SSC2 f i r s t 80 t u r n 3 . Such a good r e s u l t encouraged an extensive use of computer simulation t o study a p r o c e s s i o n a l e x t r a c -t i o n wi-th bump. Af-ter abou-t -t(60 -t u r n s a p r e c e s s i o n of 15 t o 20 mm (35 mm peak t o peak) and a small amount of bump, good i n s i m u l a t i o n , gave e x p e r i c e n t a l l y an e x c e l l e n t t u r n secar'tion, F i « . 5 allowing a. p r a c t i c a l l y l o s s l e s s e x t r a c t i o n . 5nr~.)
/^\
v.-MEASURED / COMPUTED 5nr~.)/^\ v.-
S'^Stf/ "^
~C/
/ / V s . ED COI 'I
F i g . 5a : SSC2 l a s t t u r n s (Buap p e n c i l bean)
Bunch l e n g t h compression from f i e l d p e r t u r b a t i o n i s used i n CAHIL S S C l 1 0 . i l. T h e moat e vi d e n t observa
t i o n of t h e e f f e c t i v e n e s s of t h e method has been ob t a i n e d from d i r e c t bunch measurement(Fig. 6) on t h e beam p r o b e .
f i g . ?b : ESC2 le.st t u r n s (Bucp + p r e c e s s i o n ) 1).? Longitudinal motion in SSC's
On t h i s complex problem, s t u d i e s mainly concerned !:•' adjustment (or e f f e c t of misadjustments ) of r f v o l t a g e , rf phase and magnetic f i e l d of SSCI.
A change i n r f v o l t a g e V p r a c t i c a l l y only changes the f i n a l energy j i t provides an e x c e l l e n t method for a d j u s t i n g t h e chromatic matching of a SSC i n t o i t s output t r a n s p o r t l i n e 5 .
Optimization of r f a c c e l e r a t i n g phase 4 _ can be made according t o s e v e r a l c r i t e r i a : maximum energy, minimum energy s p r e a d , minimum bunch l e n g t h a t some given p o i n t . Even i . ' t h e l a s t method i s probably going t o be p r e f e r r e d i n t h e f u t u r e t h e f i r s t two have so f a r been mere examined, e i t h e r by looking a t t h e l a s t t u r n s i n s i d e t h e SSC or by using t h e monochromator.
GANIL SSC's r f c a v i t i e s a r e d e l t a shaped and each g a p , in a d d i t i o n t o a c c e l e r a t i o n , produces a t r a n s v e r s e k i c k . For peak a c c e l e r a t i o n phase, the two kicks of a d e l t a cancel each o t h e r ; not f o r o t h e r phases, Mith tvo c a v i t i e s per t u r n t h e e f f e c t of such kicks i s r e duced, but not completely j in p a r t i c u l a r t h i s i s t r u t for the f i r a t turn «here the i n j e c t i o n o r b i t c r o s s e s t h e f i r s t c a v i t y with a d i f f e r e n t phase. As observed experimentally t h e r e s u l t i s t h e e x c i t a t i o n of a b e t a t r o n o s c i l l a t i o n with an amplitude p r o p o r t i o n a l to input phase displacement : according t o t h e t u r n and t h e azimuth on which t h e r a d i u s i s observed f o r phase o p t i m i z a t i o n , 3everal degrees e r r o r may r e s u l t from t h i s e f f e c t . A vay t o avoid such an e r r o r i s t o choose for the o b s e r v a t i o n a node of t h i s b e t a t r o n o s c i l l a t i o n
I f , s i m i l a r l y , t h e e x t r a c t i o n e l e c t r o s t a t i c s e p t u s i s put at such a node, j u s t a small change i n v o l t a g e , «hen c l o s e t o optimum phase, i s enough t o keep the beam t r a j e c t o r y fixed in Lhe uutyut t r a n s p o r t channel when t h e i n j e c t i o n phase i s being a d j u s t e d .
I f compression i s e a s i l y achieved, f i e l d a d j u s t a e n t and phase l a v oay however r e q u i r e some c a r e and a s p e c i a l c h o i c e . In p a r t i c u l a r a change i n average f i e l d i s then changing l i n e a r l y t h e energy : only about one gauss i n c r e a s e i s enough t o i n c r e a s e t h e energy by s e - . v e r a l per cent and change t h e e x t r a c t i o n t u r n . A study of t h i s phenoaenon1^ has shown t h a t one vay t o avoid
t h i s e f f e c t i a to i n c r e a s e t h e average f i e l d and adopt a phase law as i n d i c a t e d on F i g . 7b(such a law uould i n f a c t avoid i n t h e same time the r i s k of r a d i a l emittance i n c r e a s e in case of r e l a t i v i s t i c o p e r a t i o n1^ .
Experimentally, t h e f i e l d l e v e l producing t h i 3 phase law can e a s i l y be found with t h e h e l p of t h e monochro-mator by p r o g r e s s i v e l y i n c r e a s i n g and r e s j u s t i n g continuously V and $ i n order t o keep the same e x t r a c t e d t u r n and optimize t h e energy spread (with a proper number of t u r n n - a e e above-a s l i g h t c o r r e c t i o n of e l e c t r o s t a t i c e x t r a c t o r v o l t a g e i s s u f f i c i e n t t o keep t h e beam p e r f e c t l y a l i g n e d in t h e t r a n s p o r t l i n e ) . For a proper B f i e l d l e v e l one has 3H /3B = 0 for t h e optimum phase and v o l t a g e adjustment.
Z.Q RAPJIU (n>) Fig. 7a i_KorcBl phase l a v
- J i . n
RABIW (m)
The time s h a r i n g between two experiments i e a l -ready o p e r a t i o n a l . , but t h e beam i n t e n s i t y should a l s o be c o n t r o l l e d according t o t h e u s e r ^ demand. This w i l l be posoible in t h e next future by the means of a s l i t of s p e c i a l design which w i l l be synchronized v i t h t h e beim conunutntion.
5.2 On-line beam s t a b i l i s a t i o n
Owing t o t h e great s e n s i t i v i t y of t h e beam phase t o the v a r i o u s p a r a m e t e r s , s e v e r a l feedback c o n t r o l systems have been designed using o n - l i n e beam measure-ments as shown i n F i g . 8. The b a s i c p r i n c i p l e i s t o keep c o n s t a n t t h e beam c e n t r a l phase a l l along the machine by a d j u s t i n g the i n j e c t o r RF v o l t a g e , t h e main magnetic f i e l d of SSCI , the p o l a r i s a t i o n of t h e s t r i p -per and the main magnetic f i e l d of SSC2.
~ 35m ~ 4 D m I ^ 1 5 m
I ~20m
Buncher Strippern ——[sïl——JssciU
ifi"
[VST 1—y wr
F i g . 8 5.3 SSC's magnetic f i e l d adjustmentThe f i e l d l e v e l and t h e balance of t h e four magnet s e c t o r s of each SSC are adjusted using four Hall probes movable along the s e c t o r a x i a . At t h e beginning the a c -curacy of th<: Hall gaussmeter system was about i 1 g a u s s , but during a year of experience v« have o b -served d r i f t s in t h e a b s o l u t e c a l i b r a t i o n of Hall p r o b e s .
As t h e r e c a l i b r a t i o n i s a. c r i t i c a l o p e r a t i o n due t o t h e t i g h t n e s s of the system involved i n t h e SSC design and t h a t we would l i k e a b e t t e r accuracy on f i e l d l e v e l measurement we have decided t o i n s t a l l KMR probes j l o s e t o Hall probes, When t h e isochronism f i e l d g r a d i e n t i s s u f f i c i e n t l y Bmooth we can uae d i r e c t l y NMH probes t o adjust the f i e l d within ± l . 1 0- s otherwise
r e c a l i b r a t i o n of Hall probes i s done j u s t before p u t -t i n g in f i e l d g r a d i e n -t .
For o n - l i n e c o r r e c t i o n s , HMH compensated g r a d i e n t probes has been i n s t a l l e d a t t h e r e a r of t h e pole gap (one per S5C). This main magnetic f i e l d measurement w i l l allow permanent monitoring and o n - l i n e feedback c o r r e c t i o n of t h e s t a r t i n g d r i f t .
5.1* Second i n j e c t o r and ZZB source
In a d d i t i o n t o t h e i n t e r n a l s o u r c e , an £CR source HIKIHAFIOS, a c t u a l l y in t e a t a t GREKOBLE (R. C e l l e r ) w i l l be incorporated i n t h e 2nd i n j e c t o r . An i n j e c t i o n system has been designed and i t i s under c o n s t r u c t i o n . The a x i a l i n j e c t i o n o p e r a t i o n i s expected in June 9 5 ' 5 . 5.5 Ion sources
The design of GA'.'IL has been based upon the c h a r a c -t e r i s -t i c s cf -t h e PIC ion s o u r c e . îîew -types of ion sources a r e i n t e r e s t i n g as far as they y i e l d beams of
s i m i l a r charge stateB i n s u f f i c i e n t abundance. This i s the case of t h e ECR s o u r c e , as f a r as gaseous ions a r e concerned. The production of m e t a l l i c ions i s t o be developped in t h e next f u t u r e for t h i s type of source whose main advantage i s on almost con-tinuous o p e r a t i o n .
g.T Time s t r u c t u r e
Various demands have been formulated by t h e u s e r s concerning time s t r u c t u r e of t h e beam. The r-OBt d i f f i c u l t requirement i s r e l a t i v e t o t h e production of very s h o r t pulses , i n t h e order of .2 nanosecond.. At t h e p r e s e n t t i m e , with s p e c i a l c a r e , p u l s e s , a l i t t l e smaller than one nanosecond can be produced. More machine s t u d i e s have s t i l l t o be made so aa t o find t h e most convenient s o l u t i o n .
6. PHÏSICS EXPERIMENTS AMD FUTURE BEAMS
During t h e f i r s t 15 month3 of o p e r a t i o n , phys i c phys a t GAHIL waphys c a r r i e d out eaBftntially along 2 d i -r e c t i o n s .
- Reaction mechanism - Production of e x o t i c n u c l e i
The main p o i n t s of i n t e r e s t which have shown up during t h e s e s t u d i e s a r e :
Ï - S l a s t i ç _ s e a t t e r i n g (27 and kk HeV/A *• 9Ar + Ni,
Sn and PbT.
The r o l e s of t h e r e a l and t h e imaginary p a r t s of t h e o p t i c a l p o t e n t i a l can c l e a r l y be disentangled. A Coulcnb rainbow and a l<0! reduction of t h e depth of t h e r e a l p o t e n t i a l a r e observed. There r e s u l t s are c o n s i s -t e n -t wi-th -t h e 86 HeV/A, 1ZÇ, CERTÎ d a t a .
*_ Mi £2_£D£rfiL 5 Î I HE ï "££5 _î £LS G *• r K ~ 2E£ ^£ £2 (*iU MeV/A "aA r + 2 0 BP b ) : a r e ? -.11 present a t such an
higher i n c i d e n t energy.
*_^22ï_2l2GJi!E2duction_(ljI* HeV/A "°Ar + Ca, Sn, U) : c r o s s - s e c t i o n s betveen 1 and j pb have been mea-s u r e d , with t h e dame A1 / ] dependence, v e i l below t h e
t h r e s h o l d .
î_guBsi-fusign_eyents_are_obBerved (a? MeV/A
''"Ar + " C , I 7A 1 and Ag) with 35 HeV/A 1 5K r i o n s , a
good evidence for f i s s i o n e v e n t s and v e r y Btrongly r e l a x e d products i s o b t a i n e d from t h e same t a r g e t s . *..?E!K2££E_S£_li25S£_525§2£!iE (27 and Uh HeV/A "0Ar or 1 , 7A r , I 3* T h and Ï J ,U ) : a l a r g e amount of masa
appears t o be t r a n s f e r r e d t o t h e t a r g e t . E x c i t a t i o n e n e r g i e s as l a r g e as 900 MeV could be deposited in a quasi compound nucleus system. A l a r g e degree of r e l a -x a t i o n s ie reached, Kowç v e r , t h e q u a l i t a t i v e p a t t e r n s are s t r o n g l y d i f f e r e n t a t 27 and Mi HeV/A.
As for t h e production of e x o t i c n u c l e i , 3 main e x -perimental s e t - u p ore used.
"_ySËS_5E££5£2E££ëI : a l c a l i n e (Rb) and halogeneoua
(Br, I ) d i s t r i b u t i o n have been obtained with 100 HeV/A
1 60 and III* HeV/A ° A r .
!Lû3_!!êIjiS5_ïï!225£2lt_§ïlïS2 i-3 aov u n |ie r o p e r a t i o n .
^_ÎËÊ_5ïESÎl2î£ÎBBSâ_i£2_iinf_^iii§iL> i n c l u d i n g
Hopefully, p h y s i c a l r e s u l t s a r e to fee expected during the second h a l f of 1981».
Future_beams_
The f u t u r e new ions having t o be t e s t e d a r e sum marized i n t a b l e 9 P a r t i c l e Energy KeV/A Hot s t i l l scheduled " B e " S i ,2S 95 Hot s t i l l scheduled "°Ti ^ 2 Hot s t i l l scheduled " N i 55 Tested i n i n j e c t o r + L1 , uK r »*5 Hot s t i l l scheduled "!X e " " * 23 Will be t e s t e d an Hay fll T-ble 9 COHCLUSIOH
- After a f i r s t year of completion, the beam cha r a c t e r i s t i c s have been a p p r e c i a b l y improved : t h e beam i n t e n s i t y from the i n j e c t o r has been grown by a f a c t o r of 5 and t h e o v e r a l l machine transparency by roughly a f a c t o r 3. The beara o p t i c a l q u a l i t y , s t a b i l i t y aad r e -produc i b i l i t y a r e ncv b e t t e r c o n t r o l l e d . In t h e same time t h e a v a i l a b i l i t y of beams for phyaica reached i n average 70* of the scheduled time,
- These encouraging r e s u l t s a r e t h e consequence of t h e time a l l o t e d for machine s t u d i e s , but would have not been p o s s i b l e without t h e enthusiasm of CABIL peoples
- Hith the next i n s t a l l a t i o n of t h e ECR ion s o u r c e , we hope for new a p p r e c i a b l e improvements i n the beam s t a b i l i t y and a v a i l a b i l i t y .
REFERENCES
1. J . Fermé e t a l . "StatU3 r e p o r t on GAIIIL" 9 t h I n t . Ccnf. cn Cyc. and t h e i r Appl. CAEN - 1901 - France 2. GASIL Group " S t a t u s r e p o r t on GASIL" P a r t . Accel.
Conf. SANTA FEE - 1983 - US
3 . A. Chabert e t a l . " S t a t u s r e p o r t on GMIL" Proc. or t h e 8th A l l Union P a r t . Accel. Conf. PROTVItIO -1982 - URSS.
It, H.P. Bourgarel e t a l , "Progress r e p o r t and f i r s t Operation cf t h e GAI.'IL I n j e c t o r 9 t h I n t , Conf. on Cycl. and t h e i r Appl. CAEN - '981 - France.
5 . R. Beck e t a l . "Beara Transmission Efficiency between I n j e c t o r and Target i n t h e CANIL Complex t h i s Conf.
6. H. Proné e t a l . "The Operation of t h e GAHIL Control System, t h i s Conf.
T. C. Bieth et a l . "GANIL RF Systems : C a v i t i e s T r a n s m i t t e r s and Coupling System" 9 t h I n t . Conf. on Cycl. and t h e i r Appl. CAEN - 1981 - France.
8. A. Joubert e t a l . "Main r é s u l t a on t h e RF Amplitude and Phase Regulation Systems i n Operation a t GAHIL t h i s Couf.
9. GABIL Croup "GAHIL Beam S e t t i n g Methods Using on Line Computer Codes" P r o c . of t h e Conf. "Computing in Accelerator Design and Operation" BERLIN WEST -1983 - RFA.
10. A. Chabert e t a l . "Bunch length Compression i n s i d e • a Separated Sector Isochronous Cyclotron and Related Problems'.' - " P a r t i c l e A c c e l e r a t o r s Conf." WASHINGTON - 1981 - USA.
11. P. L a p a a t o l l e "Hew Heavy ion A c c e l e r a t o r s " P a r t . Accel. Conf. SANTA FEE - 1983 - US.
12. P. LapoBtolle "Réglage de l a Phase, de l a Tension A c c é l é r a t r i c e e t du Champ Magnétique d'un CSS en Régime non I s o c h r o n e " . GANIL 83R/O2T/TP/01. 13. P. L a p o s t o l l e "Recent Developments on Beam Dynamics;
in C y c l o t r o n s " 9 t h I n t . Conf. on Cycl. and t h e i r
Appl. CAEN - 1981 - F r a n c e .
lit. A. Chabert "Beae Tuning and S t a b i l i z a t i o n * U s i n g Bean Phase Measurements a t GAHIL" t h i s Conf. 15- H.P. Bourgarel "GAML Axial I n j e c t i o n Design with
