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THE NUCLEAR STRUCTURE FACILITY TANDEM
AT DARESBURY LABORATORY
R. Voss
To cite this version:
JOURNAL DE PHYSIQUE Colloque 0,5, supplément au n° 11, Tome 37, Novembre 1976., page C5-223
THE NUCLEAR STRUCTURE FACILITY TANDEM AT DARESBURY LABORATORY
R. G. P. Voss
Daresbury Laboratory, Science Research Council, Daresbury, Warrington WA4 4AD, England
Résumé. — Un accélérateur électrostatique tandem pour ions de toutes sortes, y compris les ions lourds, et en construction au Laboratoire de Daresbury. Le projet est bien avancé, et un effort considérable continue d'être consacré à un programme de recherche et développement dans la technologie des accélérateurs électrostatiques.
Abstract. — A 30 MV tandem electrostatic accelerator for ions of all types, including heavy ions, is being built at Daresbury Laboratory. Construction is well advanced, and considerable effort is continuing to be devoted to an R & D programme into the technology of electrostatic accelerators.
As far back as the 1960's British universities be-gan discussing plans for a major new accelerator for nuclear structure research. This culminated in a proposal for a large tandem accelerator, with a ter-minal potential in excess of 20 MV. The Science Re-search Council took the next step in carrying out a detailed feasibility and design study at the Dares-bury LaboratoryCl]. Financial approval was obtained and construction was started at Daresbury in 1974.
Daresbury Laboratory is situated in the north-west of England, about 300 km from London, and roughly midway between Liverpool and Manchester.
The tandem is designed to commence operation at 20 MV on terminal and to be capable of upgrading to 30 MV. It will accelerate all ions from hydrogen to uranium, and the design incorporates provision for polarised and pulsed beams[2]. Figure 1 shows the plan layout of the building. The tandem is vertical,
Fig.l. — Plan view of building.
R.G.P. VOSS
Fig.3. - D e t a i l of s t a c k
Fig.2. - Cutaway view of a c c e l e r a t o r .
and beams a r e b e n t by a 90' double-focusing s p e c t r o - meter i n t o any one of t h r e e s h i e l d e d e x p e r i m e n t a l
a r e a s . C o n t r o l and c o u n t i n g a r e a s , and p l a n t asso- c i a t e d w i t h t h e a c c e l e r a t o r and e x p e r i m e n t a l equip- ment, a r e housed i n t h e l a b o r a t o r y b l o c k on t h e l e f t of t h e diagram. The b u i l d i n g h a s been d e s i g n e d , and s i t e d w i t h r e s p e c t t o land c o n t o u r s and t h e o t h e r b u i l d i n g s on t h e s i t e , i n an a t t e m p t t o l e a v e maxi- mum f l e x i b i l i t y f o r f u t u r e expansion, such a s long beam l i n e s f o r t i m e - o f - f l i g h t experiments o r t h e ad- d i t i o n of a second a c c e l e r a t o r .
F i g u r e 2 shows a cutaway of t h e a c c e l e r a t o r . The main tower and t h e a d j a c e n t s e r v i c e tower a r e com- p l e t e , and t h e i n j e c t i o n room i s a t p r e s e n t under c o n s t r u c t i o n . The o v e r a l l h e i g h t i s 70 m. The p r e s - s u r e v e s s e l , 45 m i n h e i g h t and 8.2 m i n d i a m e t e r , h a s been f a b r i c a t e d i n s i d e t h e tower and h y d r a u l i c - a l l y t e s t e d . A t t h e o p e r a t i n g p r e s s u r e of 0.75 MPa i t w i l l c o n t a i n about 140 t of p u r e SF6.
Focusing of t h e beam w i t h i n t h e a c c e l e r a t o r i s by f o u r s e t s of magnetic q u a d r u p o l e - t r i p l e t s . An o f f - s e t quadrupole t r i p l e t 'in t h e c e n t r e t e r m i n a l pro- v i d e s charge s t a t e s e p a r a t i o n a f t e r t h e f i r s t s t r i p - p e r , and h a s been t e s t e d i n a heavy i o n beamC31. An
i n t e r s h i e l d i s used t o e n a b l e h i g h t e r m i n a l poten- t i a l s t o b e achieved w h i l e r e t a i n i n g a r e l a t i v e l y s m a l l p r e s s u r e v e s s e l diameter.
D e t a i l s of t h e column a r e shown i n f i g u r e 3. The i n s u l a t o r l e g s a r e made of g l a s s d i s c s glued between s t a i n l e s s s t e e l e l e c t r o d e s formed t o p r o v i d e a n n u l a r s p a r k gapsC47. Manufacture of t h e s e i n t h e l a b o r a - t o r y i s w e l l advanced. Charging i s by means of a laddertronC51. Power i s t r a n s m i t t e d t o a l t e r n a t o r s i n t h e dead s e c t i o n s and t h e c e n t r e t e r m i n a l by a r o t a t i n g s h a f t . Most i t e m s f o r t h e c o l u ~ a r e a l - ready on s i t e . The beam t u b e i s s i t u a t e d c e n t r a l l y and i s graded by a s e p a r a t e r e s i s t o r c h a i n .
TANDEM AT DARESBURY LABORATORY
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Fig.5.
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L i g h t l i n k system.tem i s a t an advanced s t a t e . E l a b o r a t e measures have shown i n f i g u r e 5.
been t a k e n t o p r o t e c t t h e c o n t r o l system w i t h i n t h e Because of t h e many u n c e r t a i n t i e s i n t h e s c i e n t i - a c c e l e r a t o r from t h e e f f e c t of s u r g e s . To reduce t h e f i c and t e c h n i c a l i n f o r m a t i o n on how e l e c t r o s t a t i c e f f e c t of any f a i l u r e , t h r e e s e p a r a t e l i g h t l i n k a c c e l e r a t o r s o p e r a t e , o r f a i l t o o p e r a t e , t h e Labor- systems a r e i n c o r p o r a t e d i n t h e a c c e l e r a t o r , a s a t o r y h a s maintained a s u b s t a n t i a l r e s e a r c h and de-
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F i g . 6. - P i l o t machine.
velopment prograrmne s i n c e t h e d e s i g n s t u d y s t a g e . Equipment which h a s been developed f o r t h i s purpose i n c l u d e s a 1.5 MV single-ended Van de G r a a f f , a 1 MV
Marx p u l s e generatorC71, methods f o r measuring t h e s u r g e s a c r o s s i n d i v i d u a l components under t e s t v o l t - ages.181, and a 10 MV single-ended e l e c t r o s t a t i c ac- c e l e r a t o r . The l a t t e r i s known a s t h e p i l o t machine, b e i n g c o n s t r u c t e d of t h e components a s designed f o r t h e main a c c e l e r a t o r . I t s column l e n g t h i s 3 m. It
i s shown i n f i g u r e 6.
The programme c a r r i e d o u t on t h e s e f a c i l i t i e s h a s covered t h e d e s i g n and t e s t i n g of components such a s r e s i s t o r s and r e s i s t o r p r o t e c t i o n , i n s u l a t o r mater- i a l s , s p a r k gaps, l a d d e r t r o n r i n g s and i n s u l a t o r s , p r o t e c t i v e c i r c u i t s f o r e l e c t r o n i c s systems. Com-
p l e t e systems can b e thoroughly t e s t e d i n t h e p i l o t machine, e.g. t h e l a d d e r t r o n charging system and t h e power t r a n s m i s s i o n system. The c o n t r o l system of t h e p i l o t machine i s based on t h e components developed f o r t h e main system: computer w i t h f l o p p y d i s c , c o l - our TV d i s p l a y , and modulated l i g h t - l i n k . A l l t h e s e systems have been o p e r a t e d f o r many hundreds of hours w i t h t h e machine running a t p o t e n t i a l s i n t h e range 8 MV t o 10 MV, w i t h a number of tank s p a r k s b e i n g induced every hour. T h i s i s a t p r e s e n t t h e most r i g o r o u s regime a v a i l a b l e f o r t h e t e s t i n g of components under s e v e r e h i g h v o l t a g e breakdown con- d i t i o n s .
The q u e s t i o n of t u b e development i s a s u b j e c t i n i t s own r i g h t . One of t h e fundamental d e c i s i o n s tak- e n i n t h e e a r l y s t a g e s of t h e p r o j e c t was t o a v o i d a t u b e c o n t a i n i n g o r g a n i c m a t e r i a l . To t h i s enr: t h e L a b o r a t o r y h a s developed a tube based on bonding ceramic i n s u l a t o r s d i r e c t l y t o a t i t a n i u m a l l o y . It
t u r n s o u t t h a t w h i l e g l a s s i s p r e f e r a b l e a s t h e col- umn i n s u l a t i n g m a t e r i a l , h i g h d e n s i t y alumina i s more s a t i s f a c t o r y a s a t u b e i n s u l a t o r . E x t e n s i v e t e s t s have been done on s i n g l e gap s e c t i o n s , on mul- t i p l e gap u n i t s , on e l e c t r o d e m a t e r i a l s by them- s e l v e s , and on long i n s u l a t o r s e c t i o n s , i n o r d e r t o a t t e m p t t o i s o l a t e t h e f a c t o r s r e l a t i n g t o i n s u l a - t o r s u r f a c e , e l e c t r o d e m a t e r i a l s and f i n i s h , and t h e e f f e c t s of e l e c t r i c f i e l d , p o t e n t i a l d i f f e r e n c e , and vacuum i n t h e t u b e . C o n s i d e r a b l e a t t e n t i o n h a s been p a i d t o t h e s h a p i n g of t h e e l e c t r i c f i e l d i n t h e tube and i t s i n f l u e n c e on t h e t r a j e c t o r i e s of secondary p a r t i c l e s . A p r o t o t y p e t u b e of u n i t modu- l a r l e n g t h ( a b o u t 750 mm) was t e s t e d i n t h e p i l o t machine, and o p e r a t e d r e a s o n a b l y s a t i s f a c t o r i l y up t o t h e d e s i g n g r a d i e n t of 2.2 MV/m. The l e s s o n s l e a r n t from t h i s a r e i n c o r p o r a t e d i n an improved t u b e now b e i n g assembled f o r t e s t .
It i s a n t i c i p a t e d t h a t tube development w i l l con- t i n u e t o form an important p a r t of t h e L a b o r a t o r y ' s R & D programme f o r some c o n s i d e r a b l e time.
References
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Design Study f o r ' a Nuclear S t r u c t u r e F a c i l i t y C51 AITKEN, T.W. and CHARLESWORTH, T.R., Daresbury a t Daresbury, Daresbury L a b o r a t o r y R e p o r t , L a b o r a t o r y I n t e r n a l Report, DL/NSF/TM 1 3 (1975). DNPL/NSF/R 4 (1973).C21 AITKEN, T.W. e t a l .
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I n s t r . Meth.122
C61 HORRABIN, C.W., e t a l . Daresbury Laboratory(1974) 235. Report, DL/NSF/R 1 3 (1975).
L31
EASTHAM, D.A. e t a l .Nucl.
Instr. Meth.177
C71 CHARLESWORTH, T.R., and HALLIDAY, B.S., Daresbury(1974) 495. L a b o r a t o r y I n t e r n a l Report, DL/NSF/TM 17 (1976).
C41 AITKEN, T.W. and CHARLESWORTH, T.R., Daresbuxy
