THE HOLIFIELD HEAVY-ION RESEARCH FACILITY AT OAK RIDGE

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THE HOLIFIELD HEAVY-ION RESEARCH

FACILITY AT OAK RIDGE

J. Ball, J. Martin, J. Biggerstaff, C. Jones, R. Lord, R. Robinson, F. Plasil

To cite this version:

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JOURNAL DE PHYSIQUE Colloque C5,, supplément au n° \\, Tome 37., Novembre 1*376,, page C5-227

THE HOLIFIELD HEAVY-ION RESEARCH FACILITY AT OAK RIDGE J. B. Ball, J. A. Martin, J. A., Biggerstaff, C M . Jones,

R. S. Lord and R. L. Robinson (Paper presented by F. Plasil)

Oak Ridge National Laboratory,* Oak Ridge, Tennessee 37830, USA

Abstract. This paper describes the new accelerator facility under construction at Oak Ridge.

Résumé. Cet article décrit le nouvel accélérateur et laboratoire en construction à Oak Eidge.

At Oak Ridge we are now well into the first phase of a major expansion of our heavy ion accel-erator facilities. This present phase, begun in late 1974, will include a 25 MV tandem electrostatic accelerator, a building to house the tandem with some additional experimental areas for use with the ion beams directly from the tandem, equipment to transport heavy-ion beams from the tandem to the existing Oak Ridge Isochronous Cyclotron (ORIC), and necessary modifications to ORIC so that these beams may be injected and further accelerated.

Figure 1 illustrates the ion energy performance as a function of ion mass for heavy ion beams available presently from ORIC, those expected from the 25 MV tandem accelerator, and those expected from the tandem + ORIC combination. Both the tandem and tandem + ORIC curves assume two strip-pings. The tandem curve is computed for a gas stripper in the terminal and foil stripper in the

ORNL-DWG 7 4 - 2 5 3 6 2 4 | 1 1 1 1 1 20 V — VTANDEM +0RIC £ \ o 16 \ >~ \ S \ >- 12 25MV V g TANDEM \ 8 V S— - \ - 208pb o \ \ . ^ v . BARRIER \ 0 R I C ' ' ~ ^ . o I 1 -^ 1 1 ' 0 40 80 120 160 200 240

ION MASS (amu)

Fig. 1. Beam energy as a function of ion mass for the s e p a r a t e and combined a c c e l e r a t o r s .

high-energy accelerating tube. The tandem + ORIC curve is computed for gas stripping in the terminal and foil stripping in ORIC. Both cases assume selection of the most probable charge state fol-lowing each stripping so that both curves could be raised slightly (at the cost of intensity) by going off the peak of the charge state distribution.

The dashed line marks the position of the Coulomb barrier for any of these ions on a lead target nucleus. Roughly speaking, to study proc-esses that involve nuclear reactions we need to have an ion with energy greater than (above) this line. Thus for ions heavier than about A=95 such studies will require using the ORIC to boost the energy of the tandem beams.

When not operating in the coupled mode, the two accelerators will operate independently supporting two experimental groups.

The total cost of the present project will be about 17% million dollars and completion is sched-uled for May 1979.

1. Tandem Accelerator.

The 25 MV electrostatic accelerator is being procured commercially from National Electrostatics Corporation. The design and fabrication of the accelerator system will be provided by NEC follow-ing detailed technical specifications developed by the Oak Ridge group.

The most novel feature of the new tandem accel-erator is its folded configuration. In this ac-celerator, both "low-energy" and "high-energy" acceleration tubes are contained within a single column. Negative ions are injected into the low-energy acceleration tube and accelerated to the

*Operated by Union Carbide Corporation for the U.S. Energy Research and Development Administration.

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c5- 22 8 J.B. BALL et al. high vslf@$e terminal which is maintained at posi-

tive potential,

the

terminal, the ion beam first passes through a ser*~~@- gpd becomes posi- tively charged. After stripping, ene ,Q@r&e state coagomnt present in the beam is bent by a laagneg through an g&,e of 180' and injected into the high-energy acce%g?gag$~~.tube for further acceleration back to ground poteng$~)$,, n e essential point is that a folded tandem acoelerqtol: rgquires only column structure in contrast to a c9Il;ven- tional or "lins&r" tandem accelerator which employs two column structures, ~ k l d e ga each side of the high voltage terminal.

The basic layout of the accelerator is shown schematically &a pig. 2 and performance parameters are listed in Table 1.

The foundation of any elect~~&jt& accelerator is its column structure. In this machine, the column will built in 24 inch high modules consisting of 4 inch thi& horizontal cast aluminum bulkheads supported by 16 clrernferentially located colum posts of the type used in previous NEC de- signs. The eglpnn structure will have a diameter of l1 feet and a Iengeh of 62 feet, excluding the high voltage terminal. The R%& v~ltage terminal will have a diameter of 13.3 feet and

a

h&&t of 16 feet.

The acceleration f&gg will be the standard NEC design used in virtually all o f g b i r previous accelerators. These are fabricated of titapivq and alumina ceramic bonded together with an all-metal seal. They utllizs flat,field electrodes and are designed to operate at u1txwk;igh vacuum. Voltage grading for each acceleration tube and the column structure will be provided by three enclosed corona discharge tubss,

Two independent grewpB of three pelletron chains will be used for charge trsnspgpt to the high volrage terminal. These systems togeizher

~ $ 1 1

deliver a current of 600 pA. Provision has also been made for fut;stxe installation of an additional group of three chains to

raise

the total charging capability to 900 pA. Power for various components within the column structure will be provided by fwr, rotating shafts, each capable of transmitting 50 horsepower.

Service for the col- structure and contents of the high voltage tennlnal will,

be

performed from two movable service platforms. The l a r p annular platform will be located in the space between $he column and pressure vessel. A small platform

called the "column service platform" will move vertically within the eel- allowing egsy accgss to the interior of the column structupe and high voltage terminal.

The accelerator will be insulated by pure SF6 gas aoptained within a pressure vessel 98 feet long

and

33 Seet in diaefer, This vessel, with a maximum design presgmg p f 110 psig, pill weigh approximately

438 tone

empty and appro~imately 500 tpns when the column structure and associated e g u i p ~ e ~ t i g installed.

Another sige&£isa~g.~r~gk the tradition of electrostatic acceleraeo~s &S

w$Eh

_{G ~ Q ~ F @}_o&₉ control system: our system will be based entirely on digital c~mmunicat%~n te~hniques

,

Although dlgital computers will play B very important role in the control syatera, sgrictly speaking we are

not

going to have a "computer control system." That f b l y,e do not plan to have the computers inside any of the %onfrg:!. lop~q of the accelerator performing control fun~ti~ne wiGhg1~t P?er@tIPr intgmcnti~q. We believe that conveneia~~% sgg$ep W ~ W R logps

(e.g., "corona stabilizer") will perf o w satis- f actorily wf th only m i w r ekanges

.

Initially, the task ef the digital elements of the control systemwlll

be

ta prsvide lllultiplexed communication of the information between the sper- ator and the accelerator. This will greatly reduce the amount of signal wiring required and will facilitate implementation of the two identical con- f ~,censoles ~ l required (one for use with ORIC and

nee whes

rke

gqndenl i~ used by itself). Although not ~ a a p u t e ~ -.

W B R G T P L ~ ~ ~ ~

tkg ,qpp&ert)~or will be computer controllable, Pp@yi&egg haye been in: corporated to insure, as we learn how she accelerator behaves, that we can gradually cesch

the

WP- puter to take over some of the human operators' tasks.

2. Building.

The new building for the tandem accelerator adjoin8 ggce gresent ORIC building. It consists of a three-story addition y$pF a tower housing the tandem pressure vessel. The tower will have a diameter of approximately 45 feet and will rise 160

feet abgve grqpnd. A sectional view is shown in Fig. 3, The shielding, ranging up to four feet of

concrete, provides adequate prntactiop for % l PYA

of beams with A >

4

at 'all energies,

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HEAVY I O N RESEARCH FACILITY AT OAK RIDGE

Table 1. Tandem Performance Parameters Ion Mass:

Analyzed Beam Intensity: Maximum Analyzed Beam Emittance Operating Terminal Potential: Typical Beam Energy Stability: Injected Ion Energy:

Injector Magnet: a) mEIq2

b) minimum mass resolution Analyzing Magnet:

a) mE/s2

b) minimum energy resolution

12 to 250 1.0 pllA

*0.4

[l

+

( q+1)112]/(l+q)1'2 IT cm mrad 7.5 to 25.0 MV

+2 keV X accelerated ion charge number 150-500 keV

ASSEMBLY PORT 4VENTILATION PORl

HIGH VOLTAGE TERMINAL

TERMINAL BENDING MAGNET ELECTROSTATIC

OUADRVPOLE LENSES

PRESSURE VESSEL ACCELERATION TUBE

MINOR DEAD SECTION

ELECTROSTATIC ION PUMP AND ELECTRON TRAP [TYPICAL)

UPPER MAJOR DEAD SECTION

COLUMN STRUCTURE MINOR DEAD SECTION

ELECTROSTATIC OUADRUPOLE LENS LOWER MAJOR DEAD SECTION

SUBLIMATION PUMP MINOR DEAD SECTION

AND ELECTRON TRAP (TYPICAL)

AR SERVICE PLATFORM WN IN REST POSITION ELECTROSTATIC OUADRU

ACCELERATION TUB

INJECTOR MAGNET (MA MAGNETIC OUADRUPOLE LENS

ENERGY PRODUCT l 2 0

BENDING MAGNETS

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J.B. BALL et al.

I L A l l D R S H I F T LYO TAY[ PORTS

L

ROTATtO 90' FROM TRUt POSlTlON

Fig. 3. Elevation view of new facility

The post-accelerator beam is analyzed by one of two magnet systems. The first, consisting' of fixed 25' and 65' magnets with p = 10 ft, is for inject- ing the beam into the ORIC cyclotron. The mass energy product of 735 was chosen to bend any tandem beam with charge state near the equilibrium charge

state as produced by a gas stripper at the tandem terminal. The second system is 'a single 9 0 ° , p =

63 in. magnet on a rotatable mount that is used to inject the beam into any beam line in two new experimental areas, This magnet with mass energy product of 320 will bend any beam from the tandem that has sufficient energy for nuclear physics studies.

Figure 4 shows the total experimental facility for both machines including the existing beam lines. The existing lines are used with ORIC alone or with'the tandem and ORIC coupled. The location of eight proposed new beam lines are shown ema- nating from the tower base.

3 . ORIC Modifications.

'To further enhance the research capabilities of heavy ion beams produced by the tandem, the existing cyclotron, ORIC, will be suitably modified to serve as an energy booster. Thus, ions accelerated in the tandem will be transported to the ORIC, injected into the center of the cyclotron and then accelerated to full energy.

As shown in Fig. 5, the beam will enter the cyclotron through the dee stem, and be directed by an inflection magnet so that after enteri~g the

COUNTING ROOM ATTERING CHAMBER

SPECTROMETER

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HEAVY I O N RESEARCH FACILITY AT OAK RIDGE

Fig. 5 . The i n j e c t i o n of a n 1 2 7 ~ beam i n t o ORIC

magnetic f i e l d i t is' tangent t o an o r b i t s u i t a b l e

f o r a c c e l e r a t i o n . A f o i l i s l o c a t e d a t t h e p o i n t

of tangency t o s t r i p t h e beam t o a h i g h e r charge

s t a t e s o t h a t i t can b e contained i n t h e magnetic

f i e l d . A f t e r s t r i p p i n g , t y p i c a l l y about 20% of t h e

beam w i l l b e i n t h e a p p r o p r i a t e charge s t a t e f o r

a c c e l e r a t i o n . I n t h e f i g u r e a beam of 225 MeV

1 2 7 ~ 8 + s t r i p p i n g t o 32' and being a c c e l e r a t e d t o

725 MeV i s used a s an example.

The f o i l p o s i t i o n e r w i l l b e designed t o accom- modate a "magazine" of s e v e r a l f o i l s s o t h a t new f o i l s can b e i n s e r t e d i n t o t h e beam e s s e n t i a l l y i n s t a n t a n e o u s l y without breaking vacuum o r a l t e r i n g t h e p o s i t i o n of t h e f o i l h o l d e r .

4 . Phase I 1 Booster A c c e l e r a t o r .

While c o n s t r u c t i o n is p r o g r e s s i n g on t h e p r e s e n t

f a c i l i t y , we have been a c t i v e l y pursuing a d e s i g n study f o r a Phase I1 b o o s t e r capable of a c c e l e r - a t i n g a l l i o n s t o e n e r g i e s i n excess of t h e Coulomb b a r r i e r .

Our Phase I 1 p r o p o s a l i s based o n a s e p a r a t e d

s e c t o r c y c l o t r o n w i t h a n energy c o n s t a n t of 400.

The s e p a r a t e d s e c t o r machine would b e l o c a t e d s o

t h a t e i t h e r t h e 25 MV tandem o r t h e ORIC could

s e r v e a s t h e i n j e c t o r . The energy performance of

t h i s b o o s t e r a c c e l e r a t o r i n j e c t e d w i t h t h e 25. MV

tandem i s compared w i t h v a r i o u s a c c e l e r a t o r s i n

Fig. 5. The time s c a l e f o r c o n s t r u c t i o n i s such