The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Application of an ECR ion source to the JAERI tandem accelerator
Makoto MATSUDA, Suehiro TAKEUCHI and Chiaki KOBAYASHI*
Department of Reactor Engineering, Accelerators Division,
Tokai-mura, Naka-gun, Ibaraki-ken, 319-11 JAPAN

Abstract
We have pushed forward an installation plan of anelectron cyclotron resonance (ECR) ion source in theterminal of the JAERI tandem accelerator in order toincrease beam intensity, beam energy and beam species.

ailplane is applied for the 10GHz RF source, and is set inthe airtight vessel to keep it at the atmospheric pressure.
For the vacuum system, an ion pump is used to enclose agas flow. With an ion pump, noble gas ion extractions
from the source were sucressfully examined for a few
months.

1. Introduction
For heavy elements, maximum beam current from atandem accelerator is limited by the lifetime of stripper
foils. A way for stable acceleration of high intensity
beams is expected to be opened by the use of the ECR ion
source, since the beams from the source are highly
charged and intense.
The operation without foilstrippers bring us no influence of a change in theterminal voltage on the charge state of the beams. Inaddition, it is poosible to accelerate noble gas ions, which
are impoosible fur tandem accelerators. A compact ECR
ion source, called ''NANOGAN' [1,2], with a permanent
magnet structure has been developed at GANIL, France,
for accelerating the radio active ions [3]. Its size andreliability fit our plan.

exlraclor

uhf wcndow
1nsulalor

Fig. 1

2. Mount for the tandem terminal
Many difficulties have to be solved to install thesource in the tandem terminal, such as problems withthe limited space, power supply, cooling system, RFsource, vacuum system, control system and beam optics.
Some measures should be also taken into consideration
against electronic discharges and high pressure, because
the source environment is on a high voltage of 16 MV
and in the high pressure gas of 0.451\1Pa In spite ofthese difficulties, we could find some steps for solving
alxwe problems. The problems with the space, power
supply and control system will be solved by thereplacement of the Duo-plasmatron type ion source,which has been used so far, to the ECR ion source withsome modifications. A 'IWT-type amplifier made for

NANOGAN : mechanical structure

3. Source optimization
Several experiments with the ion source until now
have pnNed the performance as expected. The optimum
condition and the simplification of the operationalparameters were searched on the assumption of
installing the ion source in the tandem accelerator. The
results of this experiment enabled us to reduce the six
operational parameters to the three, which were the gas
flow, bias voltage and the RF power. 'This experimental
procedure was brought from the experimental purpose,
which was not to obtain maximum perfurm.ance of theion source, but to obtain stable intensity of ion beams
against a change in the operational parameters. In* Nihon Advanced Technology. Co.

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The 11th Symposium on Accelerator Scien,ce and Technology, Harima Science Garden City, 1997
/addition to main gas, support gas as electron supplier
were needed to obtain highly charged ion. For Ar ion,Fig. 2 indicates meaSured current intensities of different
charge sta~ as a function of mixing ratio. 'The highly
charged ion (8+,9+) current do not depend on the gas
ratio. So, the q:>timum ratio was chooen to be
Ar:OF1:10 in order to restrain the load of the ion pump.
Extracted current of Ar ions are shown in Fig. 3 as afunct;ion of RF power. Since the beam currents werechanged gently, current adjustment can be attained by
the control of RF · power. RF tuner could .be fixed,
because beam intense was not changeable with a RF
tuner adjustment 'The gas flow, or the vacuum of thesystem was the critical parameter fur the stableq:>eration. For ArB+" ion, it was 1.6X1(}4 (±200/o) torr·J/sec q:>timum. . A calibrated leak source was used furthe gas-flow adjustment ADC bias to the bias electrode(Fig. 1) was necessru:y to produce intense beam. With aDC bias apply of about 4(}----200V, a beam current wasextracted at least ten times as intense as without the bias.
'The resu1ts of the experiment fur three gases, Ar, Kr andXe, mixed with N2 or 02 in above conditions, are shownin Fig. 4 The emittance fur Ar ions from the above
experiment was about 10mm·mrad·MeV!tl (80%) andthe beam profile was vmy complicate.
4. Arrangement'Ihe arrangement of the ion source is planned as isshown in Fig. 5. The ion beams extracted by 30kV fromthe ion source are fucused by an einzellens, and then themass and charge of them are roughly Selected by the40 pre-analyzing magnet The pre-analyzing magnet isused tO reduce the load to the pre-areeleration tube, since
the beams from the ion source amount to 2mA Afteran areeleration by the 80 kV pre-areeleration tube and abeam selection by a 40 analyzing magnet, the beams
are finally led to the tandem areelerator tube. Only asmall part. of beams are to be injected into the tandem
areelerator after reducing the large emittance by several
apertures.

-Ar3+....--------------1 _._Ar4+

35

30 1 - - - " \ - - - - - - - - - - - - j -lr-Ar6+-Ar7+

25 1 - - - - : - - \ - - - - - - - - - - l - A r B +<2; 20-G-Ar9+....c~ 15(.)" 10500

2

46
mixing ratio( 02/Ar)

810Fig. 2 Relation between gas mixing ratio andextracted ion current_..,_Ar4+~81----""'>6';~.,--------ll'"""'.......:::::--:--~,------l~~ 6 ~-~--~~~~-.r-~~-~~

84j-...X.---J~~i6..-<:)o;;;;;;;;;~~--+

0 ~--~--~---~--~
020
60
4080
RF Power[W]Relation between RF power and extracted ion

Fig. 3current.

181614";? 12liiiAr 1•Kr 1DXe 1-~~10'

1:~~

86~ 4I" 2..c03nIII. ll456jII l
II. I ll .n ..,7 8 9 10 11 12 13 14charge stateFig. 4 Charge state distribution fur three gases, Ar, Krand Xe, mixed with N2 or 02.

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The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

®

10.0g

5.0

@

1<:..

IIII)l>(v"Ar•- ....... _ -t

1.0+I<,Ku)(Xe• \C)"' 4I0.5

CD ECR "NANOGAN"® einzel lensCD 45° pre-magnet@ x-steerer@lens & pre-ace. tube
@ faraday cup(J) ion pump
@ 45° magnet~electric quadropole

0.1

23
Energy/Mass [MeV/AMU]

45Fig. 6 Expected beam currents in the terminal of atandem accelerator from a terminal ECR ion source(upper three curves) and from a conventional negativeion source (lower three curves).

1000mmace. tube

Fig. 50•:with 2nd stripper

Installation arrangement of the ECR ion source.

5. Expected performance
The expected performance from a terminal ECR ion
source, is showed in Fig. 6. The top three solid curves
are Ar, Kr and Xe currents available from the terminal
ECR ion source as a function of energy accelerated.
Nmnber indicated are the charge states. The threebroken curves are those obtained with the 2nd stripper
foil The three curves at the bottom are for Sn, Cu andCl ions accelerated by the tandem accelerator using anegative ion injector when the terminal voltage is 16MV.
The terminal ECR ion source can provide 10 times more
intense beam currents than a negative ion source does.
Comprehensive examinations including the beam optics
and the control system will be made in the near futureprior to the installation in the high voltage terminal
The installation and the experiments with the ECR ion
source will be carried out in 1998. Acceleration of heavy
metal ions is also considered as our future plan.

Reference[1] P. Sortais et al, Proc. 11th Int. Work on ECR ion
sources, Groningen, 1993, 97.
[2] P. Sortais et al, Proc. 12th Int. Work on ECR ion
sources, RIKEN, 1995, 44.
[3] A Joubert et al, "SPIRAL: a radioactive ion beamfacility project at GANII.:'. Part. Ace. Con£.,Washington 93.
[4] D. K Olsen et al, Proc. lOth Int. Work on ECR ion
sources, Oak Ridge, 1990, 1.

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