JAERI-Conf 95-021

2p1-1
MANUFACI'URE OF THE 6-10 GHZ ffiMPACl' Ern ION SOURCE
WITH AVARIABLE PEIDIANOO MAGNET MIRROR
Eiki Tojyo, Yoshihisa Shirakabe, Yukimitsu Ohshiro, Michihiro Oyaizu, Tsutomu Yamazaki,
Munetaka Fujita, Norio Yamazaki, Mitsuo Nishiguchi and Hideshi Muto
Institute for Nuclear Study, Univ. of Tokyo
Midoricho 3-2-1, Tanashi, Tokyo 188, Japan.
Abstract
Anew small size ECR ion source working in 6-10
GHz is manufactured and now under the first test. Thissource is made of permanent magnets only, and its totalweight is about 40 kg. Its remarkable features are continuously variable axial mirror field, comparatively
large inner diameter of the plasma chamber and radial
multipart windows for an RF injection and a plasma viewing. The variable field is realized by a continuous
replacement of the mutual position of two ring magnets
on the beam axis. The design, manufacture, experimental
setup and intrcxluctory beam test for this new source
are reported shortly.
1. Intrcxluction
Until quite recently, as for a very compact ECR ion
source with permanennt magnet only, there was "NANOGAN"
alone in the world 1 >. But now, such kind of sources arein manufacturing at several insitutes2 >. Usually, typical measures of these sources are within tens of kg in
total weight and roughly within ¢200mmX200mm in outerdimension.
However, these compact sources have commonly a few
problems to be improved. First, the confining magnetic
field is fixed in almost cases and hard to change continuously for the fine tuning of an extracted ion beam.
Second, when the source size is reduced as possible assmall, the inner size of the plasma chamber is also aptto shrink corespondingly. Third, in addition, both alocal heating by the microwave power which is not absorbed into the plasma and the reduced size of the plasmachamber give rise to a hardness of an effctive coolingof the source. Considering these problems, we have developed a new compact ion source with a variable axial
mirror field and with a large size ratio of the plasmachamber compared to the outer total size. Its outline
will be described below.

2. Design Parameters and Structure of the Source
Tab.l shows main parameters of our new ion source.
Especially remarkable points are as follows:(1) The inner diameter of the plasma chamber is set to¢ 60mm. This is the largest value in several same ordercompact sources in the world (Usually, its order is-¢ 30mm). In order to prcxluce a multiply-charged ion
beam as possible as high, it is desirable that the inner diameter of the plasma chamber is over several times
larger than the ancxle hole diameter.
(2) The confining magnetic field can be changed continuously by a replacement of two radially magnetized ringmagnets on the beam axis ( one is magnetized to innerdirection and the other outer direction ). As a result,the axial mirror ratio can be controlled continuously

for an optimization of the extracted beam.
(3) A few quartz windows are mounted in the radial direction into the plasma chamber. These are used for themicrowave port and also as a viewing port. Furthermore,
it is also possible to inJect the microwave power fromsuch multiports, simultaneously. It can be considerdthat the radial injection method of microwave power is
not necessary inferior to an axial one 3 >.
(4) The total volume of the permanent magnet parts are
considerably decreased than the other compact sources.
By this reason, our new source is made with very small
expense. Its volume is a very important measure for compactness, lightness and economy of a source.
(5) Considering that if this source is used for theinjection to an ion accelarator( such as linac or cyclotron), the beam hole diameter is set to ¢ 2-4mm, whichis relatively smaller than many usual cases.
The total weight of the source amount to about 40kg and the plasma chamber is cooled with pure water.
The photograph and sectional views of the new source
are shown in Fig.l and Fig.2 respectively. These designconcept and technology are mainly based on a succeeding
experience of development works for the 2.45GHz compact
ECR ion sources in INs~>.
3. Magnetic Field Configuration of the Source
The confining magnetic field distribution is shownin Fig.3. The solid and broken line denote the simulated results by the POIS&JN code and circled points aremeasured results. The used magnetic material is a neodymium alloy with a maximum BH-prcxluct of 46MGOe(NEOMAX46). The simulated results agree with the measured one
within accuracy of 3%.
As for the axial mirror field, if the ring-to-ring
distance is selected properly to a given microwave frequency, the required ECR field is sufficiently realized
within the axial region in the plasma chamber. corresponding to 6-lOGHz one. On the other side, the radial ECR
field is formed always(that is, independent of the ring-to-ring distance, in the first order approximation )inside the wall of the plasma chamber within the rangeof 6-lOGHz. Very roughly speaking, the maximum distance
between two ring magnets (=130mm) corresponds to the 6
GHz operation and minimum distance (=90mm) to the lOGHz
operation.
Therefore, to a certain given frequency, the extracted beam can be optimized by a fine adjustment of
the initial position of these two ring magnets on thebeam axis. Since these ring magnets are jointed by acylindrical yoke with the dimension of ¢ 190 x ¢ 220 x
190 mm 3 and sectupole magnets are surrounded also by
this yoke, a leakage flux to the radial direction isextremely reduced. Further, as the extractor electrcxle
is made of a mild steel, the axial mirror field is for--218-JAERI-Conf 95-021

med more effectively than in case of a non-magnetic
materic..l.
As in Fig.3, a very strong inverse magnetic field
is formed in the gas-supporting side on the beam axis.
Generally, if a microwave power is injected from thisaxial direction, this feature limits to the effective
absorption to a plasma. But in our case, the microwave
power is injected from the radial direction of the chamber, then the problem does not become seriously.
A more detailed discription on these field configuration is given in our other report&>.
4. Experimental setup
The constructed ian source is set into the injection transport system of the INS-SF Cyclotron. A 45"
bending magnet of the transport line is used as the ion
analyzer. The distance from the ion source to the analyzer is 1827 mm, which is relatively longer compared toan usual setup. Then, in order to arrange the focusing
condition and to realize the calculated beam envelope,an einzel lens, a collimator and a Q-triplet are installed between them. A typical example of the beam trace
is given in Fig.4. The simulation was carried out by
the GIOS code. In this choice, about 50 of the mass resolving power are realized.
The ion source is exhausted by a 300 1/s turbo
molecular pump through both a radial side port of theplasma chamber and the axial anode elctrode hole. The
no-loaded pressure and the working one is 2.1X1Q- 6 Torrand 3-5xiQ- 6 Torr at the beam-extractor side respectively.
The microwave power is injected into this ECR ion
source from the proper microwave system for the large
ECR ian source of the SF-Cyclotron. This microwave source is a klystron amplifier and the operating frequency
is fixed at 6.1 GHz. Therefpre, a lOGHz operation and avariable frequency performance are not scheduled in thefirst beam-extraction test.

References:
1) P. Sortais et al: Proc. of the 11th International
Workshop on ECR Ion Sources; KVI-Report 996; p.97105(1993)
2) Proc. of the 12th International Workshop on ECR Ion
Sources; INs-J-182(1995)
3) E. Tojyo, Y. Ohshiro, K. Oyaizu and Y. Shirakabe:
INS-Rep.-1103(1995)
4) E. Tojyo, Y. Ohshiro, K. Oyaizu and Y. Shirakabe:Proc. of the 11th International Workshop on ECR IonSources; KVI-Report 996; p.234-238(1993)
5) Y. Shirakabe, E. Tojyo, K. Oyaizu andY. Ohshiro:
INS-Rep.-1100(1995)
Table 1
Design Parameters of the 6-10 GHz Compact ECRI S
GHz
6-10
Input microwave frequency
W(C. W.)~200
Input microwave power
kV~30
Beam voltage(desired)-0.5n
Normalized emittanncemm ¢2-4
Beam hole diameter
Inner dimension of plasma chamber >¢60X70 mm 3
¢220X230 mm 3
Outer dimension of bodyDimension of ECR surface 6GHz: ¢=44,L=50 mm (B=2.14kG)
lOGHz: ¢=52,L=65 mm (B=3.57kG)
mm 3¢60X¢140X30
Dimension of ring magnets
mm 3¢20X ¢80X30
20mm (gas injection side)
Stroke of ring magnets
20mm (beam extraction side)mms
6-25X25X60
Dimension of bar magnets
3.1-S.O(gas injection side)
Variable mirror ratio
2.0-3.0(beam extraction side)kg
40
Total weight

5. Summary
A new type of a very small size ECR ion source has
been made using permanent magnets only.
(1) The ihner diameter of the plasma chamber is set to¢60mm. This value is the largest size among thosekind of compact sources in the world, at present.
(2) Its confining fields can be changed continuously bya replacement of the radially magnetized ring magnets.
(3) Since the volume ratio of magnets to a whole of thesource is fairly reduced, the cast reduction for making the source is realized drastically, too.
(4) Based on the experience for manufacture of this newsource, a further advanced version can be designed.
Now the beam extraction has started up. By a very
introductive adjustment, about 600,uA of a total beam
is extracted from an anode hole of ¢5mm at 10 kV, when
the input RF power is 80 W. But in order to produce themultiply-charged ion beam effectively, there are a few
tasks to be done as follows : (!)production of electron
source as a first stage,(2)optimization of the relative
axial position of the anode to the peak magnetic field,etc. These problems will be handled hereafter.
Ackowledgements
This work was supported by the inner grant forscientific and engineering resarch in INS. Authors wish
to thank members of the INS-Machine shop for their exclusive cooperation.
-219-Fig.! Photograph of the ion source

JAERI-Conf 95-021

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