The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Cocktail Beam Acceleration Technique at JAERI A VF Cyclotron (II)Ikuo ISHIBORI, Mitsuhiro FUKUDA, Susumu OKUMURA, Kazuo ARAKAWA, Hiroyuki TAMURA,Watalu YOKOTA, Takashi AGEMATSU, Takayuki NARA, and Yoshiteru NAKAMURA
Advanced Radiation Technology Center, JAERI
1233 Watanuki, Takasaki, Gunma 370-1292, Japan
minutes for this purpose. By using more than one methodsof low dee voltages, frequency change and the new gas feedsystem, 12C 3+ and 2 ~e5 + beams can separate from 160 4+ •At the JAERI AVF cyclotron, an cocktail beam
The paper reports the modification of the ECR ion
acceleration technique by means of RF frequency change isused for ions with mass to charge ratios (M/0) nearly equal to source, combined use of methods to improve the M/0
4 and 5 in routine operation. In case of M/0"'4, mass-to- resolution or to reduce intermixture of different ion species incharge ratio difference between species are comparable to or cyclotron beams.
less than a value of separation limit defined by the M/0
2 Modification of Gas Feed System forresolution of the cyclotron. This makes it difficult toECR Ion Source
separate ion species with the cyclotron. In order to purify
the cyclotron beam, methods of applying lower dee voltages,
Injection of a single ion species into the cyclotron isfrequency shift from the optimum values or injection ofbeams of a single ion species were examined A gas feed one of the ways to purify cyclotron beam without improving
system of an ECR ion source was modified to produce beams the M/0 resolution. The key to this purpose is reduction ofof a single ion species and to reduce gas changing time. The time to change gases. Our ECR ion source, OCTOPUS,
M/0"'2 cocktail ions were successfully accelerated using has a big gas feed system with 14 gas cylinrers mounted inthose methods recently.
three cabinets. Pressure regulators and pneumatic valves areplaced close to the cylinders. Gas change is remotely made1. Introduction
with the pneumatic valves. The length of tubes between thepneumatic valves and the leak valves were originally about 3"Cocktail beam" is mixture of ion beams of pluralm. Because of the long tubes and the large volume in them, itspecies, which is usually produced with an ECR ion source.
a gas fromIn the technique of cocktail beam acceleration, cocktail ion took more than an hour to satisfactorily evacuate
beam are injected into the cyclotron, accelerated the tubes. In the new resign, the pneumatic valves were
simultaneously and extracted separately. Ion species are moved on a high voltage board , on which the leak valves areselected by slightly changing the RF frequency or the mounted, and the tube length was reduced to 35 an. The
magnetic field The primary advantage of this technique isschematic design of the new gas feed system is shown in Fig.
shortinenergy
beamandto enable us to change ion species
1. After this simple modification, the gases can be changed
time. Requirements of the cocktail beams have increased asin several minutes.
beam applications have been diversified in research field ofmaterials science and biotechnology. Ranges required inbeam energy and ion species are increasing as well.
OCTOPUS
Cocktail ions with M/0"'5 can be separated by thecyclotron simply by changing the RF frequency and they
have been supplied to research experiments since 1998.
In the revelopment of the cocktail beams acceleration
with M/0=4 using ions of 12C 3+, 160 4+, 20Ne5+ ions, 12C 3+ and
20 Ne5 + were observed in the beams optimized for the 160 4 +.
The M/0 difference, ~(M/0)/(M/0), of 12C 3+ and 2~e5 + from160 4 + are 3.2x10·4 and 0.6x10 4 , respectively (see Table 1).
The reason of the intermixture is that they are comparable toor less than separation limit of the cyclotron of about 3x 10 4
which was experimentally and theoretically estimated[1 ].
In order to improve the M/0 resolution of the cyclotron,
lower me voltages, intentional shift of the RF frequency
from the optimum value were examined [1,2]. In order tomake the best use of quick change capability of the cocktail
main gases
beam acceleration, we also adopted injection of a single ion
Fig. 1 Schematic drawing of the new gas feed system
A gas feed system of an ECR ion source
species.
of the ECR ion source.
(OCTOPUS) was modified to change gases in several

Abstract-453-The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Nitrogen, which has M/Q values sufficiently different
from 4, is used as a common support gas to save time forpurge in the tubes. In every change of gases, evacuating theprevious gas and filling the next gas are oone in turns twotimes each. This operation takes only about 7 minutes.
The ions of 12C 3+ are produced from C02 gas.
Therefore a comparable amount of 16 0 4+ ions are injected into
the cyclotron with 12C 3+. If we use another gas without
oxygen, oxygen ions will be considerably reduced
However, oxygen ions are always observed in beams from theion source, which are probably produced from water and airleak of the chambers. For this reason, a<klitional methods
described in the next section are necessary to obtain 12 C 3+ or
20Ne5+ beams free from 16 0 4+.

3 Methods to Improve M/Q Resolution
We use two methods to improve the M/Q resolution;1) lowering dee voltages than those of regular operation,2) shifting the RF frequency from the values optimum for a
specific ion species. Each method causes increase of tumnumber of ions to reach the extraction radius. Ions which do
not satisfy isochronous condition will phase-out if increaseof the tum number is sufficitent. Details of the principles
and the test operations are reported in Ref. 1 and 2.
We use the method 1) in practical cocktail acceleration
for M/0"'2 and 4 because it is more effective.

development since higher performance in production ofhighly charged ions were required for fully stripped ions.
Fig. 2 shows pulse height spectra for M/0"'2 cocktail
beams measured using a plastic scintillator with the RFfrequency changed step by step. For the spectra in Fig. 2-a,
mixture of more then one gases of He, C02, N2, Ne and 36Ar
were used and the dee voltage values were for non-cocktail
acceleration, about 38 kV. As the RF frequency increased,peaks of smaller M/0 ions appeared and peaks of larger ones
disappeared There were more than one peaks in every
spectrum because of the insufficient separation. For theother spectra in Fig. 2-b, individual gas was used (N2 gas wasnot used in this case) and the dee voltages were lowered by 3kV. As a result, a single peak of one ion species appeared ineach spectrum. A ratio of impurity 160 4+ in 12C 3+ beam was
0. 7 % in this measurement. Fully stripped ions of 36Ar
were observed in the spectrum. Its beam was too low to bemeasured with a Faraday cup and was estimated of the order of0.1 epA from the count rate and the beam attenuation rate.

Table 1

Parameters of M/0"'2,4 and 5 cocktail ions.

M/0 ion~(M/0)/(M/0)

4 Use of Isotope for Larger M/Q Difference
Ions of 84Kr1+, a member of M/0"'4 cocktail, areproduced from a krypton gas. In a pulse height spectrum of
cyclotron beams, 56Fe14+, 52Cr13+, 40Ar10 + and 36Af'l+ are
observed as background ions with 84 Kr1+ as reported in thelast symposium [3].
The Ar ions may come from
impurities in the krypton or nitrogen support gas or from airleak into the ion source.
The metallic ions perhaps
originate from plasma chamber of the ion source.
Elimination of background ions is extremely difficult even if
we use the methods mentioned above because their M/Qdifference from Kr ion is too small. We can use anotherisotope of Kr because it has many stable isotopes. The M/Qvalue of 78 Kr 19+ is different enough from the background ions'.
Optimization of the frequency to the isotope ion and gaschange was made in ten minutes. No background ions wereobserved in the 78 Kr19+ pulse height spectrum.

2

4He2+
14N7+
12c6+
1608+
zoNe1o+RF frequency(MHz)energy(MeV)

12.44811012.454385

12.456330

12.4604404.3x10-4
2.2x10-4
3.2x10-4
0.6x10-4

12.461550
5.3x10-4
36Ar18+12.467990----------'---------------- ---------------4 4He+
11.90825
6.5x10-4
12c3+
11.91675
3.2x10-4
1604+
11.919100
0.6x10-4
zoNes+
11.920125
5.5x10-4
40Arl0+11.926250
1.3x10-4
84I<r1+
11.928525----------------------------------------1sN3+

5 M/Q•2 Cocktail Beam Development

5

A cocktail of M/0"'2 (fully stripped ions !) is one of
the most required ions in the research fields of materials
science and biotechnology, since one can use the highest
beam energy with the cyclotron for each ion species. The
parameters of M/0"'2 cocktail are listed in Table 1. A new
ECR ion source (HYPERNANOGAN) [4] was used in this-454-

zoNe4+
40M+

84Kr17+2.2x10-4
3.2x10-4
0.6x10-4

13.86756

13.87375

13.881150

14.047323-----------------------------------------------------

The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

6. SummaryReferences

We succeeded in purifying the cyclotron beams ofM/Qe2 and 4 cocktails by applying more than one methodsof low dee voltages, RF frequency shift and injection of asingle ion species. Use of lower dee voltages or RF
frequency shift leads to reducing beam intensity of main ion
species as well as impurity ion species. Additional tuning
As we gain ourtime is necessary to keep beam intensity.
operational experiences, the tuning time may be shorten.
But further revelopment to improve the M/Q resolution,
especially for separation of 160 4 + and 20Ne5+.
Now we use the injection of a single ion species also
for M/Qe5 cocktails, which simplifies operation of thecyclotron and the ion source.

[1] W.Yokota et al., "Cocktail Beam Acceleration Technique
at JAERI AVF Cyclotron (I)", this meeting[2] M.Fukuda et al., "Acceleration of Cocktail Ions at JAERIAVF Cyclotron", PAC99, New York, March 29 (1999),
in press[3] M.Fukuda et al., "Development of Cocktail BeamAcceleration Technique for the JAERI AVF Cyclotron",
The 11th Symposium on Accelerator Science andTechnology, Harima Science Garden City, (1997) 139[4] T.Nara et al., "Beam Generation Test for
HYPERNANOGAN and Modification of 18 GHz ECRIon Source at JAERI Takasaki", this meeting

(b)

(a)
300r--L250f-fRF=12.446 MHz-200r---150

f-100r--10050f-'I

O···+·

00 ··I.

~~ I

I'' 1000

I '' 1500-

2000

l111lmht

0l.

I'Il

2000

1500

1 000

500

250-200fRF=12.452 MHz _-

12c

150

100...

...

150

s::::: 300

s:::::::J 100

00

III40016Q_I_fRF=12.458 MHz _-::J 200

0050-100oIII ·1 .. 1 1~ •I• I • I500I

50080.

II

I

I I

1000

1500

2000

IIt

400

20 Ne
300
200100ol

III

I ... 1..111...1.. 1.. ·1500

100

16Q

1000

I I

II III

1500f RF=12.466 MHz

•oo

36 Ar

80
40060

III

2000

-40-

200
200" II0ol

It I

0 b...J..__[_!.._!.___J___JL._J.__J___J'---'-'1'--"""'""""--.Ll'-'1'-'--'-'-''--'--'...ul,J
500

2000

0500

1000

1 500

2000

Channel Number

Channel Number

Fig. 2 Pulse height spectra for M/Qe2 cocktail observed with a plastic scintillator. The RF frequency was changed stepby step. In case of a), mixture of plural gases of He, C0 2 , Nz, Ne and 36Ar and the dee voltage values forregular acceleration were used. In case of b), individual gas (N2 gas was not used) and lower dee voltages were used.

-455-