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

Accelerat ion Test of Heavy-Io n with TIT RFQ LinacNoriyosu HAYASHIZAKI, Toshiyuki HATTORI, Kimikazu SASA, Takashi ITO,Katushi ISOKAWA and Satoshi MAJIMA
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
2-12-1, 0-okayama, Meguro-ku, Tokyo, 152 JAPAN

Abstract
A heavy-ion acceleration system with the TIT-RFQ has
been developed. The TIT-RFQ was designed to. accelerateparticles with a charge to mass ratio E 01: 1/16, as it was, thekind of particles was limited because of the insufficientwithstanding voltage of the beam injection equipment. Inorder to solve this problem, the development of the newsystem was planed, and the work has been carried out sincelast year. By using this system, the first acceleration of N+
beam was observed in January this year; however, the beam
intensity was insufficient. Some problems were pointed out,
and the synchronous circuit of a RF pulse was constructed
up to now. By using this circuit, the increase of the beam
intensity was observed in the second acceleration test in thissummer.

stably both of particles. The first and second acceleration
tests, however, were performed for N+ and He+ because of theinsufficient aging of the accelerator. The new system
consists of the TIT-RFQ, a hexapole cusp-field type ion
source, acceleration columns, a solenoid lens, an einzel lens,magnetic quadrupole lenses and an analyzing magnet. The
arrangement of the system components shown in Fig 1, andthey are described the following.

TIT-RFQ
The TIT-RFQ constructed on 1993 is 4-vane type RFQ
linac[5-6]. The principal parameters are shown in Table 1.
The beam transmission efficiency observed in the previoussystem was 90 % of the expected value.
Table 1 Principal parameters of the TIT-RFQ
Charge to mass ratio
01: 1/16
Operating frequency [MHz]80.9
Input beam energy [keV/u]
5.0
Output beam energy [keV/u]
219.0
Normalized acceptance [rtmm·mrad]
0.5
Duty factor[%]
10.0
Expected beam transmission [%]10 rnA input
91.8
0 rnA input
68.4

1 Introductio n
The TIT-RFQ has been operated for the basic researches
on heavy-ion inertial fusion and ion-pumped laser[1-2]. Toaccelerate heavy-ions with the TIT-RFQ is very importantto perform more effectively the experiments, and moreover,
it is interesting to estimate the performance of theaccelerator. The TIT-RFQ was designed to accelerateparticles with a charge to mass ratio E 01: 1/16 from 5 keV/u
up to 219 keV/u. As it was, the acceleration particles werelimited to the ones with E 01: 1/4 because of the insufficientwithstanding voltage of the beam injection equipment.
In order to solve this problem, the development of a new
heavy-ion acceleration system was planed, and the work has
been carried out since last year. By using this system, thefirst acceleration of N+ beam was observed in January thisyear; however, the beam intensity was insufficient[3-4]. To
obtain the intense beam, some problems were pointed out,
and the synchronous circuit of a RF pulse was constructed
up to now. By using this circuit, the beam intensity of six
times of the asynchronous result was obtained in the second
test in this summer. The results of the acceleration test andan outline of the system are presented.

2 Outline of new heavy-ion acceleratio n systemThe previous system has been operated with He+ beam,
and its intensity was 2.5 rnA at the ion source and 1.6 rnAafter the acceleration. In the new system, N+ and o+ with E"" 1/16 were selected as the principal acceleration particles.
The importance in a design was to transport and accelerate

Ion Source
In the previous system, a 2.45 GHz ECR ion source wasoperated; however, its maximum extraction voltage was 25
kV. fu the new system, the hexapole cusp-field type ion
source was constructed and set on the high voltage terminal.
Ions are generated with the microwave of 2.45 GHz of apulse mode. The input beam energies of N+ and o+ are 70
keV and 80 keV, respectively. It is obtained by using theextraction voltage from the ion source and the acceleration
columns with the withstanding voltage of 40 kV and 60 kV,
respectively.
The qualities of the beam extracted from the ion source
were measured for He+ and N+. The measurement system
consisted of the ion source, the einzel lens and a small
analyzing magnet. The extraction voltage and the duty of thebeam pulse were 20 kV and 17 %, respectively. In the beam
spectrum measurement, the generated rates of N+ and N2+
from N2 gas were observed 18 % and 91 %, respectively.
The maximum average intensity of N+ was 14 ~-tA, and byconsidering the pulse duty, this result corresponds to thepeak intensity of about 80 !J.A The generated rate of He+
was greater than 99 %, and its intensity was 80 !A-A

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The 11th Symposium on Accelerator Science and Technology, Ha-,:ima Science Garden City, 1997

Hexapole Cusp-Field typeIon Source
SolenoidFCJ

High-Voltage
Terminal
Analyzing Magnet

Acceleration Einzel Lens
Columns
50cm

Fig. 1 Schematic drawing of the new heavy-ion asseleration system

Beam Focusing
A focusing force of an electromagnetic lens must
increase in proportion to beam energy. Therefore a solenoid
lens without the problem of electric discharge was selected
as the substitute for the einzel lens. The maximum
magnetic field of this lens is 6.8 kG, as it is, it is 3.8 kG atpresent because of the limit of a power supply. The einzel
lens was remained to assist the solenoid lens. The triplet
magnetic quadrupole lenses of an analyzing system wereunchanged.

3 Improvement of RF synchronization
The first acceleration of N+ beam was ·observed by using
the new system in January this year; however, its intensity
was nA order. TI1e causes of this problem were theasynchronizaton of the RF pulse and the beam pulse, theinsufficient beam extraction from the ion souse and theinsufficient beam focusing. TI1e cycle of RF pulse of theTIT-RFQ is vapable in 30 - 300 ms. The one of beampulse is invariable on 20 ms. In the first test, the beam wasaccelerated with the RF cycle of 33 ms; the synchronous
cycle of 100 ms. The observed beam had a beat because thesynchronization was insufficient, and the beam transmission..efficiency was 0.2 - 0.3 %. In order to this problem, thesynchronous circuit of the RF and the beam wasconstructed. The signal picked up from the ion source ismodified by the circuit of Fig 2, then, it is sent in theaccelerator controller. By using this circuit, it was possible
to accelerate the beam with synchronous pulse of 20 ms
cycle. The improvement of the ion source and. the focusinglens is performed in the near future.

4 Acceleration Test
TI1e acceleration test with the syncbronous circuit wasperformed for N+ and He+. The measured beam property werethe beam spectrum and the relationship between the beam
intensity and the RF power fed to the accelerator. The widthof the RF pulse was 150 JA.A for N+ and 300 JA.A for He+
because of the duty. The maximum RF power was 60 kW
in this test; however, the sufficient power to accelerate W
beam is 80 kW. The total intensity of N+ and N2+ at FC 1
was 27.5 f.I.A, and the one of He+ was 52 JA.A. The
accelerated beam was measured at FC 3.
The energy spectrum of N+ beam accelerated with thesynchronous circuit is shown in Fig. 3. Its peak energy was
3.07 MeV, and the energy distribution was :1:: 0.07 MeV. In
the asyncronous acceleration, the sawtooth spectrum wasobserved because of the beat of a pulse.

N+: 3.07 MeV

FOJL0RF Power54.1 kW
Solenoid current 3.8 kG
Einzel voltage
17 kV__________
0on slant Fraction
Discriminators___. ' - - 10

Magnetic fletcl [kG]
Fig. 3 Energy spectrum of the accelemted W beam.

Fig. 2 Schematic drawing of the signal modifier-213-

The II th SymRosium on Accelerator Science and Technology, Harima Science Garden City, I997

The relationship between the beam intensity and the RFpower for N+ is shown in Fig. 4. Tiw maximum averaged
intensity in. synchronous result was 15 nA, and it was six
times of the one in asynchronous result. Tile RF power of
45 - 60 kW for N+ corresponds to 3.7 - 4.8 kW for He+.
Tiw results for He• are shown in Fig. 5. Consequently, thestarting conditions of the acceleration of both are similar.
T11e intensity of N+ will be increased and saturated byincrease of the RF power. T11e beam transmission efficiency
is estimated after the emittance measurement presently.

5 Conclusion
TI1e heavy-ion acceleration system with TIT-RFQ has
been developed. By using this system, the acceleration of N+
beam was possible. In the second test with the synchronous
circuit, the maximum averaged intensity of 15 nA for N+
beam was obtained, and it was six times of the one inasynchronous result. The beam transmission efficiency isestimated after the emittance measurement presently.
The new system cannot be applied for the experiments
because of insufficient intensity. In order to increase thebeam intensity, we intend to power up the solenoid lens andthe RF power in this year. T11e improvement of the ion
source is planed after next year.

1.6 .......-~..-.-~~..........~...........~.-.-....,;--..........,~ 1.4

g 1.2"'
=~
1.9

E 0.8

---------------'-----________-------------·--····

References::::r~ynchr~nizatio~[----··;·······-_·--- -~____····-r. -..... -..... --,::.::::::::::::::::~~~..... .

.c 0.6--. :... -.. -- .. --.-- .. ~ .. -......... ---~~ 0.4~~ 0.2

RF Power [k.W]
Fig. 4 Relationship between the N+ beam intensity andthe RF power. T11e focusing conditions of the solenoidand einzellens were 3.8 kG and 17 kV, respectively.

[1] K.Sasa et al., Fine-focusing system of intense beams forapplication of ion-induced plasma, Nuclear Instruments
and Methods in Physics Research, B113(1996)67-70[2] K.Sasa et.al., Measurements of plasmas induced by 4He+beams from r.f.quadrupole linac, Fusion Engineering andDesign, 32-33(1996)547-550[3] N.Hayashizaki et al., Heavy-ion acceleration experimentson RFQ Linac, Proceedings of the 16th RCNP Osakaintenational symposium, to be published.
[4] N.Hayashizaki et al., Acceleration test of heavy-ion in
RFQ Linac for HIF basic experiments, Proceedings ofIAEA Technical committee meeting, to be published.
[5] M.Okamura et al., Design and construction ofheavyon RFQ linac with effective acceleration structure,
Nuclear Instruments and Methods in Physics Research,
B89(1994)38-41[6] M.Okamura et al., Acceleration test of heavy-ion RFQ
linac at TIT, Nuclear Instruments and Methods inPhysics Research, B99(1995)694-696

120r-----~~--.-~---.--~-,

~ 100
0·~

....

80

~

----------····-····-· ---------························----~---·····-·······--·-----(Synchronization! ------········-- · ---------·1·--------------------:·······--------------------.960----------1·------------------··!-·············~

40 ················ell~ 20 ..... ·--·--···:t::.:·::.:::::::::::r~-;~~~i~;~~i~~~i~J::.
!

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2030.--.; ...... ········· --- ---~--·········· -------- ~---- ----------- -·· ..

1040

RF Power [kW]Fig. 5 Relationship between the He+ beam intensity andthe RF power. The focusing conditions of the solenoidand einzellens were 3.8 kG and 0 kV, respectively.

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