Development of Cyclotron Beam Technology for Applications in
Materials Science and Biotechnology at JAERI-TIARA
Y. Ohara, K. Arakawa, M. Fukuda, T. Kamiya, S. Kurashima,
Y. Nakamura, S. Okumura, M. Saidoh, and S. Tajima
Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute, 1233 Watanuki,
Takasaki, Gunma, 370-1292 JAPAN
Abstract. Recent progress of cyclotron ion beam development for applications in materials science and biotechnology at
the ion-irradiation research facility TIARA of the Japan Atomic Energy Research Institute(JAERI) is overviewed. The
AVF cyclotron in TIARA can accelerate protons and heavy ions up to 90 MeV and 27.5 MeV/n, respectively. In order to
conform to the requirement of a reliable tuning of microbeam formation, the cyclotron beam current has been stabilized
by controlling the temperature of the magnet yoke and pole within +/-0.5o and hence by decreasing the variation of the
magnetic field ∆B/B below 10-5. A heavy ion microbeam with energy of hundreds MeV is a significantly useful probe
for researches on biofunctional elucidation in biotechnology. Production of the microbeam with spot size as small as
1µm by quadrupole lenses requires the energy spread of the beam ∆E/E < 2 x 10-4. In order to minimize the energy
spread of the cyclotron beam, the fifth-harmonic voltage waveform has been successfully superposed on the fundamental
one to make energy gain uniform.
INTRODUCTION
Applications of energetic ion beams with MeVrange energies were initiated more than 50 years ago in
the medical use for the cancer treatment and the RI
production, while application researches for materials
science and biotechnology using the MeV ion beams
have been broadened far later, in the 1990s.
Particularly, the MeV microbeam has become a useful
probe for analytical and biological studies. Microbeam
irradiation and single ion hit is useful for the localized
irradiation, which can be applied to inactivation of
microscopic region of a cell and cell surgery technique.
Microbeams are also useful for analysis of living
organisms using secondarily-produced radiations such
as X-rays and gamma-rays, which are applied to PIXE
(Particle Induced X-ray Emission) analysis and nuclear
reaction analysis (NRA), respectively. These analyses
have been possible with an accuracy of 1µm, since a
microbeam with the spot size as small as 1µm can be
produced from several MV electrostatic accelerators.
On the other hand, energetic heavy ion beams with
energy of several hundred MeV transfer their energy to
materials or living organisms with high-density
ionization and excitation along the trajectory, which
results in microscopically nonuniform dose delivery.
This characteristic is fundamental to induce unique
mutation and local inactivation in living organisms
efficiently. However, the spot size of high energy
heavy ion beams from a cyclotron is still about ten
times larger compared to the beams from an
electrostatic accelerator.
In order to evolve radiation applications based on
these useful characteristics of energetic ion beams, the
ion-irradiation research facility TIARA (Takasaki Ion
Accelerators for Advanced Radiation Application) was
completed at JAERI in 1993, followed by intensive
R&D
activities
in
materials
science
and
biotechnology[1].
The present paper overviews the recent progress on
ion beam development at TIARA to realize a cyclotron
microbeam with diameter of 1µm as small as the cell
nucleus.
CYCLOTRON FACILITY
The TIARA facility consists of four accelerators: a
K110 AVF cyclotron, a 3-MV tandem accelerator, a 3MV single-ended accelerator and a 400-kV ion
implanter. The accelerator complex provides a variety
of ion species from proton to bismuth ions with a wide
range of ion energy from 10keV to several hundred
MeV. The AVF cyclotron can accelerate a proton and
heavy ions up to 90 MeV and 27.5 MeV/n, respectively.
The main parameters of the cyclotron are shown in
Table 1.
The cyclotron is equipped with ten horizontal beam
courses and four vertical branch beam courses as
CP680, Application of Accelerators in Research and Industry: 17th Int'l. Conference, edited by J. L. Duggan and I. L. Morgan
© 2003 American Institute of Physics 0-7354-0149-7/03/$20.00
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shown in Fig.1. In a vertical beam course, an apparatus
for local irradiation of a single living cell is installed, in
which a very low current high-energy heavy-ion
microbeam is formed by a collimation system and
finally extracted into the air through a bottom microaperture. In another vertical beam course, a new
apparatus with a quadruplet of quadrupole lenses has
been installed to realize a microbeam with the spot size
of 1µm.
TABLE 1. Main parameters of the JAERI cyclotron
K-number
: 110
Extraction radius
: 92.3 cm
Number of sectors
:4
Angle and number of dees
: 86o and 2
RF frequency
: 11~22 MHz
Harmonic number
: 1, 2, 3
Maximum average magnetic field : 16.7 kG .
FIGURE 1. Layout of AVF cyclotron and its beam courses
in the TIARA accelerator complex.
RECENT PROGRESS
In order to realize the irradiation of countable
number of ions with the spatial resolution as well as the
targeting resolution of 1µm, we have conducted R&D
on (1)stabilization of the cyclotron beam current,
(2)single-ion hit / lens focusing system, and (3)flat-top
acceleration system. The recent progresses on these
development activities are described in the following
sub-sections.
one, and the variation of the magnetic field ∆B/B has
been suppressed to less than 1 x 10-5, and hence the
beam intensity has become satisfactorily steady as
shown in Fig.3 [2]. The stabilization has led to great
advantages in tuning the microbeam formation.
Yoke
Stabilization of the cyclotron beam current
It is well known in many cyclotrons in the world
that beam intensity gradually decreases after the start of
operation. Since the start of the cyclotron routine
operation at TIARA in 1991, we have experienced a
rapid decrease of beam intensity during several tens of
hours after the cyclotron was excited. The reason has
been identified to be the fact that the magnetic field
strength of the cyclotron drifts by the order of 10-4 due
to a small change in temperature of the magnet yoke by
several degrees[2]. We analyzed the data of the
magnet temperature and the magnetic field of the
cyclotron, and made heat conduction simulation with a
computer code. It has turned out as a result that the
small change of the temperature is due to the heat
conduction from the main coil and the trim coils. In
order to shield or reduce the heat conduction to the
yoke and the pole, a water jacket has been mounted
between the main coil and the yoke(See Fig.2), and the
averaged temperature of the inlet and outlet coolant to
the trim coils and the water jacket has been controlled
so as to keep the yoke temperature constant within +/0.5o. Consequently, the temperature change of the
magnet has been reduced to one tenth of the previous
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Magnet
Pole
Sector
Main Coil
Trim Coils
Water Jacket
FIGURE 2. Cross sectional view of one fourth of the
cyclotron magnet. The heat conduction from the main
coil and the trim coils to the magnet yoke and the pole is
suppressed by the water jacket and the trim coils with
temperature control of the coolant.
FIGURE 3. Variation of the beam current with and
without the temperature control of the magnet yoke.
Single-ion hit / Lens focusing system
A single-ion hit technique is useful to introduce a
large radiation effect to a specific local area of various
biological cells with a countable number of ions. This
technique has originally been developed at several
facilities to hit individual cells in atmospheric
conditions for biomedical applications, though the
beam energies are limited to several MeV[3,4,5]. At
TIARA, the fundamental technology of single-ion hit
was established at the heavy ion microbeam system
installed in the 3MV tandem accelerator facility[6].
This technique has been introduced to a highenergy microbeam system in a vertical beamline of the
AVF cyclotron[7]. A schematic diagram of the singleion hit system is shown in Fig.4. The beams have been
collimated to about 10µm in diameter with a set of
apertures. More than 95% of the collimated ions were
within the mono-energetic peak and delivered to the
aimed local area with targeting accuracy of 85-90%.
The system is equipped with a single-ion detector using
a plastic scintillation counter and a fast beam switcher
in the injection line of the cyclotron. The scintillation
counter occupies one of the ports on the objective lens
revolver for the optical microscope observing samples
on the stage, and detects single ions passing through a
thin target such as biological cells. The single-ion hits
on the target can be realized by setting the beam
switcher 'enable' after completing the single-ion
detection. The spatial resolution of the present system
is ~10µm, as shown in Fig.5.
In order to realize the spatial and targeting
resolution of 1µm, a new system has been introduced
instead of a collimation system[8]. In the new system,
an ion beam is collimated with a set of slits and further
AVF Cyclotron
The Orbit of High-Energy Heavy Ion
Vertical Beam
Line
Collimator
Fast Beam
Switch
Beam
Attenuator Scintillator
Ion Source
Single-Ion Hit
Measurement Module
Micro Aperture
Single-Ion
Sample Stage
Particle Detector
or Objective Lens
FIGURE 4. Conceptual scheme of the real-time single ion
hit system.
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focused by a quadruplet of quadrupole magnetic lenses,
as shown in Fig.6 schematically. The resolution will be
reduced to 1 µm coupled with the flat-top acceleration
system.
Flat-top acceleration
5µm
FIGURE 5. Image of forty Ar ions with energy of
460MeV on CR-39 using a collimation type single-ion
hit system.
Vertical beamline
Steering Magnet
Slits
Beam Scanner
Quadruplet of
Quadrupole
Magnets
Sample Stage
Optical Microscope
and CCD Camera
FIGURE 6. A new microbeam system based on a
quadruplet of quadrupole magnetic lens focusing.
Production of a microbeam with a spot size of 1µm
in diameter using the focusing lens requires the energy
spread of the beam ∆E/E < 2 x 10-4 , to minimize an
effect of chromatic aberrations in the lenses. The
energy spread of the cyclotron beam depends on a
waveform of an acceleration voltage and beam phase
acceptance of the cyclotron. The typical energy spread
of the cyclotron beam is around 1 x 10-3 in an ordinary
acceleration mode using a sinusoidal voltage waveform.
However, the energy spread can be reduced by
utilizing a flattop waveform for uniform energy gain,
which can be generated by superimposing the third- or
fifth-harmonic voltage waveform on the fundamental
one [9,10].
We have designed an additional coaxial cavity to
generate the fifth-harmonic voltage, coupled to the
main resonator of one-fourth wavelength coaxial type
as shown in Fig.7 [11]. A frequency range of the fifth
harmonics from 55 to 110MHz is covered in the flattop
acceleration system. In a power test, we successfully
generated the fifth-harmonic voltage waveform and
observed the flat-top voltage waveform as shown in
Fig.8 [12], by picking up an acceleration voltage signal
with an electrode capacitively coupled to the edge of a
dee electrode.
the microbeam formation. In order to realize the spatial
and targeting resolution of 1µm, which corresponds to
the size of a cell nucleus, a new lens focusing system
and a flat-top acceleration system have been developed.
An initial test of these systems has started and high
energy heavy ions like a 260MeV 20Ne7+ ion will be
available in 2003 as a first microbeam with a spot size
of 1µm.
CONCLUSIONS
ACKNOWLEDGMENTS
The authors would like to acknowledge all the staffs
of the cyclotron group and beam engineering laboratory
and also Dr. Y. Sudo for their continuous assistance
and support.
REFERENCES
FIGURE 7. The flat-top cavity mounted on the main
resonator of the TIARA AVF cyclotron.
FIGURE 8. The flat-top dee voltage waveform (upper)
and the fifth-harmonic one (lower) observed with the
pickup electrode at the fundamental frequency of
17.475MHz and the fundamental voltage of 25 kV in a
power test.
A heavy-ion microbeam with energy of hundreds
MeV is a significantly useful tool for research in
biology and biotechnology. In order to conform to the
research of the biofunction in cellular level for biology
or medicine, a single-ion hit system for the cyclotron
has been developed for the first time at TIARA. The
system can irradiate a countable number of ions with
the spatial and targeting resolution of 10µm using a
micro-aperture collimation system. The development is
based on the successful stabilization of the cyclotron
beam current, which allows easy and reliable tuning of
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