Applications of accelerators for industries and medical uses
at the Wakasa Wan Energy Research Center
S. Hatori, T. Kurita, T. Inomata, S. Kakiuchi, Y. Ito, K. Yasuda, R. Ishigami,
M. Sasase, K. Takagi, M. Hatashita, K. Kume, S. Fukuda, G. Kagiya,
T. Hasegawa, N. Yokohama, K. Yamamoto, I. Maruyama, N. Ohtani,
S. Fukumoto and M. Kondo
The Wakasa Wan Energy Research Center, Fukui 914-0192, Japan
Abstract
At the Wakasa Wan Energy Research Center (WERC), we had constructed an accelerator system with
a 5 MV tandem accelerator and a 200 MeV proton synchrotron. The tandem machine has 5 beam lines for the MeV order
beam experiments. Also the tandem beam is injected to the synchrotron. The beam accelerated by the synchrotron is used
at three experimental beam lines. After the completion of the construction in 2000, we have been performing experiments
using the system for the ion beam analyses (RBS, ERDA, PIXE) and irradiations for the material and biological sciences.
In 2002, the study of the cancer therapy with a proton beam from the synchrotron was started. In this paper, the layout of
the accelerator facility, recent development for the accelerators and experiments will be reported.
tron and the medical beam line before the start of the
cancer therapy in June of 2002 will be describe at the
view point of the operation of the accelerator and beam
transport system.
INTRODUCTION
Construction of the accelerator system at The Wakasa
Wan Energy Research Center (WERC) was completed
in July of 2000. It consists of a 5 MeV Schenckel type
tandem accelerator and a 200 MeV proton synchrotron.
After tuning and commissioning of whole the system,
experimental researches using the accelerator beams
started in August 20001.
The MeV-ion beam from the tandem accelerator is
used for the irradiation for the improvement of the material and biological target and the ion-beam analyses such
as “particle induced X ray Emission analysis (PIXE)”,
“Rutherford Back Scattering analysis (RBS)”, “channeling RBS”, “Elastic Recoil Detection Analysis (ERDA)”,
“Nuclear Reaction Analysis (NRA)” and so on.
The tandem accelerator works as not only a supplier
for the experiments with MeV-energy beams but also an
injector for the synchrotron. One of the applications of
the beams from the synchrotron is the proton therapy.
Although the application for the therapy requires much
higher stability to the daily beam handling and certainty
to the long term operation than other experiments, our
combination of the tandem accelerator and synchrotron
seems to be rather challenging. In any case, steady operation of the whole system is crucial.
In this report, an introduction of the experiments with
the tandem accelerator beam will be given in the section
of “ACCELERATOR AND EXPERIMENTAL BEAM
LINES” first. The beam commissioning of the synchro-
ACCELERATOR AND EXPERIMENTAL
BEAM LINES
FIGURE 1 shows the schematic layout of the accelerator complex at WERC. The system consists of two ion
sources, a tandem accelerator, a synchrotron, two experimental rooms for the experiments using tandem beams
and two rooms for the irradiation of the beams from the
synchrotron.
Ion Source
One is a plasma sputter ion source2 called as "main
ion source" and another a charge-exchange ion source.
The former delivers highly intense pulsed H- or C- beams
for injection into the synchrotron through the tandem accelerator. The maximum peak current of the pulsed hydrogen beam amounts to 18 mA by the pulse discharge
with duration of 250 ms and repetition rate of 25 Hz.
The current of around 8 mA is enough for usual operation, i.e., injection into the synchrotron through the tandem accelerator.
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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cations of the material by ion implantation or damage by irradiation. The irradiation can be done under the circumstances of high (1000 K) or cold (100 300 K) temperature by using two stages.
For instance, SiC, a kind of semiconducIrradiation room 3
Tandem accelerator
tor is interesting in the application under
Terminal 5 MV
cancer therapy Irradiation
(nearly)
the severe circumstances of high temperaSchenckel rectifier
room4
parallel beam
ture and/or flux of radiation such as in
the space and fusion reactor. By using of
the beam line, the irradiation with a beam
High energy
was carried out. The defect in SiC was
experiment
observed by an electron microprobe6.
A second for the ion beam analysis.
m-PIXE
The line consists of a scattering chamber
with a five-axis target goniometer, two
Irradiation room 1
turn tables and several detectors, a E¥B
Synchrotron
Irradiation room 2
Accelerator room
velocity filter, a TOF counter and a gas
Ion beam analysis
p 200 MeV
counter for the particle identification.
12 6+
C , a 55 MeV/u
Transmission type ERDA have been apBeam experiment
plied to mass spectrometry of the hydroin air
gen isotopes in the storing alloy7 by usIon implantation
ing the irradiation beam line. From now
on, including such experiments, RBS,
PIXE, ERDA, RBS-triggered TOF mass
FIGURE 1 Schematic layout of WERC accelerator system
spectrometry and NRA experiments will
The latter provides DC He- and H- ions for the experi- be available. The beam line is now under development.
ments with the beam from the tandem accelerator. A com- AMS measurements will be able to be performed after
bination of a high intensity hot cathode source and an elec- future modification of the ion source, the injection systron-adder with Li vapour supplies 36 mA of He- ion to tem and beam current measurement. From the terminal
window of a third line, the beam can be extracted to the
the tandem accelerator.
air. By using three apertures, the beam size is reduced to
10 mm diameter. We can apply the beam to the bio-irraTandem Accelerator
diation or archeological matter3, 4.
200 keV m wave
ion source
He ion source
Main ion source
A beam from each ion source is pre-accelerated to 180
keV and injected to and accelerated by the tandem accelerator with a maximum terminal voltage of 5 MV. The
voltage is generated by Schenkel rectifier. In order to
enable transport and accelerate high intense beam from
the ion sources, the conveyor current amounts to about 1
mA. By using large capacitance for the terminal condenser, the ripple of the voltage when injection of pulse
beam is reduced to 2 kV at the terminal voltage of 5 MV.
It corresponds to energy dispersion of 4¥10-4 and less than
one-tenth of that of the RFQ-DTL system.
Experimental Area With Tandem Beam
The beam accelerated by the tandem accelerator of
the terminal voltage set at maximum 1.7 MV is transported
to the irradiation room 1. The room has two beam lines.
One is for the microanalysis experiments. The beam is
focused to the size of a few mm by using a set of magnetic-quadrupole doublet. In the terminal chamber, PIXE,
RBS and ERDA experiments are available3. The element
analyses of Japanese paper (washi) and shrimp have been
performed by PIXE4, 5. RBS measurement have been applied to structural analyses of semiconductors. Another
for the channeling-RBS experiment with a parallel beam
obtained by two micro-slits.
In the irradiation room 2, we can perform the experiments setting the terminal voltage at maximum 5 MV. We
have three beam lines in the room. One is for the modifi-
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Synchrotron
The proton beam from the tandem accelerator is injected to the synchrotron and then accelerated to 200 MeV.
The circumference of the synchrotron is 33.2 m. The
superperiodicity is 4. Each lattice has QF-D-QD-D and it
is operated in separate function style. Horizontal and vertical tunes are 1.75 and 0.85, respectively.
A period of the synchrotron consists of four modes,
i.e., injection, acceleration, extraction and return to injection. Accelerated beams are slowly extracted out of stable
region in the horizontal phase space by an RF knockout
system in 0.5 s (RF driven extraction8).
Experiments With Synchrotron Beam
In the irradiation room 4, using 200 MeV proton beams
from the synchrotron, we have performed measurements
of the radiation effects on materials such as rare-earth
magnets9 and electric devices with semiconductor. In this
area, the beam is extracted in the air. The development of
the dosimetry in the air is also done by comparison with
the measurements of proton-proton inelastic scattering and
gamma ray induced by 27Al(p, 3pn)24Na(b-)24Mg* reaction
and decay. Irradiation on biological targets are performed
for the improvement of species and the measurement of
the relative biological effectiveness (RBE) of the radiation. Also, development of the technique of making and
sity variation. Therefore, the application of the
synchrotron beam to the therapy strongly demands the highly intense beam with a good uniformity in the spill.
vertical line
horizontal line
X-ray CT for positioning
patient
scatterer and
wobbling magnet
Improvement of The Intensity
As mentioned already, the 200 MeV proton
beam from the synchrotron is obtained by repetition of injection, acceleration, extraction and
decceleration in each 2 s. The extraction current is sensitive to the effective injection and
acceleration. Pulsed beams from the ion source
are deflected by the electric steerer at the injection line to the tandem accelerator. Only 1/40
fraction of the pulses is injected to the tandem.
The steerer also regurates the duration of the
pulse. Proton beams with 10 MeV from the
tandem are injected to the synchrotron in the
multi-turn method because the tandem beam is
not so high to achieve single-turn injection. Pulsed beams
with the peak current of 5 mA and duration of 20 ms are
injected and stored up to 30 nC just before the start of the
acceleration.
Injected and stored protons are lost during the acceleration period, especially early in the period. One of the
reason of the loss is the betatron oscillation from the collective motion such as coupling by space charge effect.
The variations of the tunes were measured carefully and
the focusing and defocusing parameters were searched
not so as for the beam to be lost as possible. Also, in
order to expand the bunch and reduce the coupled motion
caused by the space charge effect, the second harmonic
voltage is added to the acceleration RF field. By these
tuning, the maximum beam current of 8 nA is achieved.
ridge filter, fine degrader and collimator
FIGURE 2 Overview of therapy beam lines
limiting irradiation field is performed simulating the dosimetry for the human body.
Cancer Therapy Beam Lines
FIGURE 2 shows the concept of the cancer therapy beam
lines in the irradiation room 3. The room has two beam
ports so as to irradiate the diseased part of the patient set
at a common isocenter in vertical and almost horizontal
(9.5 degrees) directions. In both ports, the irradiation area
transverse to the beam direction is made by scattering and
periodically swinging proton beams by use of a scatterers
and two wobbler magnets. Longitudinal area is obtained
by of a ridge filter spreading the width of the Bragg peak
in the human body (spread out Bragg peak; SOBP). Transverse and longitudinal area are limited by a collimator
and a bolus, respectively. The diseased part of the patient
is positioned at the isocenter by using of a X-ray CT and
a bed. Relation of the position between the CT and the
isocenter is known with an accuracy of a mm. Also, the
spacial displacement of the bed can be measured accurately10.
出射準備
SX
on
RFKO on
RFKオン
“Leak”
もれ
SYNCHROTRON TUNING
SX
on
出射準備
The beam used for the cancer therapy requires high
intensity, accurate control of the irradiation dose and the
constant intensity during the extraction period. During
the irradiation, the diseased part must be settled at the
isocenter. Highly intense beam reduces the duration of
the irradiation, i.e., the fixation of the patient. In our system, the irradiation field is made by swinging the beam
by the wobbling magnets. The constant intensity during
the irradiation is necessary for the homogeneous distribution of the dose in the irradiation field. The accurate
control of the dose is yielded by the precise measurement
of the dose, the homogeneous dose distribution and
quickly switching beams off. The precise dosimetry and
the beam switching depend on the statistical error in the
beam current monitor and the time structure in the inten-
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(a)
RFKオン
RFKO on
(b)
１ﾊﾟﾙｽ
64ﾊﾟﾙｽ平均
FIGURE 3 The time variation of the intensity
(a) is obtained by only knock-out RF sweep with constant
gain. In the case (b), the duration of the injected beam was
reduced to 12 ms and RF is amplitude-modulated and gain is
adjusted as a function of time. (a) shows the average intensity
of 20 pulses. In (b),upper shows the variation in one pulse.
Lower the average of the 64 pulses.
Adjustment of Beam Spill
Although so far the proton beam of 8 nA has been
achieved from the synchrotron, a limitation on the intensity is set at 3 - 4 nA for easy control of the beam spill.
FIGURE 3 shows the intensities of the beams as a function
of the lapse from the start of knockout-RF in action. After the ions are accelerated to the final energy, a separatrix,
which is a boundary between stable and unstable regions
in the transverse phase space, is formed by the excitation
of two sextupole magnets. Then the knockout-RF is excited for slow extraction. In the FIGURE 3 (a), which is for
the case that the frequency of RF is sweeped with a period of 1 ms during the extraction period as keeping its
gain constant, you can find a “leak” before the extraction
and ununiform time structure. The leak may be caused
by the lack of matching between the emittance of the beam
and separatrix size. The present system can adjust the
beam emittance in the injection by changing duration of
the beam pulse. Adjustment of the duration reduces the
intensity, however, no “leak” can be found in Figure 3
(b). Duration is reduce to 12 ms from 25 ms. Also, the
amplitude of the RF carrier is modulated so as to have a
band width of 50 kHz and modulation gain is adjusted as
a function of time in case of (b). Further tuning seems to
be needed for the beam spill to become better for higher
intensity.
magnets was measured by scanning a solid state detector
in two transverse directions in a water phantom. The medical irradiation requires the irradiation diameter of up to
100 mm. The measurement confirmed the uniformity of
the distribution within 2.5 % in the area for the 200 MeV
proton from the horizontal beam port. The longitudinal
distribution is adjusted by the range modulator of a combination of a ridge filter, polyethylene fine degraderes and
a bolus. The performance of the ridge filter was checked
by longitudinally scanning in the water phantom. The
measurement verified the control of the width of uniform
SOBP up to 60 mm. FIGURE 4 shows the dose distribution
in the irradiation field10.
CLINICAL TRIAL
The first treatment started in June of 2002. In this
fiscal year, Health, Labor and Welfare Ministry suggests
us to check the availability and the safety for the treatments of six patients. Clinical application for two patients with prostate cancer had been finished by the end
of July. The treatments were done with 200 MeV proton
from the horizontal port. Next four patients will be treated
in early three months of 200310. Our medical team has a
plan of application to the tumors in other part, for example, head and neck cancer by using another port and/or
various energy beams.
IRRADIATION FIELD
The distribution of the dose in the irradiation field made
by the scatterers of tungsten and a couple of wobbling
PROBLEMS IN USE OF SYSTEM
The application of the accelerator system is in so wide
region that it is difficult to share the system between the
experimental groups. The limitation of the available machine time yields being behind to the others in progress
of the research and/or reduction of the number of clinical
treatment. One of the solution may be the introduction of
another injector dedicated to the synchrotron.
SUMMARY
The accelerator system with a tandem accelerator and
a synchrotron was constructed and has been operated for
the various experiments at the Wakasa Wan Energy Research Center. The tandem accelerator is used for irradiation for the material and biological science. Also the
beam is applied for the ion beam analyses. The tandem
accelerator does not only supply MeV-ions for above experiments but also work as an injector of the synchrotron.
One of the purpose of the use of the tandem and synchrotron system is medical application. The application requires the highly intense beam with uniformity in the time
structure and under the accurate dose control. Careful
tuning of the beam operation by the system had been performed before the start of the cancer therapy in June of
2002. Two patients had already been treated and other
four cases will be scheduled in early three months of 2003.
Figure 4. Dose distributions (a) along the beam direction and
(b) in the transverse plane.
In (a), variety of ridge filters is succesful in changing the
width of SOBP from the Bragg peak for the mono-energy
proton (black circle), through 30 mm (black triangle), 40 mm
(white circle), 50 mm (white triangle) into 60 mm (black
square). In (b), in both directions of x (black) and y (white),
the uniformities are achieved within 2.5 % in the required
irradiation diameter of 100 mm.
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ACKNOWLEDGEMENT
Authors would like to appreciate careful, exact and
devoting machine operation of the accelerator operating
staff Mr. Y. Hayashi, Mr. M. Yamada, Mr. H. Yamada,
Mr. M. Dote, Mr. J. Mori, Mr. H. Hamaji and Mr. S.
Kimura.
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