Ion Generation via Interaction between Intense
Ultra-Short Laser Pulse and Solid Target for
Application to Cancer Therapy
Koji Matsukado1, Kenichi Kinoshita1, Zhong Li1, Hiroyuki Daido2, Yukio
Hayashi2, Satoshi Orimo2, Mitsuru Uesaka3, Koji Yoshii3, Takahiro
Watanabe3, Tomonao Hosokai3, Alexei Zhidkov3, Akira Noda4, Yoshihisa
Iwashita4, Toshiyuki Shirai4, Shu Nakamura4, Atsushi Yamazaki4, Akio
Morita4, Atsushi Ogata5, Yoshio Wada5, Tetsuo Kubota5, Fuminori Soga1,
Satoru Yamada1
National Institute of Radiological Sciences, 4-9-1 Anagawa Inage Chiba, Japan
Advanced Photon Research Center Kansai Research Establishment Japan Atomic Energy Research
Institute, 8-1 Umemi-dai Kizu Soraku Kyoto, Japan
3
Nuclear Engineering Research Laboratory School of Engineering, University of Tokyo, 22-2 Shiraneshirakata, Tokai, Naka, Ibaraki, Japan
4
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto, Japan
5
Graduate School of Advanced Sciences of Matter, Hiroshima University, 1-3-1 Kagami-yama
Higashi-Hiroshima, Japan
2
Abstract. We started a project to develop a very compact accelerator for cancer therapy. To
reduce the size of the system, we adopted a laser plasma ion source using a compact ultra-high
intensity laser. We have performed ion generation experiments in which laser parameters were
as follows: The wave length and the pulse duration were SOOnm and 50fs, respectively. Peak
power was 4-5TW. The laser pulse with normal incidence angle to the target was focused onto
the target with 15(im diameter giving power density of 3-4xl018W/cm2. Target foils were metals
(Ti, Al) and plastics (polypropylene, polyethylene) with the thicknesses of 4-100(im. We found
that the angular distribution of ions with an energy of -O.lMeV had a significant peak in the
backward and forward in respect to the laser incidence direction.
INTRODUCTION
In recent years, cancer therapies using charged particles such as a proton or a heavy
ion are remarked. The charged particle beams can kill only the cancer, because they
can localize the radiation dose to the tumor by presence of Bragg-peak. Especially
carbon beam is found to be effective for its large Radio Biological Effectiveness.
National Institute of Radiological Sciences (hereafter NIRS) has constructed a carbon
therapy facility named as HIMAC (Heavy Ion Medical Accelerator in Chiba) and has
been making a great score on the treatment of cancer using HIMAC. However,
HIMAC is too large system to be widely spread, in its geometrical size and in
construction cost.
CP647, Advanced Accelerator Concepts: Tenth Workshop, edited by C. E. Clayton and P. Muggli
© 2002 American Institute of Physics 0-7354-0102-0/02/$19.00
265
We started a project in which a very compact accelerator whose size would be 3m x
which was
a very
compact accelerator
size
be 3m we
x
10mWe
x started
10m fora project
cancer in
therapy
developed.
To reduce whose
the size
of would
the system,
10m x 10m
forplasma
cancer ion
therapy
was
developed.
To ultra-high
reduce the intensity
size of the
system,
we
adopted
a laser
source
using
a compact
laser.
It is well
adoptedthat
a laser
plasma ion
source
usingaa few
compact
intensity
laser. Itfrom
is well
known
high-energy
ions
of about
MeVultra-high
per nucleon
are emitted
the
known irradiated
that high-energy
ions of aboutlaser
a few
MeV per However,
nucleon are
theof
plasma
by an ultra-intense
pulse[l][2].
theemitted
energy from
spread
plasma
by an
laserthe
pulse[1][2].
However,
the reduce
energy the
spread
of
the
ions irradiated
is too broad
to ultra-intense
be injected into
accelerator.
If we can
energy
the
ions
is
too
broad
to
be
injected
into
the
accelerator.
If
we
can
reduce
the
energy
spread with a proper method, that is a phase rotation method[3], the laser plasma ion
spread can
withbe
a proper
that issystem
a phaseofrotation
method[3],
the laser plasma
ion
source
used asmethod,
an injector
the heavy
ion synchrotron.
The other
source
can
be
used
as
an
injector
system
of
the
heavy
ion
synchrotron.
The
other
elements of our accelerator system are the electron cooling ring and the compact ion
elements of developed
our accelerator
system
are the electron
coolingrespectively.
ring and the compact ion
synchrotron
by Kyoto
University
and the KEK,
synchrotron
developed
by
Kyoto
University
and
the
KEK,
respectively.
We have performed ion generation experiments at University of Tokyo. In the
We report,
have performed
generation
experiments
at and
University
of Tokyo. In the
present
the resultsion
of the
experiments
are shown
discussed.
present report, the results of the experiments are shown and discussed.
EXPERIMENTAL
SETUP
EXPERIMENTAL SETUP
Figure
1 shows the experimental setup. We used a 12TW table-top laser system of
Figure 1 shows the experimental setup. We used a 12TW table-top laser system of
University
the wave
wave length
lengthand
andthe
thepulse
pulseduration
durationwere
were
University of
of Tokyo.
Tokyo. In
In the
the experiment,
experiment, the
SOOnm
and
50fs,
respectively.
Peak
power
was
4-5TW.
The
laser
pulse
with
normal
800nm and 50fs, respectively. Peak power was 4-5TW. The laser pulse with normal
incidence
was
focused onto the target with 15|im diameter giving
incidence angle
angle to
to the
the target
target
was
18
2 focused onto the target with 15µm diameter giving
18W/cm 2. We found a pre-pulse at the time. Although we did
power
density
of
3-4x10
power density of 3-4x10 W/cm . We found a pre-pulse at the time. Although we did
not
of the
the pre-pulse,
pre-pulse, roughly
roughly speaking,
speaking, the
the time
time
not precisely
precisely measure
measure the
the property
property of
interval
the
pre-pulse
and
the main-pulse
main-pulse was
was about
about 5ns,
5ns, and
andthe
theintensity
intensity
interval between
between
the
pre-pulse
and
the
5
ratio
metals (Ti,
(Ti, Al)
Al) and
and plastics
plastics (polypropylene,
(polypropylene,
Target foils
foils were
were metals
ratio was
was 10"
10-5.. Target
polyethylene)
with
the
thicknesses
of
4-100|im.
We
used
CR39
track
detectorswhich
which
polyethylene) with the thicknesses of 4-100µm. We used CR39 track detectors
were
placed
at
~70mm
away
from
the
laser-target
interaction-point
to
observe
the
were placed at ~70mm
laser-target interaction-point to observe the
angular
distribution
of
ions.
Energy
of
ions
was
measured
with
the
range
filter
angular distribution of
ions was measured with the range filter ofof
O.Sjim
Al
foil.
During
the
measurements,
degree of
of vacuum
vacuum was
was kept
kept around
around
0.8µm Al foil. During the measurements, the degree
4
-4
10'
Torr.
10 Torr .
iff Ails
CR8S
TrMfc
Glass dosimeter
FIGURE 1.
FIGURE
1. Experimental
Experimentalsetup.
setup.
266
RESULTS AND
AND DISCUSSION
DISCUSSION
RESULTS
The
angular distribution
distribution of
of ion
ion emission
emission is
is shown
shown in
in Fig.2.
Fig.2. In
In the
the figure,
figure,we
wedefined
defined
The angular
aa direction
the laser
laser propagation
propagation as
as 00 degree
degree and
and represented
represented itit as
as "forward".
“forward”. The
The
direction of
of the
targets were
were Ti
Ti and
and polyethylene
polyethylene with
with 20|im
20µm and
and lOOjim
100µm thickness,
thickness, respectively.
respectively. The
The
targets
Ti
had peaks
peaks in
in both
both the
the forward
forward and
and the
the backward
backward directions.
directions.The
Thelatter
latter
Ti ion
ion emission
emission had
peak was
was larger
larger than
than that
that of
of the
the forward
forward direction.
direction. The
The results
results of
ofthe
theanalysis
analysisof
oftrucks
trucks
peak
with range
range filters
filters showed
showed that
that the
the maximum
maximum energy
energy of
of ions
ions was
was atatmost
most lOOkeV
100keVififthe
the
with
ions
were supposed
supposed to
to be
be protons.
protons.
ions were
According to
to the
the scaling
scaling law
law which
which associates
associates with
with the
the maximum
maximumenergy
energyof
ofion
ionand
and
According
the laser
laser intensity
intensity in
in I?l
Iλ22,, generation
generation of
of ions
ions with
with energy
energy of
of aa few
fewMeV
MeVper
pernucleon
nucleonisis
the
expected[1][2].
Our results
results do
do not
not follow
follow the
the scaling
scaling law
law for
for sub
sub pico-second
pico-second pulse
pulse
expected[l][2]. Our
laser
irradiated targets.
targets. Because
Because of
of the
the much
much shorter
shorter laser
laser pulse
pulse width
width than
than aa picopicolaser irradiated
second
or slightly
less, the
the acceleration
acceleration field
field for
for ions
ions lasts
lastsmuch
much shorter.
shorter.The
Theoptimum
optimum
second or
slightly less,
condition
of ion
ion acceleration
such as
as target
target thickness
thickness is
is much
much more
more crucial.
crucial. We
We should
should
condition of
acceleration such
also
point out
out an
an effect
effect of
of the
the pre-pulse.
pre-pulse. The
The intensity
intensity of
of the
the pre-pulse
pre-pulse was
was about
about
also point
13
W/cm
which is
is high
high enough
enough to
to generate
generate aa pre-formed
pre-formed plasma.
plasma. The
The main-pulse
main-pulse
10
1013
W/cm22 which
interacts with the
the pre-formed
pre-formed plasma
plasma after
after 5ns
5ns expansion.
expansion. The
The front
front of
of the
the expanding
expanding
preformed
preformed plasma is expected
expected to
to be
be 0.1-lmm
0.1-1mm from
from the
the original
original target
target surface.
surface. As
As aa
result, interaction of the
the main-pulse
main-pulse with
with the
the pre-formed
pre-formed plasma
plasma occurs
occurs before
before the
the
focusing position, resulting in
in reducing
reducing the
the laser
laser intensity
intensity on
on the
the plasma
plasma surface.
surface.The
The
16 17
2
~ W/cm
laser intensity seemed
seemed to
to be
be 10 16-17
W/cm2,, maximum
maximum ion
ion energy
energy of
of aa few
fewhundreds
hundreds
keV, where dominant mechanism
mechanism of
of the
the absorption
absorption of
of laser
laser energy
energy was
was the
the resonant
resonant
absorption. In this case, the ions
ions are mainly
mainly emitted
emitted backward[4].
backward[4].
,,CR39
107,
10S
It: 2 Op m
110*
0
20
40
60
80
100
120
140
Angle [dea.]
FIGURE
FIGURE 2.
2. Angular
Angular distribution
distribution of
of ion
ion emission
emission from
fromlaser
laserplasma.
plasma.
267
SUMMARY AND PROSPECTS
We started a national project to develop a very compact accelerator for cancer
therapy. To reduce the size of the system, we adopted a laser plasma ion source using
a compact ultra-high intensity laser.
We performed ion generation experiments at University of Tokyo and found that
the angular distribution of ions with an energy of -O.lMeV had a significant peak in
the backward and forward in respect to the laser incidence direction.
In 2002, we are planning to perform three experiments. One of them will be
performed at University of Tokyo using 12TW laser system that is mentioned above,
the other two will be performed at JAERI-Kansai using ITW and 100TW lasers. In
the experiments, the phase rotation method will be tested. For the experiments, we are
making preparations for detectors, for example, the electron spectrometer, the
Thomson parabola ion analyzer.
ACKNOWLEDGMENTS
The authors must thank Dr. F. Nishiyama of Hiroshima University, Prof. N.
Sakamoto and Dr. J. Karimata of Nara women's University, Dr. S. Nakamura of
Kyoto University, Prof. S. Okuda of Osaka Prefecture University for their corporation
and useful discussion on the calibration of detectors. We also thank TORAY
Industries Inc. for providing us a polypropylene foil as a target. These works ware
supported by the fund of Advanced Compact Accelerator Development Project from
the Ministry of Education, culture, sports, science and technology of Japan.
REFERENCES
1.
2.
3.
4.
E. L. Clark et.al., Phys. Rev. Lett. 85, pp.1654 (2000).
A. Maksimchuk et. al, Phys. Rev. Lett. 84, pp.4108 (2000).
A. Noda et. al., Beam Science and Technology 6, pp.21 (2001)
J. P. Friedberg et. al., Phys. Lett. 28, pp.795 (1972)
268