JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Development of Beam Generation and Irradiation
Technology for Electrostatic Accelerators
A. Yokoyama, S. Uno, A. Chiba, K. Yamada, Y. Saitoh,
Y. Ishii, T. Satoh, T. Ohkubo and T. Agematsu
Department of Advanced Radiation Technology, TARRI, JAEA
Cluster ion acceleration
The key points in accelerating cluster ions by means of a
tandem accelerator are both their cross-sections of collision
induced destruction and charge exchange in charge
exchanging gas. Therefore the cross sections were
measured for the carbon cluster ions (C 4, C 8, C 10), which
were frequently used in irradiation experiments at our
facility. Stripper gases of He, N 2 having different
molecular size and valence band electrons state were tested
to investigate a suitable gas for use in accelerating cluster
ions with a tandem accelerator. The cross sections are
deduced from a transmission probability through the tandem
accelerator as a function of the stripper gas density, and the
transmission probability can be written as
T = αe -σdχ (1 - e -σpχ ) • • • • (1)
where σ p and σ d are the production and destruction cross
sections respectively, and χ is the stripper gas density.
Figure 1 shows the transmission of C 10 as a function of
stripper gas density. From eq. (1), for high stripper gas
density the transmission should be proportional to e -σdχ .
Therefore, σ d can be taken directly form the slope of the
transmission curve at high gas density and σp can be
1)
determined by fitting eq. (1) to the total curve . As a
result, the destruction cross sections of Cn are proportional
to the cluster size, and those of helium are smaller than
those of nitrogen, whereas the production cross sections
seem to be no significant change on the cluster size and
stripper gas species. The results indicate helium gas
should be effective for cluster ion acceleration.
Transmission
0.1
0.01
0.001
0.0001
0 1x10 16
He
- +
C → C10
10
T=αe -σdχ (1-e -σpχ )
2x10 16
3x10 16
density (Atoms/cm 2 )
4x10 16
Fig. 1 Transmission of C 10 as the function of stripper
gas density.
Study of Faraday cup shapes for a fullerene beam
intensity distribution monitor
We are developing an ion beam intensity distribution
monitor using multi Faraday cup (MFC) 2) . Each FC unit
JAEA-Review 2010-065
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of MFC is required a high aspect ratio to measure beam
current accurately without a negative suppressor, because a
large number of secondary positive ions are produced by
fullerene collision and extracted by the electron-suppression
field. A depth and a bottom shape of the FC unit were
studied using 120 keV C 60 + beam with the 400 kV ion
implanter. The beam current was accurately measured
using 15 mm depth FC with both flat and oblique bottom, as
shown in Fig. 2.
Beam current (nA)
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Shape of FC
flat
oblique(45°)
0 5 10 15 20
FC depth (mm)
Fig. 2 The relationship between the measured beam
current and FC depth. The inside diameter of FC
unit is 3 mm. The accurately current was supposed
with dotted lines.
Emittance measurement using scintillator luminescence
induced by MeV proton beams
The emittance of the ion beams accelerated by the 3 MV
single-ended accelerator is measured using an emittance
monitor 3) . First, the emittance was estimated from the
numerically analyzed CCD camera images of luminescence
induced by proton beam injected into a scintillator, SiO2 thin plate. There was, however, a problem of an irradiation
damage of the scintillator. The YAG:Ce plate, 400 mm 2
and 0.2 mm thick, was tried instead of the SiO2. The
radiation resistance of the YAG:Ce scintillator was
demonstrated by measuring the two kinds of proton beam
induced luminescence intensity from several times proton
irradiation area or non-irradiation one. The experiment
also showed the luminescence had a good linearity to the
incident proton beam current. The brightness was
0.7 A m -2
sr -1
eV -1 as a preliminary study. The high
accuracy beam emittance will be studied using the improved
emittance monitor in the next year.
References
1) F. Ames et al., Nucl. Instrum. Meth. B 112 (1996) 64.
2) K. Yamada et al., JAEA Takasaki Ann. Rep. 2008
(2009) 168.
3) A. Chiba et al., TIARA Ann. Rep. 2002 (2003) 327.