22P060-P
Development of Charge Stripping Plates for Tandem accelerators
金属表面を使ったタンデム加速のための荷電変換器開発	 
M. Sasao, S. Kitajima, A. Okamoto, K. Terai, M. Wada, T. Kenmotsu
笹尾真実子，北島純男，岡本敦，寺井健祐，和田元，剣持貴弘
Graduate school of Engineering, Tohoku University, Aoba,Sendai, Miyagi 980-8579, Japan
Graduate School of Engineering, Doshisha University, Kyotanabe,Kyoto, 610-0321, JapanA robust electron stripper for H- to H+ using a metal surface was developed for a compact tandem-type
DD or DT neutron generator of next generation. The experimental results showed that the conversion
efficiency, H+ fraction in the reflected particles, improved by surface polish up to the maximum valueof about 90%. Roughness parameters were measured for 2 samples of metal surface, polished andnon-polished, using a 3D laser-scanning microscope. The surface measurement indicated that there
was factor 4 improvement in the average roughness by polish.

1. Introduction
Compact and high intensity neutron
generators are strongly demanded in various
fields, such as application to in-situ calibrationof neutron diagnostics in nuclear fusion [1],security systems, land mining, and structural
evaluation of tankers or nuclear reactors. A
tandem acceleration concept has been proposed
for a DD or DT neutron generator [2-3]. In thisapproach, a D- beam is accelerated up to
several-hundreds keV toward a high voltage
stage for electron stripping, and the D+ beam
produced is re-accelerated and injected to a Dor T-target with almost doubled energy. This
type of accelerator requires a compact,mechanically robust electron stripping system,
which can endure high heat load.
As a new concept, a metal plate electron
stripper was tested, using 60 – 150 keV Hbeam [4]. The roughness of the metal surface
samples was measured by 3D Laser scanningmicroscope.
2. Measurement of the Conversion Efficiency
A layered stripping plate was proposed by
Terai et al. [4] for a compact neutron source.
In this system, a H- beam is injected onto a
metal surface with an oblique angle. In orderto test this concept, an experiment wasperformed using a test stand which wasdeveloped for an alpha particle diagnostics
method, Advanced Beam Source 103 (ABS103)[5-6]. The details of the experimental setup
were described in the reference 4.
The stripper was a pile of molybdenum
plates of 0.4 mm in thickness, 31mm wide and
25 in length to the beam direction. A set of 25
parallel plates separated by 0.2 mm in gap wastilted to the beam direction so that the beamincident angle to the plates was 89 degrees. The
reflected H+ ions were detected by the movablefaraday cup. One of strippers was fabricatedwith a molybdenum plate commerciallyavailable (non-polished). The other stripper
wasfabricatedwithhighly
polished
molybdenum (polished).
The beam from the stripper plate was firstly
charge-separated by an electric field separator,
and the beam profile was measured by amovable faraday cup.
The conversion efficiency from H- to H+ wasevaluated by comparing the measured H+ beam
current profile with the theoretical prediction ofoutgoing beam profile calculated using theTRIM code [7], where charge exchange
probability was not taken into account. The
calculated H+ beam profile normalized showed
the good agreement with the measured result.
The H+ beam current integrated over the beamprofile are shown in Fig. 1, as a function ofbeam energy. The experimental results of twocases, with the non-polished stripper (triangles)
and with the polished (circles) indicated that thereflected H+ current depends on the surface
condition. The H+ fraction in the reflectedparticles, that is the ratio of the H+ beam current

integrated over the beam profile to the resultsof TRIM calculation (squares), depends on theincident beam energy and the surface condition,with the maximum value of about 90% with thepolished surface.

High conversion efficiency, up to 90% wasobtained with a polished molybdenum surface.
Roughness parameters of the surface weremeasured using a 3D laser-scanning microscope.
The surface measurement indicated that a factor
4 improvement in average roughness results infactor 4 improvement in the conversion
efficiency.
Acknowledgments
This work was supported by Grant-in-Aid forPriorityArea442-16082101,
Ministry
Education, Science and Culture Japan, and inpart by Joint research program of the National
Institute for Fusion Science.
References
1. M. Sasao, et al., Rev. Sci. Instrum. 81,
10D329 (2010)
2. K. N. Leung, et al., AIP conf. Proc. 287, 368(1994)
3. J. Reijonen, F. Gicquel, S. K. Hahto, M.
King, T- P Lou and K-N Leung, D-D
Neutron Generator Development at LBNL,
Applied Radiation and Isotopes, 63, 757(2005), LBNL-56673.
4. K. Terai, et al., AIP Conference Proceedings,Vol. 1390 (2011)
5. M. Kikuchi, et al., Plasma and Fusion
Research SERIES,8,(2009),1539-1541]
6. N. Tanaka, et al., AIP Conference
Proceedings, 1097,(2009),443-448
7. SRIM & TRIM, http://www.srim.org/.

+Fig. 1 The H beam current integrated over thebeam profile divided by the initial H- beam current,with the non-polished stripper (triangles) and withthe polished stripper (circles). The squares indicate
the results of TRIM calculation.

3. Measurement of the Surface Roughness
The roughness parameters, the maximum(Rp) and minimum (Rv) height in a sample unit
area, the average roughness (Ra), skewness(Rsk), and Kurtosis (Rku) were measured for 2
samples of stripper molybdenum surface using
a 3D laser-scanning microscope (KEYENCE
VK-970). The results are shown in Table 1.
There was factor 4 difference in averageroughness between the 2 samples.
4. Conclusion
As a robust electron stripper for H- to H+, ametal surface stripper was proposed for acompact tandem-type DD or DT neutron
generator of next generation.
Table I.

Not Polished
Polished

Peak value
Rp[µm]
0.209
0.024

Measured Roughness

ValleyRv[µm]
0.207
0.037

AverageRa[µm]
0.053
0.012

Skewness
Rsk-0.147-0.336

KurtosisRku
3.56
2.06