24P073-P
Study of sputtering and redeposition behavior of wall materials
by high energy particle loads tests
高熱粒子負荷試験による壁材料の損耗・再堆積測定に関する研究
Kenzo Ibano1, Yasushi Yamamoto2, and Satoshi Konishi1
伊庭野 健造1, 山本 靖2，小西 哲之1
1

Graduate school of Energy Science, Kyoto University
Gokasho, Uji-shi, Kyoto 611-0011, Japan京都大学エネルギー科学研究科 〒611-0011 京都府宇治市五ヶ庄
2
Faculty of Engineering Science, Kansai University
3-3-35, Yamate-cho, Suita-shi, Osaka 564-8680, Japan
関西大学システム理工学部 〒564-8680 大阪府吹田市山手町3-3-35
Experimental setup of hydrogen ion/neutral loads facility in Kyoto University is prepared. This device isdesigned to study the sputtering and redeposition behavior of the plasma facing materials, in particular,tungsten. Monte Carlo simulations for the sputtering and redeposition behavior were performed in order toensure the amounts of sputtered materials reaching to diagnostics. Calculation result indicates that the ion
beam flux produce well enough sputtered particles in order to determine its quantity.

1. Introduction
In the fusion devices, plasma facing materials arerequired to survive irradiations by ion and neutral
particle loads. Tungsten is expected to be a primary
option for the first wall of the nuclear fusion powerreactors such as DEMO [1, 2]. Although tungsten is
one of the most resistant materials to sputtering andshould not be sputtered by hydrogen ions withsmall energy, heavier particles, hydrogen ions andcharge exchange neutrals with energy of 1 keV andabove can cause sputtering from the tungsten
surface. Although irradiation to the first wall by
these particles should be avoided in the fusion
power reactors, it is more realistic to assume
presences of these particles. Because these ionsand neutrals cause many physical phenomena in thecomplex environment at the fusion devices, a
simple configuration ion/neutral beam device isuseful to study the plasma-wall interactions oftungsten. In particular, behavior of sputteredmaterial is difficult to observe by small energy ionsfrom linear plasma devices commonly used for thewall studies [3]. Thus an experiment is designed totest the behavior of tungsten wall samples by thehigh energy hydrogen ion beam. This paper
introduces experimental setup, preliminary result,and calculation result for this experiment.
2. Experimental
Experiments are performed in a main cylindricalvacuum chamber (length ~ 2 m, diameter ~ 1 m)
connected to an ion source chamber. In the ion
source chamber, hydrogen or deuterium arc plasma
is discharged at the DuoPIGatron ion source.

Produced positive ions are accelerated by theapplied 30 kV potential and transported to the mainchamber through a gate valve with a 60 cm
diameter. It is expected that some of ions areneutralized during its transportation. In the mainchamber, experimental setup is placed as shown in
Fig.1. In vacuo movable diagnostics of Faraday’s
cup and calorimeter are set in front of thisexperimental setup in order to evaluate the beam
property. Size of the beam is reduced to 30 cm
diameter by a molybdenum cover before reaching
to the sample holder. Target sample is a tungsten
tile of a square 50 mm on a side with a 1 mm
thickness, and tilted at 45o to the beam. This angle
can be changed to study the dependence of theangle of incidence. Sputtered materials are collectedby a collector plate or a Quartz Crystal
Microbalance (QCM.) It is possible that thisconfiguration slightly changed in future so that
QCM collects “thirdly” sputtered materials from theFig.1. Experimental setup

Fig.2. Monte Carlo calculation result of space distribution (left) and energy distribution (right) of tungsten
particles sputtered by the 30 keV H+ ions with 45 o of the angle of incidence.

collector. In addition, the experimental setup isdesigned to be able to apply a magnetic field inorder to observe the prompt redeposition.
A LaB6 filament is installed in the DuoPIGatron
ion source and tested with several shots. Optimizing
length and timing of the hydrogen gas injection,hydrogen arc plasma is maintained for a second
with ~ 60 A. Combined with the reference data, it isexpected that the incident flux reaches 1021 - 1022
/m2/s.
3. Simulations
Sputtering behavior is simulated by a Monte
Carlo simulation code; TRIM [4]. Calculated resultof distributions of sputtered tungsten particles areshown in Fig.2. As shown in this figure, it isexpected that there are two groups of sputteredparticles. One group is originating from a spot near
the incident point and having the cosine distribution.
Particles from this group contains small amounts ofparticles with a energy of > 100 eV. The secondary
particles ejected from Y > 0 are another group. It isexpected that the momentum of the incident
hydrogen ions transfer to the atoms over theincident point because of the 45 degree of the angleof incidence
In the experiment, tantalum tape is attached on
the collector surface in order to examine thesputtered tungsten particles. TRIM calculationshows that reflection coefficients are < 10 % forsputtered tungsten particles with < 100 eV ofenergies and 45o of the angle of incident. Thus, atleast 90 % of sputtered particles remain on thetantalum plate while tantalum is sputtered with
sputtering yields of around 0.01 - 0.05. In order tohave a monolayer of tungsten, it is estimated that~ 10 seconds of irradiation is enough. If a quartz
crystal microbalance is used to measure the weightof sputtered particles, assuming 0.1 % of sputteredparticles reach to the crystal surface, frequencychange of crystal reaches ~ 10 Hz/s which isenough for the weight determination.
5. Summary and future works
Experimental setups with preliminary result andsimulation result for the experiment of ion andneutral irradiation to the tungsten target areintroduced. Recently installed LaB6 filament
improves the arc performance of the ion source. It
is shown that the ion/neutral beam facility has acapability to measure the sputtering of tungsten byhydrogen particles.
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