24P079-P
The Effect of Mixed Plasma Irradiation on the Surface Structure of Tungsten
混合プラズマ照射がタングステン表面構造に与える影響
Hiroyuki Okuda, Toshitaka Kawai, Yusuke Ohtsuka, Yoshio Ueda, Naoaki Yoshida
奥田啓之 a, 河合俊昇 a, 大塚裕介 a, 上田良夫 a, 吉田直亮 b
a Graduate School of Engineering Osaka University
2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
大阪大学工学研究科〒565-0871大阪府吹田市山田丘2-1
b Research Institute for Applied Mechanics Kyushu University
6-1, Kasugakoen, Kasuga, Fukuoka 816-8580, Japan
九州大学応用力学研究所〒816-8580福岡県春日市春日公園6-1
The effects of argon or neon plasma which works as radiative cooling gas to tungsten surface structure
should be investigated. In this study, pure plasma irradiations or mixture plasma irradiation with He, Ne,and Ar to tungsten are performed in an ECR plasma device. The surface modification by He plasmas andthe effects of Ar and Ne on He induced morphology (nano-structure) observed by a scanning electron
microscope (SEM) or a transmission electron microscope (TEM).

1. Introduction
Tungsten is one of the candidates for divertermaterials in ITER because tungsten has highmelting point and low sputtering yield. However,there is a concern such that helium plasma
generated by D-T reaction makes surface damage
on tungsten. Therefore, the influence of helium
plasma on tungsten has been investigated. In
particular, at high temperature and high ion
energy, helium exposure on tungsten forms
nanostructure-sized fibrous structure whichcontains the helium bubble [1].
In addition to the effects of helium, argon orneon plasma possibly affects surface morphologies
of tungsten. Argon and neon have an important rolein nuclear fusion reactors such that they are
expected to work as radiative cooling gas indiverter plasmas. In this study, the effects of argon
and neon ion irradiation on the tungsten
nanostructure induced by helium plasma irradiation
are studied.
2. Experiments
The experimental device is called LaPlex (Laserand Plasma exposure device). Steady state highdensity plasmas are produced by electron cyclotron
resonance (ECR) discharge by 2.45 GHz
microwave. Tungsten samples size is 10mm squareand 1mm thickness, and their surface are polished
to a mirror finish. The sample holder is electricallyisolated from the vacuum chamber and can bebiased (~150V) to control the incident ion energy tothe tungsten surface. The surface temperature oftungsten is measured by a radiation thermometer,
and the surface morphology and microstructure areobserved by SEM or TEM.
3. Analysis method
At high temperatures (>1200K) and high ion
energies (>100eV), the surface color of sample
exposed to helium was totally black visually after
the exposure. The exposure time, ion energy, andtemperature were 3600s, 150eV, and 1300K
respectively, The SEM micrograph of the samples
showed the fibrous structure about 500 nm inthickness.
The mixed plasma irradiation is expected tochange the tungsten surface because argon and neon
have higher sputtering yield than that of helium.
Among several parameters, ion energy is a more
important parameter because the sputtering yield oftungsten is increased rapidly with increasing theincident ion energy. This parameter is expected tochange the morphology of tungsten surface.
Similarly, there is possibility for ion density andexposure time to change the tungsten surface. We
investigate the dependency of these parameters ontungsten surface and formation process of tungsten
nanostructure.
References[1] W. Sakaguchi, S. Kajita, N. Ohno, and M. Takagi:
Journal of Nuclear Materials 390–391 (2009)
1149–1152.