Influence of Crystallographic Orientation on Helium Bubble and

Influence of Crystallographic Orientation
on Bubble and Fuzz Structure Formation
in Tungsten Exposed to Helium Plasma
. Ohno, Y. Hirahata, S. Kajita, T. Saeki, M. Yamagiwa
agoya University, Japan
. Yoshihara, N. Yoshida
yushu University, Japan
M. Tokitani
IFS, Japan
19th International Conference on
Plasma Surface Interactions
May 24-28 2008, San Diego, USA
1
Background and Purpose
NAGDIS
Background
- Bubble and nanostructure formation (fuzz) in W caused by
He plasma exposure
→ bubble and nanostructure formation reduces the
durability to heat load, leading to the release of great
amount of tungsten impurity.
- Understanding the formation mechanism is one of key issues
in case of application of W as plasma-facing components in
fusion devices. However, the mechanism of the nanostructure
formation has been not fully understood yet.
Purpose
-Investigate the effect of Crystal Orientation on bubble and
nanostructure formation especially at initial phase (transition
from bubble to protrusion) by using ITER reference W (Recrystallized), Single Crystal W (100), (110)
Summary of bubble and fuzz formation condition
NAGDIS
NAGDIS
•Closed markers
with nanostructure
•Open markers
without nanostructure
Surface Temp: 1000 K < T < 2000 K
Ion Incident Energy>20 eV
Kajita et al. NF2009
[4] M. Baldwin NF (2008).
[7] W. Sakaguchi JNM (2009)
[8] S. Kajita, NF (2007).
[9] S. Kajita, NF (2009).
[11] S. Kajita, J. Appl. Phys. (2006).
[12] W. Sakaguchi, Proc. 18th Int. Toki Conf. (2008).
[13] D. Nishijima, JNM (2004).
[14] D. Nishijima, JNM (2003).
[15] D. Nishijima, NF (2005).
3
Summary of bubble and fuzz formation condition
NAGDIS
NAGDIS
Dr. Iwakiri
(Kyusyu univ.)
•Closed markers
with nanostructure
•open markers
without nanostructure
Surface Temp: 1000 K < T < 2000 K
Ion Incident Energy>20 eV
Kajita et al. NF2009
[4] M. Baldwin NF (2008).
[7] W. Sakaguchi JNM (2009)
[8] S. Kajita, NF (2007).
[9] S. Kajita, NF (2009).
[11] S. Kajita, J. Appl. Phys. (2006).
[12] W. Sakaguchi, Proc. 18th Int. Toki Conf. (2008).
[13] D. Nishijima, JNM (2004).
[14] D. Nishijima, JNM (2003).
[15] D. Nishijima, NF (2005).
4
Development of
W nanostructure
NAGDIS
PM-W 1400K 50eV-He plasma
Bubble
Pinhole
Protrusions
Swelling
&Digging
NanoStructure
(Fuzz)
TEM
(FIB)
SEM
S. Kajita, et al. NF20009
5
Initial phase of W nanostructure formation
PM-W 1400K, 50eV-He plasma, 6x1024He+/m2 (375 s)
NAGDIS
NAGDIS
„ Bubbles (~ 50nm) in the swelling and under the surface (100nm)
„ Shape of bubble：sphere
100nm
100nm
Initial phase of W nanostructure formation
PM-W 1400K, 50eV-He plasma, 6x1024He+/m2 (375 s)
NAGDIS
NAGDIS
„ Bubbles (~ 50nm) in the swelling and under the surface (100nm)
„ Shape of bubble：sphere
Bubbles??
100nm
100nm
Difference in bubble and fuzz formation for each grain
NAGDIS
NAGDIS
26
+
2
ITER reference-W 1800K 30eV-He plasma 7.2x10 He /m (36000 s)
Large grains grow due to high surface temperature
500
500μm
μm
- Surface modification is quite
different for each grain
- black region -- flat
terrace-like structure
- white region – bumpy
50
50μm
μm
5μm
55μm
5μm
μm
8
Grain with wider terrace has few protrusions
NAGDIS
NAGDIS
ITER reference-W 1800K 30eV-He plasma 7.2x1026He+/m2 (36000 s)
55μm
μm
55μm
μm
55μm
μm
55μm
μm
TEM observation of boundary between grains
NAGDIS
with terraces and protrusions NAGDIS
ITER reference-W 1800K 30eV-He plasma 7.2x1026He+/m2 (36000 s)
Sample Area
milled by FIB
10μm
10μm
TEM observation of boundary between grains
with terrace and protrusions (2) NAGDIS
NAGDIS
„ In the grain having the terrace, many bubbles, but no protrusions
„ In the grain with protrusions, the surface goes down 600nm
from original surface
„ The depth of the hole becomes deeper along grain boundary
Development of
“terrace” structure
development of
nano-structure
projection
f ac e
original sur
face
retreat of sur
G.B.
Area milled by FIB
10μm
10μm
＜１１３＞
＜１１３＞
1μm
Bubble shape in grain having few protrusions
NAGDIS
ITER reference-W 1800K 30eV 7.2x1026He+/m2
Polygon shape bubbles with a diameter above 300nm
surrounded by (110) surface
→ Gas pressure inside bubbles is relatively small
→ Few flaking
→ Few pinholes on the surface
101
200nm
200nm
He plasma exposure to single crystal W
NAGDIS
Specimens: Single crystal W (0.5mm thickness)
(110) : closed-packed plane
W(bcc)
→ split plane
(100) :
- Cutting disks from single crystal
tungsten rods
- Mirror finish by mechanical polishing
- Remove disordered surface layer by
(100)
using electrolytic polisher
(110)
XRD (100)
He plasma
(100)
(110)
PM-W
13
Surface modification on single crystal W(100)
NAGDIS
1600K 64eV 1.0x1025He+/m2
- Slow growth of protrusions
- Protrusion starts to grow
at edge of pinhole (burr)
- Once a protrusion appears,
it grows rapidly.
Surface modification on single crystal W(110)
NAGDIS
1600K 64eV 1.0x1025He+/m2
Tilt 45º
1μm
1μm
1μm
1μm
Tilt 60º
-Strange wavy structure
to be extended in one direction
like a mountain range
-Fewer pinholes
-Fewer protrusions
1μm
1μm
Surface modification on single crystal W(110)
NAGDIS
1600K 64eV 1.0x1025He+/m2
200nm
200nm
200nm
200nm
<001>
Sample
Sample area
area by
by FIB
FIB
1μm
- Cross section of wavy structure is almost
triangle having planes with (010) and (001)
- Wavy structure expands along (001)
- Protrusion formation is very slow
- It takes a time for (110) surface
to be changed to (100)
Summary -1
Conclusions
NAGDIS
NAGDIS
- Investigate the effect of crystallographic orientation on formation
of bubble and nanostructure
At re-crystallized ITER reference W
crystal grains with terrace and flat structure (113) have fewer
protrusions even they have a lot of bubbles formed under the
surface. Typical shape of bubbles is polygon.
At the single crystal W (100)
a protrusion starts to grow from edges of flaked bubbles.
At the single crystal W (110)
strange wavy structure having surfaces with (010) and (001) was
formed. Fewer pinholes → Fewer protrusions → Slow
nanostructure formation.
W(110), (100), (113) slow growth, but fast growth grain??
Future works
Re-crystallized W with large grain by only heating → Orientation of
all grains is analyzed before He plasma exposure.
17
NAGDIS
Appendix
18
SIM images of terrace region sputtered by FIB
NAGDIS
many bubbles under the surface
30度傾斜
30度傾斜
He flux and fluence in ITER
NAGDIS
ITPA presentation by Y. Ueda
20
He bubble and hole formation at bulky W (2)
NAGDIS
Threshold of incident ion energy as low as 6 eV
D. Nishijima, M. Y.Ye, N. Ohno, S. Takamura
Journal of Nuclear Materials, Vol.313-316, 2003, pp.97-101
21
He bubble and hole formation at bulky W (3)
NAGDIS
Threshold of surface temperature and fluence
Hole Formation
Nano Structure
22
Orientation of grains
A:001
C:111
100μm
100μm
B:101
Results
B:（101）
A:（001）
0.5μm
C:（111）
0.5μm
0.5μm
SCW(100)
SCW(110)
PM
5μｍ
5μｍ
5μｍ
2μｍ
2μｍ
2μｍ
SEM micrograph
照射時間300s
入射イオンエネルギー69.8eV
フラックス1.9×1022m-2s-1
フルエンス0.6×1025m-2
試料温度 1568 [K]
照射時間720s
入射イオンエネルギー64.4eV
フラックス2.0×1022m-2s-1
フルエンス1×1025m-2
照射時間1080s
入射イオンエネルギー66.4eV
フラックス1.5×1022m-2s-1
フルエンス1.6×1025m-2
試料温度 1599 [K]
試料温度 1519 [K]
(100)
2μｍ 2μｍ
試料温度 1554 [K]
2μｍ
試料温度 1598 [K]
2μｍ
試料温度 1483 [K]
(110)
2μｍ
試料温度 1544 [K]
2μｍ 2μｍ
試料温度 1579 [K]
2μｍ 2μｍ
試料温度 1499 [K]
PM
2μｍ 2μｍ
2μｍ 2μｍ
2μｍ 2μｍ