大阪大学 Influence of surface melting or impurities (Ne, Ar) on

大阪大学
OSAKA UNIVERSITY
Influence of surface melting or impurities (Ne, Ar) on
deuterium permeation in tungsten
タングステン表面溶融及び不純物（Ne、Ar)が水素同位体の
透過へ与える影響
H.T. Leea, M. Ishidaa, Y. Uedaa
N. Tanakab, H. Nishimurab
aGraduate School of Engineering, Osaka University, Japan bIns>tute of Laser Engineering, Osaka University, Japan ダイバータ関係サブクラスター合同平成26年7月31日筑波大学 1
Motivation
Ø  Worldwide fusion program is now focused on
Tungsten (W) as plasma facing material in
divertor. (JET-ILW, ITER, DEMO)
W melt structure formed after TEXTOR edge plasma
Ø  Probability of some W melting and surface
morphological changes due to power loads.
Ø  N, Ne, or Ar are considered as extrinsic
impurities to reduce the local power load.
Ø  Hydrogen transport under such changes in
surface condition has not been investigated.
(i.e. change in boundary condition
for hydrogen diffusion)
Ø  May impact tritium retention and safety.
Research purpose:
1.  To determine how hydrogen transport / retention affected by surface melting
and N, Ne, or Ar impurities.
2.  To evaluate the magnitude of such changes on Tritium retention estimates.
2
Ion driven permeation apparatus
Faraday cup Ion beam mass -‐
analyzed for analysis Magnetic coils
Microwave
(2.45GHz)
ECR plasma
60° Gas inlet
Deflection coil
Q- mass
analyzer
Permeation experiment
IR Heater
(2kW)
Ion beam Energy : 1 keV ﬂux(D) : ~1020 m-‐2s-‐1 Species : D3+,D2+,D+ Heat
Thermo couple Three spherical
electrodes
Cu gasket 3
Influence of surface melting on
deuterium permeation in tungsten
4
Experimental
1.  Prepare surface melt layer on W
Ø  Nano second laser irradiation.
Sample
W disc
thickness = 71 µm
φ = 30.8 mm
2.  Characterization of surface melt and morphology
Ø  SEM (surface/cross section).
Ø  Laser microscope (topological information).
30.8 mm
3.  D-only ion driven permeation experiments
Ø  HiFIT device.
Ø  Temp: 500 ~ 1000 K
Laser melted
surface
W
D
D
Laser parameters Wavelength : 1064 nm Pulse width (FWHM) : 7 ns Beam spot: φ ~ 4 mm Intensity: ~600 mJ Laser power density: 7×1012 W/m2 5
Fine filamentary features and crater-like
dimples due to surface melting
10 µm
10 µm
6
Increase in steady state permeation at T≤ 700 K
Steady State condition:
L
∂C
8
Depth, x
•  From inverse thickness
dependence we confirm
diffusion limited transport.
•  Indicates R << L.
(i.e. the controlling C is
close to the surface < 1µm)
•  T ≥ 700 K, an increase
in steady state flux for
melted surface (×2).
(i.e an increase in solute C)
W
Normal surface (31 µm)
(Data scaled by (31/71))
Melted surface (71 µm)
2
R
D
700 K
6
15
C
Permeation Flux (×10 D/m s)
C*
C*
J = −D
≅D
∂x
L
×2
4
Normal surface (61 µm)
(Data scaled by (61/71))
2
0
400
500
600
700
800
900
1000
T (K)
7
Transient permeation spectra
1.2
T = 570 K
1
Once traps filled at near
surface, solute concentration
increases
Sum
Normalized permeation flux
0.8
D1
0.6
C
0.4
D2
0.2
Depth, x
0
100
1000
Time (s)
•  At T = 570 K, good fit requires sum
of two independent permeation
curves with two different diffusivities.
•  The two diffusivities interpreted
to be:
Effective diffusivities reflecting
trapping effects.
8
Difference only in the second diffusivity D2
between melted and normal specimen Frauenfelder’s value
“true” volume diffusivity
Melted surface
-11
D1 = (7±1×10-8) exp (-0.55±0.02 eV/kT)
D1
2
Diffusivity (m /s)
10
D2 = (1±1×10-9) exp (-0.40±0.05 eV/kT)
-12
10
D2 = (3±1×10-8) exp (-0.59±0.03 eV/kT)
-13
10
700 K
D2
Normal surface
-14
10
1.2
1.4
1.6
1.8
2.0
2.2
•  The higher D2 for melted
sample due to higher trap
filling ratio due to higher
solute D concentration.
-1
1000/T (K )
9
Summary of surface melt experiments
•  Surface melted layer on W permeation specimen and D-only
irradiation experiments performed.
•  T ≥ 700 K, an increase in steady state flux for melted surface (×2).
This indicates increase in solute concentration due to surface
melting.
•  Two diffusivities provide good fit to transient permeation spectra.
The higher solute concentration results in faster diffusion through
the bulk (since traps are saturable).
Ø  The experiments clearly indicate that surface melting and
morphology changes due to heat loads does change the D
transport but its impact is modest (×2).
Ø  Effect of mixed irradiation (D+X (X = He, N, Ne, Ar)) unknown for
melted layer.
10
重水素・Ne/Ar同時照射が
透過挙動に与える影響
11
Ne/Ar同時照射による
重水素定常透過フラックスへの影響
16
5x10
2
Permeation Flux(D/m s)
D-only
10
16
l  D+Ne照射：550K以上
の温度領域で透過フ
ラックス減少
D+Ar
l  D+Ar照射：600K以上
の温度領域で透過フ
ラックス減少
D+Ne
10
10
15
Ø  NeやArと同時照射す
ることで透過フラックス
が減少する傾向が見
られた
14
500
600
700
800
900
1000
Temperature(K)
12
重水素のみの照射との比較
D solute
concentration
10
D +N
D +A r
D+N
D
D+Ne/Ar
l  窒素によって透過フラッ
クスは増加
→表面にタングステンと窒
素の混合層が形成、表面
内部の重水素濃度が増加
1
N orm alized perm eation flux
*
(C /C at T < 780K )
D +N e
0.1
0.01
500
600
700
800
900
T em perature(K )
1000
l  Ne/Arとによって透過フ
ラックスは減少
→表面状態が変化し、表
面内部の重水素濃度が減
少
13
各照射におけるラグタイムの比較
*G. Federici, D. Holland, and R. Matera, J. Nucl. Mater. 233-237 (1996) 741-746.
透過フラックスが定常状態にな
るまでにかかる時間を重水素
のみ照射の場合と比較
1.0
0.8
T=550K
D +A r
l  D+Ar同時照射：重水素の
みの照射より定常状態に早
く達した
0.6
D +N e
D -only
0.4
0.2
0.0
10
100
1000
N orm alized perm eation flux
1.2
When permeation simultaneous
with sputtering* l  D+Ne同時照射：重水素の
みの照射より定常状態に達
するまで時間を要した
→同じ希ガスの照射だが結
果に違いが現れた
10000
Tim e(s)
14
D+Ne/Ar　透過実験のまとめ
l  D+Ne、D+Ar照射を行い、Ne/Arが重水素の透過に与える影
響を調べた。
l  Ne/Arとの同時照射で、大部分の温度領域で透過フラックスが
減少する結果となった。これは、Wの表面内部の重水素濃度
が減少したことによると考えられる。
l  透過フラックスが定常状態になるまでにかかる時間は、D+Ar
照射では重水素のみの照射より短かったが、D+Neではより長
い時間がかかった。Neの照射によってスパッタリング以外に拡
散に影響をおよぼす現象がある可能性が考えられる。
15
まとめ
A) 表面溶融
B) Ne/Ar同時照射
C*
Solute D concentration
C*
表面溶融 (メカニズム？）
D
R
L
x
Solute D concentration
窒素鵜の影響　（混合物)
D
R
L
x
Ne/Arの影響 (スパタリング、Neの蓄積?)
16
17

Download Report