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. NishimurabaGraduate	  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

MotivationØ Worldwide fusion program is now focused on
Tungsten (W) as plasma facing material indivertor. (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 insurface condition has not been investigated.

(i.e. change in boundary conditionfor hydrogen diffusion)Ø May impact tritium retention and safety.
Research purpose:
1. To determine how hydrogen transport / retention affected by surface meltingand 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 sphericalelectrodes	

Cu	  gasket	  3

Influence of surface melting ondeuterium permeation in tungsten	

4	Experimental
1. Prepare surface melt layer on W
Ø Nano second laser irradiation.

SampleW discthickness = 71 µm
φ = 30.8 mm

2. Characterization of surface melt and morphologyØ SEM (surface/cross section).
Ø Laser microscope (topological information).
30.8 mm	

3. D-only ion driven permeation experimentsØ HiFIT device.
Ø Temp: 500 ~ 1000 K
Laser meltedsurface	W
DDLaser	  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

8Depth, x	• From inverse thickness
dependence we confirm
diffusion limited transport.
• Indicates R << L.
(i.e. the controlling C isclose to the surface < 1µm)
• T ≥ 700 K, an increasein steady state flux for
melted surface (×2).
(i.e an increase in solute C)

WNormal surface (31 µm)(Data scaled by (31/71))

Melted surface (71 µm)

2R	

D700 K

615C

Permeation Flux (×10 D/m s)

C*C*J = −D≅D∂xL

×2	4
Normal surface (61 µm)(Data scaled by (61/71))

20400

500

600

700

800

900

1000

T (K)
7

Transient permeation spectra	
1.2

T = 570 K	
1Once traps filled at nearsurface, solute concentration
increases

Sum	
Normalized permeation flux	

0.8

D1	

0.6

C
0.4

D2	0.2Depth, x	0100	

1000	

Time (s)	
• At T = 570 K, good fit requires sumof 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	

2Diffusivity (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

10700 K

D2	Normal surface	

-14

101.2

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.	

-11000/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 throughthe bulk (since traps are saturable).
Ø The experiments clearly indicate that surface melting andmorphology changes due to heat loads does change the Dtransport 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-only1016l D+Ne照射：550K以上の温度領域で透過フラックス減少

D+Arl D+Ar照射：600K以上の温度領域で透過フラックス減少D+Ne101015Ø 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

14500

600700

800

900

1000

Temperature(K)12重水素のみの照射との比較	
D soluteconcentration	

10D +ND +A r

D+N
D
D+Ne/Arl 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 )1000l 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

1.00.8

T=550K

D +A rl 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 eD -only
0.4
0.20.0101001000	 

N orm alized	 perm eation	 flux

1.2

When permeation simultaneouswith 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？）DR

Lx

Solute D concentration	

窒素鵜の影響 （混合物)
DRLx

Ne/Arの影響 (スパタリング、Neの蓄積?)16

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