1 Deuterium retention and release in tungsten co- deposited layers G. De Temmerman a,b, and R.P....

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Deuterium retention and release in tungsten co-Deuterium retention and release in tungsten co-deposited layers deposited layers

G. De Temmermana,b, and R.P. Doernera

a Center for Energy Research, University of California at San Diego, USA

b Present address: EURATOM/UKAEA Fusion Association, Culham Science Centre, UK

G. De Temmerman 9th Int. workshop on H isotopes in FRM, June 2-3 2008, Salamanca, Spain

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Motivation Motivation

Co-deposition of material eroded from PFCs (C,Be,W) with tritium will contribute to the global tritium retention in ITER

Deuterium retention in Be co-deposited layers depends on Be deposition rate, energy of D particles and substrate temperature [1]

Although the erosion rate of tungsten will be much lower than that of Be/C, knowledge of the possible retention in codeposited W layers is required

Also, thermal release behaviour of hydrogen isotopes needs to be studied to determine the efficiency of fuel removal methods


1G. De Temmerman, Nucl. Fusion, in press

3G. De Temmerman 9th Int. workshop on H isotopes in FRM, June 2-3 2008, Salamanca, Spain

Ar+,D

W Atomss

Copper substrate

Tungsten target

Tungsten layers formed by DC-magnetron sputtering using a tungsten target

D2/Ar mixtures

Experimental (1/2)Experimental (1/2)

DC power supply, -400V on target

W target

Tsubstrate=RT-300C

P=20mTorr

Copper substrate

Deposition rate: QMB+weight measurement

Retention: TDS

Morphology: SEM


Cu substrate

B fieldW target

W target

ion flux: 2.5-3.5·1022 m2s-1

Te~ 6 eV

target bias –50/-150 V

Ttarget~ 600°C

Copper substrate

PISCES-B is a linear plasma device

Steady state plasma generated by an arc discharge initiated by a heated LaB6 cathode

Deposition rate

Retention: TDS

Morphology: SEM

Experimental (2/2)Experimental (2/2)

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Influence of the substrate temperature during deposition Influence of the substrate temperature during deposition Layers prepared with different substrate temperatures (15% Ar)

Layer thickness: 100-200nm (magnetron), 70-100nm (PISCES-B)

D/W decreases with increasing substrate temperature

D/W0.03 at room temperature



Influence of the tungsten deposition rate (1/3) Influence of the tungsten deposition rate (1/3) 2 ways of varying the deposition rate:

1. Vary the power to the magnetron (mainly change current to target, not voltage)

0 50 100 150 200 250

0.01

0.02

0.03

0.04

Power (W)D

/W

1

2

3

Dep

ositio

n rate (10

15 at.s-1)

50 100 150 2000

100

200

300

400

500

Power (W)

Vo

ltag

e (V

)

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Cu

rren

t (A)

Factor of 2 increase of deposition rate for 4 times the power

No clear effect on the retention

RT

2 ways of varying the deposition rate:

2. Vary the Ar fraction in the gas mixture

Influence of the tungsten deposition rate (2/3) Influence of the tungsten deposition rate (2/3)

0 10 20 30 40 50

0.01

0.1

Ar fraction (%)

D/W

1E-3

0.01

0.1

1

10

Dep

ositio

n rate (10

15 at.s-1)

2 orders of magnitude variation of deposition rate

Decrease of the retention with increasing deposition rate

RT



Influence of the tungsten deposition rate (3/3) Influence of the tungsten deposition rate (3/3) If we assume that the Ar fraction only affects the deposition rate (flux of D to the

surface higher than flux of W)

0.01 0.1 1

0.01

0.1

1

Experimental data linear fit

D/W

W deposition rate (1015 at.cm-2s-1)

General trend is a decrease of D retention for increasing deposition rate

39.0 drW

D


280)(60

600)(293

6).10(01.0

)220779

exp(107.5

1215

1.041.04.088.18

eVE

KT

scmatr

TrE

W

D

n

d

dn

Combined effect of deposition conditions Combined effect of deposition conditions Regression analysis of the data

Retention in co-deposited tungsten layers depends on the energy of the incident D particles, the W deposition rate and substrate temperature

For beryllium:

Tdi erE

Be

D 18013061.059.015.034.1510*94.2

1E-3 0.01 0.1 11E-3

0.01

0.1

1

Exp

erim

enta

l D/W

Predicted D/W


Layer morphology Layer morphology

15% Ar, RT

5% Ar, RT 5% Ar, RT, 45deg tilt

Dense and smooth layer formed with 15% Ar

At lower Ar concentration, formation of blister-like structures

large size distribution

0 1000 2000 3000 4000

2.0x1017

4.0x1017

6.0x1017

8.0x1017

1.0x1018

1.2x1018

1.4x1018

Temperature during deposition RT 100C 200C

Time (s)

Des

orpt

ion

flux

(m-2s-1

)

0

200

400

600

800

1000

Tem

perature (C)

TDS measurements made with thermocouple against the sample back

Deuterium thermal desorption Deuterium thermal desorption

2 distinct desorption stages at 200C and 800C


Desorption kinetics Desorption kinetics

0 1000 2000 3000 4000 5000 6000

5.0x1016

1.0x1017

1.5x1017

2.0x1017

2.5x1017

3.0x1017

3.5x1017

4.0x1017

Time (s)

Des

orpt

ion

flux

(m-2s-1

)

0

200

400

600

800

Tem

perature (C)

0 1000 2000 3000 4000 5000 6000

1x1018

2x1018

3x1018

4x1018

5x1018

6x1018

7x1018

8x1018

Time (s)D

esor

ptio

n flu

x (m

-2s-1

)

0

200

400

600

800

1000

Te

mp

era

ture

(C)

Comparison of the desorption kinetics of co-deposited W and Be layers

Temperature ramped up to 250C and then held for a given time

For Be: desorption stops at target temperature and restarts when temperature is ramped again

For W: exponential fall of desorption rate: diffusion limited process


W Be

Retention in co-deposited tungsten layers generally pretty low

D/W=0.15 has been measured for very low deposition rate (implantation of D in the layer ?). Similar observations in [2]

Retention decreases with increasing deposition rate and temperature

Retention increases with energy of the incident particles

Variation with deposition conditions similar to what is observed for Be

Deuterium desorption is a diffusion limited process: duration of the bakeout is important

Conclusions Conclusions

2K. Katayama, et al, Fus. Eng. Des., 82 (2007) 1645


1 Deuterium retention and release in tungsten co- deposited layers G. De Temmerman a,b, and R.P....

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