Download - Modelling of ion - driven deuterium retention in W O.V. Ogorodnikova in collaboration with

© Olga Ogorodnikova, 9th ITPA, Garching, May 7-9, 2007

Modelling of ion - driven deuterium retention in W

O.V. Ogorodnikova

in collaboration with

J. Roth and M. MayerMPI für Plasmaphysik, EURATOM Association,

Garching, Germany


Ion implantation and TDS

D retention in W has been studied in ion beam experiments: monoenergetic ion beam

E = 200 eV D+ to 3 keV D+

T = 300 K to 600 K

D inventory in W increases as a square root of fluence at RT => diffusion-limited trapping.

1021 1022 1x1023 1024 1x10251018

1019

1020

1021

W

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2

Incident fluence, D+/m2

Ogorodnikova O.V., Roth J., Mayer M., J. Nucl. Mater. 313-316 (2003) 469-477



D retention in W has been studied in ion beam experiments: monoenergetic ion beam

E = 200 eV D+ to 3 keV D+

T = 300 K to 600 K

D inventory in W increases as a square root of fluence at RT => diffusion-limited trapping.

Most of D are trapped in the bulk at high fluences.

1021 1022 1x1023 1024 1x10251018

1019

1020

1021

NRA< 6 m

W

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2


Ogorodnikova O.V., Roth J., Mayer M., J. Nucl. Mater. 313-316 (2003) 469-477


200 400 600 8000,00

0,40

0,80 experiments

1022 D/m2

1023 D/m2

200 eV D+, RT -> W

Des

orpt

ion

flux

, 1019

D/m

2 s

Temperature, K

1021 1022 1x1023 1024 1x10251018

1019

1020

1021

W

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2


TDS shows two peaks.Both peaks grow with fluence.Second peak (high-temperature) grows faster.



1021 1022 1x1023 1024 1x10251018

1019

1020

1021

W

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2


Pre-implantation with intermediate TDS increases the second peak.


200 400 600 800 10000,00

0,20

0,40

0,60

0,80

1,00

200 300 400 500 600 700 800 900 1000200 300 400 500 600 700 800 900 1000

200 eV D+ -> W

F=1022 D/m2, RT virgin W re-used W

Des

orpt

ion

flux

, 1019

D/m

2 s

Temperature, K


Modelling of D retention in PCW

trapping

Implantation, I0

Permeation, JL

Desorption, J0



trapping

Implantation, I0

Permeation, JL

Desorption, J0

Natural trapsIon-induced traps


Dislocations, Grain boundaries

Bubbles, Vacancies

200 400 600 8000,00

0,40

0,80 experiments

1022

D/m2

1023

D/m2

200 eV D+, RT -> W

Des

orpt

ion

flux

, 1019

D/m

2 s

Temperature, K

calculations

1021 1022 1x1023 1024 1x10251018

1019

1020

1021

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2



Diffusion model with two kinds of traps describes well experimental data.


200 400 600 8000,00

0,40

0,80 experiments

1022

D/m2

1023

D/m2

200 eV D+, RT -> W

Des

orpt

ion

flux

, 1019

D/m

2 s

Temperature, K

calculations


W(x,t)=Wm(1 – exp(-(1-r)I0xt/Wm))

Rate of defect production = f (initial traps, ion flux, ion energy, temperature)

0 1000 2000 3000 4000 5000 600010191020102110221023102410251026102710281029

vacancies

dislocations

intrinsic traps

F=1024 D/m2200 eV D+ -> W

ion-induced traps

Tra

p co

ncen

trat

ion,

m-3

x, nm

Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness

0.85 eV 1.45 eV


Dislocations, Grain boundaries

Bubbles, Vacancies

200 400 600 8000,00

0,40

0,80 experiments

1022

D/m2

1023

D/m2

200 eV D+, RT -> W

Des

orpt

ion

flux

, 1019

D/m

2 s

Temperature, K

calculations




0 1000 2000 3000 4000 5000 600010191020102110221023102410251026102710281029

vacancies

dislocations

intrinsic traps

F=1024 D/m2200 eV D+ -> W

ion-induced traps

Tra

p co

ncen

trat

ion,

m-3

x, nm






0 1000 2000 3000 4000 5000 600010191020102110221023102410251026102710281029

vacancies

dislocations

intrinsic traps

F=1024 D/m2200 eV D+ -> W

ion-induced traps

Tra

p co

ncen

trat

ion,

m-3

x, nm


200 400 600 800 10000,00

0,20

0,40

0,60

0,80

1,00

200 300 400 500 600 700 800 900 1000200 300 400 500 600 700 800 900 1000

200 eV D+ -> W

F=1022 D/m2, RT virgin W re-used W

Des

orpt

ion

flux

, 1019

D/m

2 s

Temperature, K

=10-2

=10-3

Rate of defect production is higher for pre-implantation with intermediate TDS



0 1000 2000 3000 4000 5000 600010191020102110221023102410251026102710281029

vacancies

dislocations

intrinsic traps

F=1024 D/m2200 eV D+ -> W

ion-induced traps

Tra

p co

ncen

trat

ion,

m-3

x, nm0 1000 2000 3000 4000 5000 6000

1023

1x1024

1025

1026

1027

200 eV D+ -> PCW

F=1024 D/m2

T=393 K

T=323 K

exp, Alimov [19] calculations

D c

once

ntra

tion,

D/m

3

x, nm



Which kinds of ion-induced defects of 1.45 eV can be produced by low energy ions? =>

- 200 eV cannot produce vacancies (Eth=860 eV)

- D self-aggregation in clusters due to stress field created by implanted deuterium



Why D agglomerates in clusters only near the implantation surface? =>

Because of stress field induced by ion implantation



D agglomeration in clusters and bubble growth

Tension and stress=>Displacement of W atom=>Di-vacancy=>Bubble growth

D traps by vacancy Several D trap by vacancy

=> =>

Tension and stress=>Dislocation (loop punching?)

Conditions for bubble formation:1) Saturation in D concentration2) Saturation in vacancies


Temperature effect

1021 1022 1x1023 1024 1x10251018

1019

1020

1021

W

200 eV, 380-470 K

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2


An increase of the temperature results in a decrease of D retention for recrystallized ´virgin´ PCW

At 400 K D retention increases with fluence faster than at RT


An increase of the temperature results in a decrease of D retentionfor recrystallized ´virgin´ PCW

Model describes well temperature dependence.

300 400 500 600 700

1018

1019

1020

1021

500 eV D+

200 eV D+ -> WRet

aine

d de

uter

ium

, D/m

2

Irradiation temperature, K

exp. TDS [present work] calculations [present work] TDS [Haazs], SCW

F=1024D/m2

D retention decreases with temperature for ´virgin´ W

Temperature effect

1021 1022 1x1023 1024 1x10251018

1019

1020

1021

200 eV, 380-470 K

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2





D retention decreases with temperature for ´virgin´ W.

Most of D are in the bulk.

Temperature effect

1021 1022 1x1023 1024 1x10251018

1019

1020

1021

200 eV, 380-470 K

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2


300 400 500 600 700 800

1018

1019

1020

1021

1022

3000 eV D+

500 eV D+

200 eV D+ -> WRet

aine

d de

uter

ium

, D/m

2


NRA up to 7 m [Alimov] exp. TDS [present work] calculations [present work] TDS [Haazs], SCW

F=1024D/m2


Lower D retention for 3 keV than for 200 eV at high fluences

Implantation energy effect

1021 1022 1x1023 1024 1x10251018

1019

1020

1021

3 keV, 373-400 K

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2




1021 1022 1x1023 1024 1x10251018

1019

1020

1021

D(x,t)

D=const

3 keV, 373-400 K

100%

Deu

teri

um r

etai

ned,

D/m

2


Increase of the stress field =>increase of the diffusion coefficient



1021 1022 1x1023 1024 1x10251018

1019

1020

1021

D(x,t)

D=const

3 keV, 373-400 K

100%

Deu

teri

um r

etai

ned,

D/m

2

Incident fluence, D+/m20 500 1000 1500 2000

0

10

20

F=1023 D/m2

F=1022 D/m2

F=1024 D/m2

D(x,t) at T=400 K

Dif

fusi

on c

oeff

icie

nt, 1

0-11 m

2 /s

x, nm

)/)()1(exp()/1(1(),( 0 mmm utxIrDDDtxD Increase of the stress field =>increase of the diffusion coefficient



1021 1022 1x1023 1024 1x10251018

1019

1020

1021

D(x,t)

D=const

3 keV, 373-400 K

100%

Deu

teri

um r

etai

ned,

D/m

2



0 10000 20000 300001023

1024

1025

1026

1027

1028

3 keV, 393 K

F=1024 D/m2

200 eV, RT

D c

once

ntra

tion,

m-3

x, nm

Calculated depth profiles


Ion-induced defects are produced during implantation by deuterium self-aggregation due to the stress field induced by the incident ion flux

• D retains in W in ion-induced defects and natural defects

•

• An increase of ion energy (or/and ion flux) results in an increase of the stress field in the implantation region. As a result the diffusion coefficient near the implantation region increases.

• Both no recrystallization and intermediate TDS (annealing up to 1200 K) increase the rate of defect production

Conclusions

The rate of ion-induced defect production depends on the energy of the incident ions, ion flux, sample temperature and initial trap concentration


Discussion



1021 1022 1x1023 1024 1x10251018

1019

1020

1021

3 keV, 373-400 K

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2






D retention decreases with temperature for ´virgin´ W.

D retention has a maximum for re-used W.

Implantation history effect

1021 1022 1x1023 1024 1x10251018

1019

1020

1021 re-used, 420 K

200 eV, 380-470 K

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2


300 400 500 6000

2

4

6

8

200 eV D+

500 eV D+

500 eV D+

re-used W

´virgin´ W

F=1023 D/m2Ret

enti

on, 1

020 D

/m2



D retention in the second peak increases with temperature for re-used W

300 400 500 600 700 800 9000,0

0,4

0,8

300 400 500 600 700 800 900

200 eV ->W

RT 473 K

electropolished,heated at 1573 K 3 hours

Des

orpt

ion

rate

, 1019

D/m

2 s

Temperature, K300 400 500 600 700 800 900

0,0

1,0

2,0

3,0

300 400 500 600 700 800 900

200 eV -> W as received F=1023 D/m2

RT 473 K

Des

orpt

ion

rate

, 1019

D/m

2 s

Temperature, K

Recrystallized W As-received W after multiple implantation


D retention in the second peak decreases with temperature for recrystallized W




Intermediate TDS increases the amount of initial high-temperature traps

Calculations using the higher rate of defect production are in a good agreement with experiments.

300 400 500 600 700 800 9000,0

0,4

0,8

300 400 500 600 700 800 900

200 eV ->W

RT 473 K

electropolished,heated at 1573 K 3 hours

Des

orpt

ion

rate

, 1019

D/m

2 s

Temperature, K300 400 500 600 700 800 900

0,0

1,0

2,0

3,0

300 400 500 600 700 800 900

200 eV -> W as received F=1023 D/m2

RT 473 K

Des

orpt

ion

rate

, 1019

D/m

2 s

Temperature, K



The increase of amount of initial traps increases the rate of deuterium cluster formation

Both intermediate TDS and no recrystallization increase the amount of initial traps



W: 3 keV D+, RT

400 600 800 10000.00

0.42

0.83

1.25

1.67

2.08

2.50

annealed W

3 keV -> W

1024D/m2, 373 K

5.641023(D/m)2

373 K, unannealed W

Des

orpt

ion

flux

, 1019

D/m

2 s

Temperature, K

Deuterium retention in W


Conditions for cluster formation in W

- Initial amount of defects

- Low solubility and diffusivity

- Low porosity

Acceleration of rate of cluster growth- High ion flux or/and ion energy

Conditions for cluster formation and bubble growth



1021 1022 1x1023 1024 1x10251018

1019

1020

1021

3 keV, 373-400 K

200 eV, RT100%

Deu

teri

um r

etai

ned,

D/m

2




Experiments

off-normal events & ELM´s• D retention in damage W n-irradiation

He-irradiation

• D retention at high implantation temperature (T=800 K - 1000 K) at different ion fluxes

R & D

Modelling

• Competition of erosion/diffusion

• Soret effect

• Maxwellian energy distribution

• Diffusion in tension field


Is D retention in W a problem for ITER ?


• Deposition of impurities, codeposition ?

• Damages in the near surface region by off-normal events


W as a divertor

Tplasma: 1-20 eVParticle flux : 1022 – 1024 /m2/sTw : ~1000 K





• Damaged by off-normal events near surface region


• Temperature of W can be important


W as a divertor


W as a FW

Tplasma: 1-5 eV ?

Particle flux : ~ 1020 /m2/sTw : ~500 K ?









W as a divertor


W as a FW

Tplasma: 1-5 eV ?


Bulk retention can be of concern









W as a divertor


W as a FW

Tplasma: 1-5 eV ?


Bulk retention can be of concern

n-irradiation – strong trapping in vacancies distributed over all W thickness


Talk outline• Experimental data

• Modelling of D retention in PCW

– Temperature effect

– Implantation history effect

– Ion energy effect