10th itpa conference, avila, 7-10 jan. 2008 changes of deuterium retention properties on metals due...

10th ITPA conference, Avila, 7-10 Jan. 2008

Changes of Deuterium Retention Properties on Metals due to the Helium Irradiation or Impurity

Deposition

M.Tokitani 2), H. Iwakiri 1), N. Yoshida 1),S. Masuzaki 2), N. Ashikawa 2)

1) Kyushu University2) National Insititute for Fusion Science

Y

L

oshida

aboratoryY

L

oshida

aboratory

Research Institute for Applied Mechanics


Bombarding plasma facing components with helium causes changing of their

properties• He ash: divertor• He GDC: divertor & first wall• CX neutral: divertor & first wall

surface

mV-nHe

He Long range diffusion of He

He+

He V

I

Stable structure

Resistance

Instable

Long range diffusion of interstitial atoms

Aggregation of I

I‐loop formation

He ion, atom

Annihilation?


Effects of pre-irradiation of

heliumIncrease of helium bubble and dislocation loops densities causes increase of strongly trapped deuterium retention.

In a fixed helium bubble and dislocation loops densities case, deuterium trapping sites are changed depending on D fluence.

Lower fluence ： strongly trappedHigher fluence ： strong trap sites are

filled, and weakly trapped D increase.

300 400 500 600 700 800 9000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0x1018

1x1022D2+/m2

4x1021

1x1021

5x1020

No He 1x1022

Temperature (K)

Des

orp

tio

n R

ate

(D2/m

2s)

300 400 500 600 700 800 9000

2x1017

4x1017

6x1017

8x1017

1x1018

8x10 21He+/m 2

2x10 21He +/m 2

1x10 20He+/m 2

no He irr.

Des

orp

tio

n R

ate

(D2/m

2 s)

W8keV,1 ｘ 1021D2

+/m2 @300K

8keV, 2 ｘ 1021He+/m2 ＠ 300K


Bri

gh

t fi

eld

im

ages

Ne-GDH-GDHe-GDUn-irradiation

Dar

k fi

eld

im

ages

20nm

20nm

Specimens surfaces analysis Specimens surfaces analysis after exposed to three glow discharges (TEM)after exposed to three glow discharges (TEM)

Incident energy of ions are 200-300eV, and temperature of specimens were almost room temperature.

In contrast with the very heavy damages observed in the case of He-GD, these defects were not observed in the case of H-GD and Ne-GD.


Depth distribution of He bubblesDepth distribution of He bubblesH

e co

nce

ntr

atio

n [

a.u

.]

a) LHD He-GDC

(200eV ， 65h)

20 30 4010 500Depth [nm]

b) He+ irra. exp. (2keV-He+,1.0x1022)

TRIM-91TRIM-91(2keV-He(2keV-He++))

TRIM-91TRIM-91(200eV-He(200eV-He++))

Cross-sectional TEM observation by using FIB technique after He-GDC

Stereoscopic observation by TEM

10nm

HeHe(1)

(2)

(1) Deposition layer with about 10nm thick, very heavy damage such as large bubbles formation and surface roughening.

(2) In bulk, about 30nm thick, small helium bubbles (1-2nm) were formed in the matrix.

By using He-GDC, serious irradiation defects are formed in the deep range.By using He-GDC, serious irradiation defects are formed in the deep range.

Stainless steel specimen (SUS316L)


Un-exposed surfaceUn-exposed surface

Exposed surfaceExposed surface

m

m

[nm]653

00

10 0

10

550

The feature of Ne-GDCThe feature of Ne-GDC

(b) Ne-GDC

10nm

NeNe

Surface erosion of SUS316L after Ne-GDC as observed by AFM

Cross-sectional TEM observation by using FIB technique after Ne-GDC

Ne-GDC can remove the surface efficiently by a high sputtering yield.

A smooth surface and a no-defects internal structure can be obtained by using Ne-GDC.


He-GDC(65h) H-GDC(71.5h) Ne-GDC(55h)

Retention of Deuterium after GDCsRetention of Deuterium after GDCsAdditional deuterium irradiation to the specimen pre-exposed to three GDC were conducted in order to confirm the change of deuterium retention properties due to the GDCs.

300 350 400 450 500 5500.0

5.0x1017

1.0x1018

1.5x1018

2.0x1018 After He-GDC After H-GDC After Ne-GDC

D2 d

eso

rpti

on

rat

e [D

2/m2 s]

Temperature [K]

Fresh specimenFresh specimen(irradiated only D(irradiated only D++))

Total retention of deuterium becomes lower by performing GDCs.

►Reduction of oxidized film.

He-GDC showed highest deuterium retention among the three GDCs.

Ne-GDC showed lowest deuterium retention.

In H-GDC, most of the retained deuterium desorbs up to 370K.

SUS316L

2keV-D+

1.0x1022[D+/m2]

Room temp.


Y. Ueda reported in ICFRM 2007 that:Only 0.1% of He strongly affects H inward diffusion in W. Stress field around bubbles and reduction of effective diffusion area (diffusion through bubbles is unlikely) could reduce H diffusion.

In Ueda’s experiment, incident energy of deuterium and helium is 0.33keV and 1keV, respectively.In LHD glow discharge case, incident energy of deuterium and helium are 2keV and 200eV (glow discharge), respectively.

The difference of ranges of hydrogen isotopes and helium could be a key parameter.

Blistering suppression by simultaneous H and He ion beam irradiation

Mechanism of retention modification by He irradiation


Possible mechanism for the change of hydrogen isotope

retention propertiesStress field caused by bubbles and displacements and/or reduction of diffusion area could reduce hydrogen isotope transport in bulk.

Damaged regionRange of hydrogen isotopes

diffusion

diffusion

Deposition layer on the surface also a possible mechanism for reduction of hydrogen isotope release from the surface


Summary• Hydrogen isotope retention properties in metal are changed by helium irradiatio

n.

– Increase of hydrogen isotope retention is observed after helium ion beam (8 keV) irradiation.

– The influence of the GDCs on the deuterium retention was also examined. The sample exposed to He-GDC showed highest deuterium retention while Ne-GDC showed lowest.

• Stress field caused by bubbles and displacements and/or reduction of diffusion area due to helium irradiation could be a barrier for hydrogen isotope transport.

– Difference of ranges of hydrogen isotope and helium could be a key parameter.

• Estimation of incident He energy (ash, CX) is necessary

– Systematic experiment is necessary to confirm this assumption.

• Material, temperature, and so on

• After neon glow discharge, there is almost no damage in sample, and hydrogen retention substantially decreases.

– Neon glow discharge can be a tool for wall conditioning in ITER

10th itpa conference, avila, 7-10 jan. 2008 changes of deuterium retention properties on metals due...

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