MoD-PMI 2019
June 18th – 20th at NIFS

Presentation No. O-16

Development of functional material
for deuterium permeation observation
under divertor plasma exposures
T. Takimotoa, N. Ashikawab,c, D. Morid, K. Katayamad, V. Rohdee,
Y. Matsumuraa, A. Tonegawaa, K.N. Satof, and K. Kawamuraa
aTokai University (Japan), bNIFS (Japan), cSOKENDAI (Japan),dKyushu University (Japan), eIPP (Germany), fTokyo University of Science (Japan)

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Table of Contents◆ Background & Motivation
 Observation of D permeation amount in PFCs

◆ New method to observe D permeation amount Concept of new method
 Design of W-Pd-Ti sample◆ Plasma exposures in the linear plasma device
 Experimental apparatus – the linear plasma device TPDsheet-U Detection of D amount on the sample surface◆ Summary & Future Plans
2

Table of Contents◆ Background & Motivation
 Observation of D permeation amount in PFCs

◆ New method to observe D permeation amount Concept of new method
 Design of W-Pd-Ti sample◆ Plasma exposures in the linear plasma device
 Experimental apparatus – the linear plasma device TPDsheet-U Detection of D amount on the sample surface◆ Summary & Future Plans
3Background➢ In DEMO, control of tritium (T) amounts is critical issue because of its
radioactivity and necessity of reuse.
➢ Although hydrogen isotopes diffuse into plasma-facing components (PFCs)
under high heat flux and particle flux, its amounts have not been measured.
➢ Therefore, it is necessary to directly evaluate the retention and permeation
amount of hydrogen isotopes in PFCs.
High temperature region

desorption
D
D

D
D

D

plasmaD
D

permeation
D
D

D
D

DD

D

D
D

PFM
During plasma exposure➢ During plasma exposure, hydrogenisotopes in plasma-facing materials
DD(PFM) are desorbed or permeates.
D➢ After plasma exposure, it can beobserved retention of hydrogen
DPFM
isotopes in materials by TDS, andAfter plasma exposure so on.
retention

4

Background⚫ Hydrogen isotope permeation has been investigatedin laboratory-scale plasma devices and fusion
devices by using quadrupole mass analyzer (QMA)
installed behind a membrane.
For example: I. Takagi et al., J. Nucl. Mater. 415 (2011) S692-S695.
H.S. Zhou, Plasma and Fusion Research, 8 (2013) 2402065.

⚫ However, QMA method is difficult to perform atPFCs under high heat flux and particle flux such asHightemperature
regionretention
desorption
divertorregions due to limited spaces, strong
DD
permeation
DD
D
magnetic
fields, high heat loads, and so on.
DDDD
plasma
D
D

D
D

D
D

D

D
D

PFM
During plasma exposure

D⚫ It is required
to develop a new method to measure
D amounts of permeation in PFCs.
DPFM
After plasma exposure
5Motivation & Aim
There is no precedent for direct evaluation of hydrogen permeation in PFCs
under high flux plasma exposures in fusion devices.
⚫ A new method have been proposed that titanium (Ti) and palladium (Pd) are
combined with tungsten (W) to store permeated deuterium (D).
⚫ It is planed that hydrogen isotopes amount of permeation in PFCs ofcurrent fusion devices such as ASDEX-U is measured by this method.
⚫ It is expected that characteristics of hydrogen isotopes obtained by themethod will contribute to T handling in DEMO.

In this work, W-Pd-Ti combined samples has been developed andimproved in order to use in tokamaks.
6

Table of Contents◆ Background & Motivation
 Observation of D permeation amount in PFCs

◆ New method to observe D permeation amount Concept of new method
 Design of W-Pd-Ti sample◆ Plasma exposures in the linear plasma device
 Experimental apparatus – the linear plasma device TPDsheet-U Detection of D amount on the sample surface◆ Summary & Future Plans
7

Concept of new method
It has been considered that Ti and Pd are combined with W to store the permeated D.

⚫ In order to store permeated D, we used Ti which isa hydrogen storage metal.

Pd⚫ Ti is installed behind W.

desorption
DDD
DDplasma
DDpermeation
DD
D

DD

DD

DDDW

D

⚫ Pd enhances the D transport from W to Ti.
⚫ Pd is used at contact surfaces of W and Ti as acatalyst.

Ti

During plasma exposure

8Concept of new method
It has been considered that Ti and Pd are combined with W to store the permeated D.

➢ Whenmolecules
diffuseinto⚫ In order to store
permeatedD, we usedTi whichismaterials,
they must be dissociateda hydrogen storage
metal.
Pdat the surface.
⚫ Ti is installed behind W.
⚫desorption
Dissociative
energies of hydrogenD➢ A dissociation needs high energy.
DpermeationDD
molecules
forthediffusion
intoD
DD⚫ Pd enhances the D transport from W to Ti.
materials arelowerthan most ofD
Dplasma⚫ Pd is used at contact surfaces of W and Ti as ametals. D D
DFor example: E. B. Maxted et al., J. Chem.
Soc. 1959,catalyst.
3130.
DDH. Nakatsuji
et al., J. Am. Chem. Soc. 1985, 107, 26.
DDDW D TiDuringexposure⚫ Duetoplasma
Pd layer,
it is expected thatD permeates to base materials as
atoms without recombination.
⚫ Pd is one material of the hydrogenpermselective membranes.

9Concept of new method
It has been considered that Ti and Pd are combined with W to store the permeated D.

⚫ In order to store permeated D, we used Ti which isa hydrogen storage metal.

Pd⚫ Ti is installed behind W.

desorption
D
D

D
D

D

plasmaD
D

permeation
D

D
D

D
D

D
D

DDDW

DTi

During plasma exposure⚫ Pd enhances the D transport from W to Ti.
⚫ Pd is used at contact surfaces of W and Ti as acatalyst.

⚫ W is a candidate of PFMs.

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Concept of new method
It has been considered that Ti and Pd are combined with W to store the permeated D.

Pddesorption
D
D

D
D

D

plasmaD
Dpermeation
D

D
D

D
D

D
D

D
D

D

W

D

Ti

During plasma exposure⚫ From these reasons, the combination of thematerials was selected.
⚫ In the previous study, D amounts of permeation
had been observed as D retention in Ti. [1]⚫ In these samples [1], Ti and W were separating,and the contact between W and Ti via Pd was as
only touching.
[1] T. Hayashi, T. Takimoto, et.al., FED, 136 (2018) 545.

However, in order to experiments in tokamaks, it is necessary to modify thesamples from separating structure.
In this work, integrated-type samples have been newly developed.

11Design of integrated samples
Coated Pd(~400nm)

Ti plate (15 mm x 15 mm) has been applied mirror polish.
Magnetron sputtering

Pd has been coated (~400 nm) on Ti plate
Magnetron sputtering

W has been coated (~1 μm) on Pd layerCoated W Ti Plate(~1μm) (0.5mm)
Time [h]Provided by K. Schmid at ASDEX-U

0.5in private communications

10.1
100 200

Thickness [μm]➢ Comparing D permeation timethrough W and a pulse length ofdischarges of ASDEX-U (<0.01h),
W thickness must be less than
100μm at least.
➢ In order to produce such thin W
layer, coated W was selected.
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Design of integrated samples
Coated Pd(~400nm)

Before exposure

Blisters
10μm

Surface morphology by Scanning Electron Microscope (SEM).

➢ Surface observations were performed on produced W-Pd-Ti samples⚫ Blisters (several μm) were observed on the surface.
Coated W Ti Plate(~1μm) (0.5mm)

13Design of integrated samples
Coated Pd(~400nm)

Before exposure

PoreW
Pd

Ti
10μm

Before exposure

2μm

Cross-sectional images after Focused Ion Beam (FIB).

➢ Surface observations were performed on produced W-Pd-Ti samples⚫ Blisters (several μm) were observed on the surface.
Coated W Ti Plate(~1μm) (0.5mm) ➢ Cross-sectional observations were performed on same samples.

⚫ Pores (width of several μm) were observed around the boundary
between Pd and Ti.
⚫ It is not satisfied a good contact between Pd and Ti required tosmoothly permeation due to Pd.

It is necessary to enhance the contact between Pd and Ti.
14Preparation of samples
Coated Pd(~400nm)Ti plates (15 mm x 15 mm) have been applied mirror polish
Magnetron sputtering

Pd has been coated (~400 nm) on Ti plates
Infrared heating

Heat treatment to Pd-Ti samples has been performed
Coated W Ti Plate(~1μm) (0.5mm)

Magnetron sputtering

W has been coated (~1 μm) on Pd layer

Pd-Ti
mixture layer

Heat treatments have been performed to enhance thecontact between these layers by promoting the diffusionof metal particles into each other layer.

diffusion
Pd diffusion

PdTi

Ti

15Preparation of samples
Coated Pd(~400nm)

w/o heat treatment

w/ heat treatment @ 900℃, 1h10μm

10μm

W

Coated W Ti Plate(~1μm) (0.5mm)

Ti
2μm

Temperature[℃]

1000

600
400
2000

123
Time [h]4Heating characteristic

Pd?

Ti

Cross-sectional images after FIB.

8000W

Pd2μm➢ Surface and cross-sectional observations were performed on
also W-Pd-Ti sample with a heat treatment.
⚫ After heat treatment, blisters were not observed on thesurface.
5⚫ Also, pores were not observed between W and Ti after heat16treatment.

Preparation of samples
Coated Pd(~400nm)w/o heat treatment

w/ heat treatment @ 900℃, 1hW

W
Pd
Ti
1μm

Coated W Ti Plate(~1μm) (0.5mm)
Temperature[℃]

0.5μm

The results of Energy dispersive X-ray spectrometry (EDX)on the cross-section of samples.

1000➢ EDX analysis was performed on the cross-sections of bothsamples.
⚫ After a heat treatment, Pd layer was not clear observing byusing EDX.

8006004002000TiPd0123Time [h]4Heating characteristic517

Preparation of samples
w/ heat treatment @ 900℃, 1h
w/o W coating

Coated Pd

w/ heat treatment @ 900℃, 1h10μm

W

Ti Plate(0.5mm)

Ti

The results of X-ray Photoelectron Spectroscopy (XPS)on the surface of the Pd-Ti sample.

Temperature[℃]100080060040020000123Time [h]4Heating characteristic2μm➢ XPS analysis of the surface was performed on the Pd-Ti sample
without W coating after same heat treatment.
⚫ Pd layer was confirmed on the surface of the Pd-Ti sample
after the heat treatment.
5⚫ Pd layer remains on Ti plate after the heat treatment.
18Preparation of samples
It has been clarified that due to heat treatments for 30min at 400℃ or less, pores between Pd
and Ti are removed and the Pd layer is also remained.
w/ heat treatment(400℃ 30min)
w/o W coatingw/ heat treatment(200℃ 30min)
w/o W coatingw/o heat treatment
w/o W coating

20μm20μm50μmw/ heat treatment(600℃ 30min)
w/o W coating

50μm

32Ti

C (x3)
1O (x50)0012345Sputtering time [sec]64C (x3)
Pd
3O (x50)

2Ti
10012345Sputtering time [sec]6Signal intensity [arb. unit]

Pd

Signal intensity [arb. unit]

4Signal intensity [arb. unit]

Signal intensity [arb. unit]

Surface morphologies by SEM on each Pd-Ti sample which varied temperature of heat treatment.
4C (x3)Pd
3O (x50)2Ti1001234

5Sputtering time [sec]64C (x3)

3O (x50)2Ti
1Pd001234

5Sputtering time [sec]Depth profiles of elements in each Pd-Ti sample by Glow discharge optical emission spectrometry (GD-OES).

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Table of Contents◆ Background & Motivation
 Observation of D permeation amount in PFCs

◆ New method to observe D permeation amount Concept of new method
 Design of W-Pd-Ti sample◆ Plasma exposures in the linear plasma device
 Experimental apparatus – the linear plasma device TPDsheet-U Detection of D amount on the sample surface◆ Summary & Future Plans
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Linear Plasma Device TPDsheet-U @ Tokai Univ.
Plasma exposures have been performed to W-Pd-Ti samples using linear plasma device
TPDsheet-U.

Plasma
(D)

YZX

21

Linear Plasma Device TPDsheet-U @ Tokai Univ.
Plasma Source

Experimental region
Sample90 mm

Plasma(D)

YZX

Φ = 8 mmMo

➢ This target is floatingelectrically.
➢ Target potential wasaround -15V during
plasma exposures.

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Experimental Conditions➢ The plasma exposures have performed
to the W-Pd-Ti samples which Pd layer
is thin due to the heat treatment for 1h
at 900℃ by using TPDsheet-U.
w/ heat treatment @ 900℃, 1h

Plasma Conditions
Sample No.

Ion Flux

Gi[m-2s-1]

Electron Density

ne[m-3]#29~ 1.8x1022~ 7.7x1017

Electron Temp.

~ 4.8

Te [eV]
10μm

Exposure Timet
Ion FluenceW

Gi ∙ t [m-2]

PdTi
2μm

#303h

4 min

~ 2.0x1026~ 4.5x1024

High fluence

Low fluence
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Results of plasma exposures
Back sidePlasma facing side1040C8H25Counts6W

Ti

Plasma-facing side

DERDA, 4He, 2.8 MeV

H

No.29, flue 2E26
No.30, flue 4E24

20215D1050-2

CERDA, 4He, 2.8 MeV

No.29, flue 2E26
No.30, flue 4E24

4Back side

30

Counts

Pd

00500

1000
1500
Channel number

2000-505001000
1500
Channel number

2000

Spectrum of Elastic Recoil Detection Analysis (ERDA) .

➢ Measurements of D amounts by ERDA were performed on sample
surfaces of plasma-facing side and back side.
⚫ D was detected on both sides of samples.
⚫ At the back side, D was detected in only high fluence condition (#29).

Photo of the experiment

It has been success to detect D on Ti surface (back side) ofW-Pd-Ti sample.

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Table of Contents◆ Background & Motivation
 Observation of D permeation amount in PFCs

◆ New method to observe D permeation amount Concept of new method
 Design of W-Pd-Ti sample◆ Plasma exposures in the linear plasma device
 Experimental apparatus – the linear plasma device TPDsheet-U Detection of D amount on the sample surface◆ Summary & Future Plans
25

Summary & Future Plans
Summary✓ There is no precedent for direct evaluation of hydrogen permeation in PFCs under high flux plasma
exposures in fusion devices.
⚫ We have newly developed the integrated W-Pd-Ti sample as a new method to quantitatively evaluate theamount of hydrogen permeation during high flux plasma exposures in fusion devices.
✓ In first sample preparation, pores which it is considered to impede D permeation to Ti were observed aroundthe boundary between Pd and Ti layers.
⚫ It has been clarified that due to heat treatments for 30min at 400℃ or less, pores between Pd and Ti areremoved and the Pd layer is also remained.
✓ Plasma exposures have been performed to W-Pd-Ti samples using TPDsheet-U.
⚫ It has been success to detect permeated D at Ti surface (back side of samples) by ERDA after plasma
exposure with enough ion fluence (ex. ~2.0E26 m-2).

Future Plans
 Investigation of fluence dependence and material, which is W-Pd-Ti samples, temperature dependence ofplasma driven permeation in TPDsheet-U.
 Plasma exposures in fusion devices such as ASDEX-U.

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Thank you for your attention
Acknowledgement
This work is performed with the support and under the auspices of the NIFS
Collaboration Research program (NIFS17KEMF109).
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