v.philipps, sewg mixed materials, eu pwi meeting frascati, oct 2008 eu task force plasma wall...

V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008

EU Task Force Plasma Wall Interaction

SEWG material mixing, report on 2008 activities

V. Philipps on behalf of all SEWG members


Beryllium

Tungsten

Carbon

1. Binary systems

Be impact on W (compound formation, enhanced erosion of W ↓)

C impact on W (embrittlement of W ↓)

Be impact on C (reduction of C chemical erosion ↑)

W impact on C

2. Ternary systems

Be/ C / O

W/ C/ O (Be)

new compounds?, influence of oxygen

role of seeded impurities

3. Modelling, ITER extrapolations


Year Associate(s) Baseline Support (ppy)

Priority Support (ppy)

remarks

2008 PWI-08-TA-08/FZJ/PS/00Task Coordinator : V. Philipps

FZJ 3/12

PWI-08-TA-08/CEA/BS/01Molecular dynamic simulations of mixed materials

CEA 6/12

PWI-08-TA-08/FZJ/BS/01ERO-modelling of PISCES-B results. Coupling of ERO with SDTrimSP

FZJ 5/12 Report (SEWG meeting)

PWI-08-TA-08/FZJ/PS/01ERO-modelling of mixed materials (ITER application)


PWI-08-TA-08/FZJ/BS/02Analysis of mixed W-C layer formation in gaps of ITER like castellated W targets


PWI-08-TA-08/IPP/BS/01Binary and ternary systems (Be, C, O, W), kinetic simulation of material mixing

IPP 36/12 Report (SEWG meetin)

PWI-08-TA-08/IPP/PS/01Joint investigation of fuel retention in Be-C/W layers

6/12

PWI-08-TA-08/IPP/BS/02Dual beam experiment D+C on W

IPP 10/12 Report (SEWG meeting)

PWI-08-TA-08/IPPLM/BS/01Post mortem analysis of mixed layers formation: TEM, FIB, SEM, EPMA, XRD, AES etc

IPPLM 4.5/12 Report

Workprogramme 2008


PWI-08-TA-08/IPPLM/BS/01Post mortem analysis of mixed layers formation: TEM, FIB, SEM, EPMA, XRD, AES etc

IPPLM 4.5/12

PWI-08-TA-08/IST/BS/01Characterization of samples

IST/ISN 2/12 No samples delivered

PWI-08-TA-08/MEDC/BS/01Preparation of mixed Be-C&W layers and analysis of retention

MEdC 12/12 Report (SEWG meeting)

PWI-08-TA-08/SCK/BS/01Refurbishment of the plasmatron VISION I

SCK-CEN 3/12 Report (SEWG meeting)

PWI-08-TA-08/TEKES/BS/01MD modelling of mixed layers (W, Be),

TEKES 18/12 Report (SEWG meeting)

PWI-08-TA-08/VR/BS/01Post mortem analysis mixed layer formation

VR 5/12 Report (SEWG meeting)

PWI-08-TA-08/VR/PS/01Post mortem analysis mixed layer formation on PFC in TEXTOR and other EU devices

VR 2.4/12 Report (SEWG meeting)

Total 104.5/12 13.4/12


Vessel Walls 1. High flux case 1x1024/s (Tokamak experience)2. Low flux case 1x 1023/s ( B2-Eirene estimate)

2% Be erosioncase 1:50% dep. in main chamber

37.5% dep. in inner divertor15.5% dep. in outer divertor

case 2:75% dep. in inner divertor25% dep. in outer divertor

ITPA DIV SOL: New empirical scalings combined with modelling

(EU contribution: J. Roth (coordinator), A. Kallenbach, A. Kirschner, O. Ogorodnikova, V. Philipps, K. Schmid, G. Wright )

Impurity fluxes and distribution in ITER

Divertor: Fluxes from B2_EIRENE (equilibrium 1084): total divertor flux 3x1024/sImpurity flux distribution from Divimp ( K. Schmid)Divertor erosion deposition: ERO code with Divimp distribution, matched to the total impurity fluxes


4.0 4.5 5.0 5.5 6.0 6.5

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

Z(m

)

R(m)

1.000E-8

1.000E-7

1.000E-6

1.000E-5

1.000E-4

1.000E-3

0.01000

0.1000

Be-Flux fraction in EQ

Further work underway, e.g on Be distribution

K. Schmid, EU PWI TF meeting 2007

SEWG mixed material group should assume a reasonable wide range of impurity fluxes and distributions


Recent results from Pisces (EU-Pisces cooperation )


EU-Pisces cooperation1. Extended retention scalings of D in Be, W, C

literature survey of retention data of D in C, W, Be combined with PISCES data

2. Influence of Argon on Be-C interaction

3. Development of W-nanostructures

EU-PISCES cooperation

Sample analysis (IPP )Long term visitor (A. Kreter)Ero modelling of Be/C interaction ( FZJ)


For Beryllium:

For Tungsten

For Carbon

D/C = 0.0204 E –0.43 (D/C)0 exp(2268/Tc)

293 < Tc < 473 K

473 < Tc < 973 K 15 < E < 100 eVD/C < ? large

293 < Tc < 600 K 15 < E < 62 eVD/Be < 2000

293 < Tc < 600 K 60 < E < 280 eVD/W < 500

Models overlap: 293 - 600K~60 eV ~10s - 1000s flux ratios

D/Be = (5.82 x 10-5)En1.17 0.2 (

D/Be)-0.21 0.1 exp(2273 311/Tc)

D/W = (5.13 x 10-8)* En1.85 0.4 * (

D/W)0.4 0.1 * exp(736 228/Tc)

D/C = 0.0204 E –0.43 (D/C)0 exp(2268/473)

Topic: fuel retention in mixed layers:

retention scalings of D in Be, W, C

R. Dörner, SEWG meeting, 9-10.10. 2008


Roth PPCF 2008

Retention level Scaling (523K, 20eV, D/X =100)

Scaling (523K, 60eV, D/X =100)

0.6 (D+T)/C 0.4 0.3

0.03 (D+T)/Be 0.05 0.2

0.002 (D+T)/W 0.0003 0.003

x

x

x

(D+T)/W~ 0.002

(D+T)/Be ~ 0.03

(D+T)/C~ 0.6

- Codep with W is small- flux arrival factor is not a large effect- Particle energy arriving at the codepositing layer plays a big role

1. Extended retention scalings of D in Be, W, C



• Codeposits formed at higher temperature retain less deuterium/tritium

• D accumulation from W codeposition is negligible

• D content of Be and C codepoists can be comparable– D content can be significantly less in Be codeposits

formed at lower incident particle energy locations (i.e. divertor and dome)



Topic: chemical erosion of Be-C mixed system

500

1000

1500

2000

2500

3000

3500

4000

No Be injection0.2% Be ion concentration

Wavelength (nm)

CD band

D gamma Be I

459445431 452438

10-4

10-3

10-2

10-1

100

101

0 100 200 300 400 500 600In

tens

ity [a

.u.]

Time [s]

ID

IBeI/ID

ICD/ID(near)-ICD/ID(far)

20060322

Be/C = 86±1 sec


Present data: a small beryllium impurity concentration in the plasma drastically suppresses carbon erosion with a characteristic decay time


CD band decay time similar with and without argon


Addition of Ar to the plasma does not affect the mitigation of carbon chemical erosion by beryllium


Topic: surface modifications of W due to high fluence mixed-species (D, He, Be) plasma interactions with W

layers of Be suppresses blister formation (300-700 K )

• At 550 K a blistered surface is prevalent after exposure to D2 plasma.

• A thin layer of Be as little as a few 10’s of nm suppress blister formation and D retention.

R. Dörner , SEWG meeting, 9-10.10. 2008


Mixing He with D-plasma suppresses also blisters on W surface

and reduces D-retention in W.

Pure D2 plasma (SRWM-3b)

D-fluence ~ 5e25 m-2, D ~ 1.0e22 m-2s-1, Ts ~ 573 K, Ei ~ 60 eV

D2-He mixture plasma (SRWM-4b)

D-fluence ~ 5e25 m-2, D ~ 0.9e22 m-2s-1, Ts ~ 573 K, Ei ~ 50 eV, nHe+/ne ~ 20 %


Similar new results by Alimov et al


Topic: development of surface nanostructures

Nano-morphology develops only above 900 K.

Ts = 1120 K, He+= 4–6×1022 m–2s–1, Eion ~ 60 eV

Fluence



• Observed t1/2 proportionality.

• The thickness of the nano-structured layer, d, agrees well with

<d>=(2Kt)1/2,with,K1120 K = 6.6 0.4 10–16 m2s–1

K1320 K = 2.0 0.5 10–15 m2s–1

• Overall process is consistent with an activation energy of ~0.7 eV.

t1/2 (s1/2)

0 50 100 150

Laye

r th

ickn

ess

, d (

m)

05

Ts=1120 K

Ts=1320 K

Nanostructures are observed on various W materials, also doped W materials


In D2−He plasmas : nano-morphology persists, growth rate depends on He+ flux.

Simultaneous Be deposition but with no development of thick Be layer ( Be re-erosion dominates deposition, nano-morphology development is enhanced

A thick Be or C layer inhibits nano-morphology..

Importance for various PWI processes not fully clear but

Liner and dome (T below 900 K).– Minimal Be−W alloy or He induced nano-morphology– Be and/or He may alleviate also W blistering.

at W strike-points (T above 1000 K).

– Be−W alloy and/or He induced nano- morphology can develop !!


Structure-dependent deuterium retention in beryllium:

comparison between Be (11-20) and Be (poly)C.Linsmeier et al , IPP

PWI-08-TA-08/IPP/BS/01

D ion implantation (1 keV) in single and polycrystalline Be ► thermal desorption spectroscopy

Structural modifications

Structural modifications

Local saturation of available

binding sites

Local saturation of available

binding sites

Trapping in ion induced defects

Trapping in ion induced defects

400 600 800 1000

Fluence

[1015cm-2]144

124

122

92

65

47

Desorp

tion r

ate

[a.u

.]

Temperature [K]

C. Linsmeier, SEWG meeting, 9-10.10. 2008

Topic: T retention in bulk Be


[ES = -0.10 eV] Atomic D E0≡ 0

[ΔEAd = 0.87 eV]

Molecular D2

[EBE (1/2 D2) = -2.278 eV]

Surface

Mobile state

[ΔED = 0.29 eV]

E (D-Atom)

Activation energies obtained from modeling of TPD spectra

Tem

per

atur

e [K

]

Desorption rate [a.u.]

ΔE = 1.25 eV 1.33 eV

ΔE = 1.9 eV 2.1 eV

(simple model)

Ion-induced defects

Supersaturatedstates



Deuterium retention in beryllium

Binding states & retention mechanisms described in a simple model

Surface recombination not rate-limiting for thermal recycling Vacancy clusters determine highest release temperature

Hydrogen retention in ITER: negligible contribution of "pure" Be wall (< 7 g T by implantation)



Tokamak observations


Formation of mixed W/C layers in the gaps of castellated structures, A. Litnovsky

69,6%

2,3%

36%

2,5%

• Strong W intermixing near the top of the gap (up to 70 at. % of W)

• Strong W-decay with depth ( much shorter as C)

• Influence on possible cleaning ?

C deposition in gaps while surface is erosion dominated

A. Litnovsky , SEWG meeting, 9-10.10. 2008PWI-08-TA-08/FZJ/BS/02

Poloidal gaps


Low W fraction detected in the deposits: Wfr.max<10 at.%

Large differences of W intermixing in toroidal and poloidal gaps

W mixing in toroidal gaps

D=5.51C= 20.4D/C=2.7

D=0.98C=13.4

D/C=0.73

D=3.29 C=25.3D/C=1.3

Wfr.max 4%

D=10.09C=19.9D/C=5.5

Wfr.max 4%

D=9.68C=44.8

D/C=0.38Wfr.max 10%

D=1.07C=28.2

D/C=2.16Wfr.max 10%

D=3.26 C=39.8

D/C=0.82Wfr.max 5%

D= 15.8C=28.2D/C=5.6

Wfr.max 5%

Bt

Left of field line direction

Right of field line direction

Geometry and plasma impact effect

Under analysis


Inner divertor: Tiles 1 and 3 analysed with SIMS and RBS so far

heavy deposition

•SIMS depth profiles from inner divertor wall tile 1 and 3

•Deposit: Be/C high (varies as a function of depth)

•Low vessel temperature (200oC)layer D (at

%)Be (at%)

12C

(at%)

13C (at%)

O (at%)

1 3 25 57 3 12

2 3 53 25 19

3 3 22 59 15

4 1 46 44 8

5 6 19 69 6

New data from 2005-2007, MkIIHD JET campaign

J. Likonen , SEWG meeting, 9-10.10. 2008

High Be content in deposited layers on plasma wetted areas

PWI-08-TA-08/VR/BS/01

Mixed Be/C layer formation in JET


JG

03

.67

6-1

c

layer D (at%)

Be (at%)

12C

(at%)

13C (at%)

O (at%)

1 18 0.5 57 9 15

2 16 3 68 13

3 15 3 68 13

Previous results: Composition of deposits in the PFR (2001-2004, MkIISRP)

Low Be content in (C) - layers on remote areas

J. Likonen , SEWG meeting, 9-10.10. 2008


JET Be toroidal belt limiter

• Operation: 1989 – 1992

• 56 000 s of plasma

• 2000 castellated blocks.

Castellated bulk Beryllium JET limiters VPS-Tungsten Coated Limiters (TEXTOR) ( M. Rubel)

Small amount of deuterium retained in solid Be .

Co-deposition of deuterium with carbon.

More deuterium in areas which were molten.

Bridging of gaps by molten metal.

M. Rubel , SEWG meeting, 9-10.10. 2008

PWI-08-TA-08/VR/PS/01

Post mortem analysis of


• No or very little deuterium detected in bulk beryllium . Small amount of co-deposited deuterium with carbon on all surfaces of Be belt limiters.

• CD (castellation) / CD (top surface) ~ 0.4

• Short decay length l ~ 1.5 – 2.0 mm for deuterium and carbon in co-deposits.

• No difference in fuel content and carbon co-deposition between toroidal

• castellated grooves and poloidal gaps between tiles.

• Deuterium is found in the surface layer of BeO.

• Deuterium in areas which were molten.

• Bridging of gaps by molten metal.



X

• W carbides and borides found

• Deuterium only with carbon

• Amount of D in W: < 5x1014cm-2

Side wall analysis Main phases: Graphite and W carbide: WC• Traces: Tungsten and Tungsten

carbide: W2C

• The same phases found in all analysed

points on both sides of limiter block.

Limiter_A2a - File: Limiter_A_2a.raw - Type: 2Th/Th locked - Start: 20.000 ° - End: 129.999 ° - Step: 0.019 ° - Step time: 486.5 s - Temp.: 25 °C (Room) - Time Started: 23 s - 2-Theta: 20.000 ° - The

Sqr

t (C

ount

s)

10

100

1000

2000

3000

2-Theta - Scale

34 40 50

W2

CW2CW2C W

C

C

C

WC WC

35

45 40

50 55 101

103

102

3x103

2 scale

Inte

ns

ity

[sq

rt

sca

le]

TEXTOR VPS poloidal W limiters

Side wall



Post mortem examinations of divertor strikepoint tiles of ASDEX-U (E. Fortuna et al)

PWI-08-TA-08/IPPLM/BS/01

Material

9 samples from 2 divertor strikepoint tiles:

Tile 1 from the outer strikepoint region, coated with a 200 µm W VPS layer

Tile 2 from the inner strikepoint region, coated with ~4 µm W

• Tiles installed from 4 o 10/07 (All PFCs tungsten coated)• No boronisation performed


AES examinations (Microlab 350)Tile 1 (outer divertor)

SEM image of the tile topography and AES spectrum from position 1

Results of point analyses

Position C. at.% W at.% O at.%

P1 32 54 10

P3 39 49 12

P4 35 60 5

1

3

4

W-C intermixing observed


Surface morphologyTile 2 ( inner divertor)

deposit

disclosed tungsten coating

Compact, glassy-like layer of deposit

Stratified character of deposit layer

50 m 25 m

5 m 10 m


Laboratory experiments


Topic: W - C interaction

chemical and physical sputtering processes under simultaneous C-D irradiation of W (H. T. Lee, K. Krieger et al)

H. T. Lee, K. Krieger SEWG meeting, 9-10.10. 2008PWI-08-TA-08/IPP/BS/02


0.0 0.1 0.2 0.3 0.4 0.5 0.60.0

0.2

0.4

0.6

EXP. TRIDYN25% : 16% : 13% : 7% :

Imp

lan

ted

C (1

022 m

-2)

W Sputtered (1022 m-2)

Continuous W Erosion

C layer growth

6keV C + 3keV D W

Transition point : 9%<fc<10%

Detailed study of C implantation, re-erosion and layer growth depending on exposure parameters & temperature

Comparison with Tridyn modelling

C selfsputtering on W enhanced (deviations at 600C )

Importance of C chemical erosion on W

Decreases from RT towards 500C

H. T. Lee, K. Krieger SEWG meeting, 9-10.10. 2008



Topic: thermal behaviour of multispecies mixed layers

Detailed lab study of the thermal stbility of the ternary Be –C –W system ( C. Linsmeier et al )

F. Kost, C. Linsmeier SEWG meeting, 9-10.10. 2008



Be

Be

C

C

W

W

Be2W + Desorption

Be12W (Be-Diffusion)

W2C and WC(C-Diffusion)

Su

bst

rate

Layer

CurrentExperiments

Be2C (Be-Diffusion)


C

Be

W

Be/C/W

C

Be

W

0.88 nm

1.15 nm

2.7 nm

1.6 nm

1

2

excess of C

excess of Be

Heat treatment: RT, 570 K – 1270 K



elem.C

excess of C excess of Be

XPS data



Carbide formation at RT at both interfaces Be2C phase dominating

formation at 770 K dissociation at 1070 K

Be desorbs / dissolves in WC forms tungsten carbides

Remaining Be diffuses to the substrate Be2W formation at T > 670 K Be2W loss at 1070 K

W2C formation at T > 1070 K WC formation at T > 1170 K



Lab study of the ternary system Be-O-W

(thin Be-Layers on different Tungsten Oxides ( WO2 and WO3-x)

► heating from 300 °C – 1000 °C in steps of 100 °C for 30 min

C. Linsmeier SEWG meeting, 9-10.10. 2008


• 673 K, 773 K, 873 K: Decay of BeWO3

• 973 K: Formation of BeWO

• 1073 K, 1173 K, 1273 K: Decay of BeWO4

Be on WO3: Main Reactions

Be on WO2

In contrast to WO3 , tungsten dioxide does not react much with beryllium

WO2 first shows a real reaction at its dissociation temperature of 1273 K

Explained by different structure of WO3 ( more open porosity) compared with WO2

C. Linsmeier SEWG meeting, 9-10.10. 2008


Topic : modelling of mixed layer formation

Molecular dynamics modelling of mixed layer formation K. Nordlund et al

Potential development for the Be-C-W-H system

Structure change and erosion of WC during high-dose D bombardment

Structure change and erosion in BeC

PWI-08-TA-08/TEKES/BS/01 K. Nordlund, SEWG meeting, 9-10.10. 2008

MD simulations : optimise potentials for special systems

Detailed study of the WC system has been done


ERO Modelling of Erosion and Deposition of Mixed Materials: PISCES-B & ITER ( A. Kirschner , D. Borodin)

-10 0 10 20 300

2

4

6

8

10

12

14

16

x 1016

Ch

em

ica

l ero

sio

n [

CH 4/s

]

Time from injection start [s]

1.0e+018 Be/s3.0e+018 Be/s1.0e+019 Be/s3.0e+019 Be/s

Modelling of the chemical erosion of C during Be deposition in Pisces

-10 0 10 20 300

2

4

6

8

10

12

14

16

x 1016

Ch

em

ica

l ero

sio

n [

CH 4/s

]

Time from injection start [s]

1.0e+018 Be/s3.0e+018 Be/s1.0e+019 Be/s3.0e+019 Be/s

no Be-C carbide formation with Be-C carbide formation

A. Kirschner, SEWG meeting, 9-10.10. 2008


1. Deviations between simulated and experimental axial Be profiles (Be density & transport) clarified by implementaion of new tools in ERO Pisces simulation.

2. Modelling indicates strongly spontaneous Be-C formation with complete suppression of C chemical erosion of carbidised C.

3. Still differences between modelling and experiment

1. different time scales (faster decay in simulation)

2. complete C erosion mitigation in modellling only in case of high concentrations of Be in plasma


Importance of additional processes

surface roughness effects

inhibition of chemical erosion of a large number of C atoms


Status of ERO Modelling for ITER: implementation of new T/ Be,C retention scaling for mixed layers

-0.2 0.0 0.2 0.4 0.61E-4

1E-3

0.01

0.1

1

(T+D)/Be (T+D)/C

distance along inner target (m)

(T+

D)/

Be

, (T

+D

)/C

0

1x1015

2x1015

3x1015

4x1015

5x1015

Be deposition C deposition (*10)

Be

, C d

ep

so

ition

(pa

rticle

s/m

m2s

)Example Inner target: resulting (T+D)/Be and (T+D)/C



on target remote

beryllium carbon beryllium carbon

(D+T)/Be

=0.1

(D+T)/Be

~fit

(D+T)/C

=0.1

(D+T)/C

~fit

(D+T)/Be

=0.1

(D+T)/C

=1.0

outer 0.9 0.17 0.2 0.27 0.02 0.8

inner 6.0 1.3 0.02 0.1 0.1 0.1

Revised estimated T retention rates



Gas, plasma, secondary ionsand neutrals analyser

CW

CW

Cooling Water (CW)Isolation

(I)

I

Permanentmagnets(PM)

PM

Cathode

Anode

Target

Ultra High Vacuum (UHV 1)

UHV 2

Thermo-couples(TC)

Inletgas

Cathode

UHV 3 Gas, plasma, secondary ionsand neutrals analyser

CW

CW

Cooling Water (CW)Isolation

(I)

I

Permanentmagnets(PM)

PM

Cathode

Anode

Target

Ultra High Vacuum (UHV 1)

UHV 2

Thermo-couples(TC)

Inletgas

Cathode

UHV 3

Status of the plasmatronVISION I (I. Uytdenhouwen

PWI-08-TA-08/SCK/BS/01

I. Uytdenhouwen SEWG meeting, 9-10.10. 2008

• re-establishment of the vacuum systems June 2008explanation of the working system

Design of a new frame. Plasmatron: removed in parts from the gloveboxes and will be

rebuilt outside. Sensors, valves will be checked and replaced in case of

damage. Vacuum chambers need to be investigated on their status

(electropolished surface, leak tightness, …). Connections (vacuum tubes, cooling, …) will be subject to a

maintenance. Electric circuit diagram and layout control cabinet are ready Assembly new control cabinet has started Development control software has started …

• plasma generation December 2008

For this goal more software control of the valves and pumps is needed

Filaments and targets were purchased and replaced Minor instrumentation should be present and will be set up

soon

Good progress has been made


Summary

Successful workprogramme executed

Scaling of T retention in deposits

Development of W surface structures

He &Be prevents blistering

Diffusion dominated nanostructure growth

Behaviour of H in solid Be

Dynamics of W-C system ( selfsputtering, chemical erosion)

Be-C chemical erosion behaviour versus modelling

ITER modelling on material mixing and T retention

And …..

To be done:

Including seeded impurities (inert gases, N, ..) in mixing

More close coupling of MD modelling to observations (?)


Most critical issue (from present view )

Development of W surface structures and/or Be-W compounds in the T range 800-1300K

v.philipps, sewg mixed materials, eu pwi meeting frascati, oct 2008 eu task force plasma wall...

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