Report on SEWG mixed materials EU PWI TF meeting Madrid 2007 V. Philipps on behalf of SEWG members Mixed material formation is a among the critical ITER

Report on SEWG mixed materials

EU PWI TF meeting Madrid 2007

V. Philipps on behalf of SEWG members

Mixed material formation is a among the critical ITER PWI issues

PFC erosion and lifetime

consequences for T retention

Outline

• Overview summary of SEWG meeting July 2007 at JET

• SEWG view on importance of material mixing in ITER

• Future activities

IntroductionSEWG mixed materials EU PWI TF

V. Philipps, EU PWI TF meting, Oct 2007, Madrid

EU PWI Task Force

V. Philipps, SEWG mixed materials, 9.07.2007, JET

Beryllium

Tungsten

Carbon

ITER material choice

Main important systems

1. Binary systems

Be impact on W

Be impact on C

C impact on W

W impact on C

2. Ternary systems

Be/C/O layers

W/C/O (Be) layers

Importance for

Erosion

Fuel retention

SEWG mixed materials EU PWI TF


Binary systems:Be on C and W (Pisces , IPP lab experiments) Deposition studies of mixed layer formation (Romania) W-C mixed layer formation (TEXTOR)

Ternary systemsBe-W-C system (IPP lab experiments) Mixed Be/C/O layer formation in (JET)

D retention in mixed materialsD retention in pure and O-covered Be (IPP)Co-deposition of D with Be (Pisces) EFDA RETMIX task (IPP) Modelling of mixed layer formation Parameter studies of Be-W interaction (IPP) Ero- Tridyn of mixed layer formation (FZJ) DIVIMP of Be-W interaction in ITER (IPP) Mol-Dyn modelling of mixed layer formation (Tekes)

SEWG meeting July 2007

Presentations

PISCES

• simulate interaction of Be (which is eroded from main chamber in ITER and transported to the divertor) with the W

baffles and C dump plates • co-deposition of re-eroded material with fuel using witness

plates (e.g. the situation at the ITER dome)

Cooperation EU - PISCESLong term visits Modelling

K. Schmid ERO (A. Kirschner, D. Borodin)R. Pugno K. Schmid

next: A. Kreter

+ hard ware , post mortem surface analysis



EU-Pisces cooperation

WBe

Be-flux: fBe * Г D

D- flux : ГD

Re-eroded Be flux: ГD *YD

(Plasma temperature)

Be

D

Evaporated Be flux: Г Be evap

(Surface temperature)

Be diffusion in W (Surface temperature)



Determining parameters

Be flux ratio, Be re-erosion, Be evaporation, Be diffusion in W

Be on W

Be-W allows form effectively in the temperature range 850-1300K. (e.g. a 0.3 mm Be12W layer forms at 1070K, 10eV, 0.3% Be in 1h exposure (≈1026D/m2)

At lower temperatures (< ≈ 900K) Be diffusion is to low for (thicker) Be-W alloy formation

At higher temperatures (> ≈ 1200K) Be sublimation competes with Be diffusion, limiting the Be-W allow formation

If Be re-erosion exceed Be deposition flux, only Be-W islands form on the W surface



Be on W: summary Pisces

R. Doerner et al



Be on W: summary Pisces

R. Doerner et al



Be on C: IPP lab experiments

substrate

Evaporation (5 1016/cm2)

crucible

Be, C

Be , C

XPS

Annealing

Principle of experiments

C. Linsmeier et al



first additional Be2C after 773 K

indications for island growth

5 x1016 Be deposited on C, Be 1s intensity

metalliccarbidic

Transition to Be2C between 670 and 770K

Be on C: IPP lab experiments

C. Linsmeier et al

69,6%

2,3%

36%

2,5%

41,6%

3,0%

27,3%

3,5%

open gap shadowed gapPlasma-

Erosion zone

Deposition zone

Tungsten exposed under erosion conditions, W – C intermixing in gaps,

Strong W-C mixing at plasma closest edge, W content decrease fast with distance

No chemical state analysis so far



TEXTOR gap deposition experiments

A. Litnovsky et al

W-fraction

Mixture of Be, C, W

970 K

CBeW

216cm102.1 216cm109.2



C. Linsmeier, F. Kost et al

W2C

amount

Be2C amount

• Full Be2C formation: 560 K (increasing with depth)

• Formation of W2C (decreasing with depth)

• Small amount of WC at T > 1170 K• No Be2C at T > 1170 K

Lab data: Ternary systems



mitigation of chemical erosion of C by Be- deposition

Time (s)0 500 1000 1500 2000

0.1

1

0.18 % Be0.41 % Be

0.13 % Be

1.10 % Be

0.03 % Be

No

rm.

CD

Ban

d s

tren

gth

[a.

u.]

Modelling with flux models and ERO Tridyn

Optimise predictions for ITER divertor C- erosion

Modelling

A. Kirschner, D. Borodin



Best agreement with TriDyn surface model with the assumption that all Be bound in carbide

However complete suppression of chemical erosion in experiments at lower Be concentrations (less than 1%) than needed in ERO (several percent).

Characteristic time of erosion mitigation in modelling smaller than in experiment.

Dedicated surface morphology to be included ?

A. Kirschner, D. Borodin

Ero modelling



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

Global Be erosion deposition modeled based on B2 Eirene input, Divimp transport modeling and a flux balance surface model , includes: eErosion from main wall, Be-transport to divertor, Be re-erosion and transport in the divertor

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)

0.1000

0.3000

0.5000

0.7000

0.90001.000

Be surface concentration in EQ

Peak layer growth 0.03nm/sDome Be-deposition by re-erosion

Global ITER modelling

K.Schmid et al

Flux fractions range from 1% percent levels in the inner divertor to 0.01 % levels in the out divertor

Thick Be layers are expected in the inner divertor and dome

Be flux in outer divertor may be to low to mitigate C chemical erosion

Temperature in layer deposition zones not high enough for alloy formation under steady state conditions ( no temperature excursions)

Based on current experimental thermodynamic data for the Be/W system temperature excursions can lead to formation of thick Be/W layers



K.Schmid et al

Global ITER modelling



Mixing and T codeposition

A very detailed and solid investigation of retention of energetic D in pure and O covered Be has been done

• Maximum local concentration D/Be=0.35

• Saturation at about 2 1017 D cm-2

• Nearly constant retention up to 530 K

• No significant influence of BeO coverage

• Maximum retention in ITER for 1 keV / 0° incidence < 7g

Matthias Reinelt & Christian Linsmeier



0.001

0.01

0.1

1

0 100 200 300 400 500 600 700 800

D/CD/BeOD/BeD/BeD/BeD/WD/(W+C)D/(Be+C)

Temperature (C)

T retention by codeposition

R. Doerner et al Still a large scatter in T retention fraction

Latest data indicate that the impurity fraction is not determining the retention in B codeposits

The codeposition conditions seems to determine the layer structure of the codeposits

layers deposited at higher ion energies tend to retain more D (recommended value: D/Be = 8%) than those with lower ion energies (recommended value 1%)



Future

Influence of transient temperature excursions on Be- W and Be-C interaction (Pisces, Lab)

Address open issues (lab studies) on reaction kinetics of Be-W and Be-C (e.g. Be / W interdiffusion, Be sublimation from Be / W alloys, etc....

Furthers studies of ternary systems (Be-W-C)

Hydrogen retention in codeposited material combinations: influence of layer structure , surface morphology etc. ( e.g Retmix task)

Implement latest Be flux results in ITER Ero modelling of erosion/deposition and T retention

MD modelling

Documents

Report on SEWG mixed materials EU PWI TF meeting Madrid 2007 V. Philipps on behalf of SEWG members Mixed material formation is a among the critical ITER