Report on SEWG ITER like Material Mix V. Philipps on behalf of SEWG working group* Decided during EU -TF meeting Cadarache, 2005 Work programme defined

Report on SEWG ITER like Material Mix V. Philipps on behalf of SEWG working group*

• Decided during EU -TF meeting Cadarache, 2005

• Work programme defined in a first SEWG meeting (June 2006 , IPP Garching )

* presently: P. Coad, M. Rubel, J. Likonen, K. Nordlund, A. Kreter, A. Litnovsky, A. Kirschner, D. Borodin, S. Droste, C.Linsmeier, K. Krieger, M. Mayer, U. von Toussaint, K. Schmid, J. Roth, C. Lungu, R. Doerner, M. Baldwin, E. Fortuna, I. Uydenthoven

EU Plasma-Wall Interactions Task Force

V.Philipps, EU TF Meeting, Slovenia, 13-15 Nov 2006

…The aim of the SEWG is to improve our knowledge and initiate new experiments and modelling for mixed materials formed on deposition dominated areas or in the narrow surface layer on erosion areas for the ITER like material mixfor the ITER like material mix.

The focus of the work is to clarify in more detail important physical properties of mixed layers which are of relevant for PWI processes in fusion devices:

• Chemical composition• Thermo-mechanical properties • Hydrogen retention properties• Erosion behaviour, including alloy formation and thermal

decomposition

The work of the SEWG is not to analyse the underlying processes of material erosion and its migration…. This is the main focus of other working groups…..



Motivation

Systems• Be on W & C • W on C • C on W• W & C on Be

Tertiary systems (mixed Be, C, W ,O)

Oxygen important additional impurity



The most important topics



Be on C (with O)

•Ion beam implantation , C films on Be (IPP Garching)

•JET Be –C experiences : Be limiters, Be-C mixed layer deposition in inner divertor (UKAEA, Tekes, VR, FZJ, SEK )

•Pisces Be seeded plasma interaction with C (Pisces, IPP)

•Modelling (IPP, FZJ)



Be on C (with O)

1. Ion beam data C+ , CO+ → Be

P. Goldstrass, C. Linsmeier : formation of mixed layers and compounds on beryllium due

to C+ and CO+ bombardment, J. Nuc. Mat. 290

P. Goldstrass, W. Eckstein, Ch. Linsmeier: Erosion of beryllium and deposition of carbon and oxygen due to bombardment with C+ and CO+ ions, J. Nuc. Mat. 266

2. Thermal annealing: a-C:H on Be

J. Roth , W.R. Wampler, W. Jacob: release of deuterium from carbon-deuterium films on beryllium during carbide formation and oxidation, J. Nuc. Mat. 250

Annealing of a-C:H on Be J. Roth , W.R. Wampler, W. Jacob, J. Nuc. Mat. 250

at ~ 490C, Be - C mixing starts

a-C:H deposited on Be

At 560C, Be2C fully formed, D is thermally released



heatingC

D

C

D

C

Be

Be

Be

no significant carbon dissolution in bulkstable surface carbide at elevated temp.

C on Be (with O)

Oxidation is determined by diffusion of Be through BeO, (confirmed by 16,18O isotope experiments )



O on Be

Oxide layer before

Oxide layer after

No significant

reaction at 375 C

oxidation starts not before 400C

Be

BeO

O2

BeO

Oxidation of Be in O2 ( 660mbar )



Be – O interaction

Small temperature window exists at which C layers are oxidised while the Be substrate is not

300 C < T < 375 C

With C and O simultaneously impacting on Be, BeO is more stable and favorised than Be2C

( C. Linsmeier)

Atomic oxygen:

interaction with binary metal-C systems

and ternary metal—C—O systems

Be—W system:

reaction kinetics of alloy formation

reactivities with C, O

Hydrogen inventory:

clean and oxide/carbide covered beryllium

tungsten systems (W, Be—W)

Be—W ternary (C, O) systems

Structural investigations:

STM studies of carbon films on metals (Ni, Be, W)

modifications due to deuterium ions

PISCES collaboration:

EFDA task TW5-TPP-CARWBER

Current and planned IPP Garching lab activities on fundamental surface processes:

Ch. Linsmeier et al.

Codeposition of Be with C and O on collector probe after first JET_ Be evaporation (1989)

LCFS

SOL collector probe

30 40 70 (mm)

More BeO

More Be2C

P. Coad et al , Journ. Nucl. Mat. 176 & 177 (1990) 145



Be–C- O: previous JET experiences

Be2C formed close to LCFS and BeO deeper in SOL

Parameter: impinging flux composition, temperature (?)

0


V.Philipps, ITPA Toronto 2006

Material transport ways in JET

1: C rich layers built up in shots with smaller Elms, only some C is transported further

2. In large ELM shots, C (not Be) is released and transported towards the PFR (tile4) (thermal decomposition)

A stable Be-C-O layer remains on tile 3

C-layer built up on the divertor floor

The layer is decomposed by plasma impact on tile 4, more effective in large Elmy shots than in L mode

See also R. Pitts, TFE report

CBe

Present view : post mortem analysis, QMB & spectroscopy

1

2

45

To investigate more:

Chemical composition and stability of Be-C-O mixed layer on PFC sides (formed after many thermal treatments on tile 1,3 )

Mechanism of ELM induced transport: erosion, ablation, decomposition

New measurements done in SCK CEN Belgium on JET inner divertor deposited layers



XPS on Be coated C tiles

First results obtained at SCK•CEN

Sven Van den Berghe, Inge Uytdenhouwen, Paul Coad

Escalab 250 surface station can handle Be and T

contaminated samples

monochromator Al K(spot 0.1 – 1 mm)

electron detectorimage detector

X-ray guntwin Al, Mg anode, ~1.2-1.4 keV

analyser (max. res. 0.018 eV)

transfer armUV lamp

camera

electron gunspatial res. ~100 nm

analysis chamberP~10-11 Bar

preparation chamber

x,y,z stage

ion gun, Ar

Be-metalBe-carbide

Be-O

Sputter XPS of JET inner deposit

Only about 1 nm sputtered

XPS results on JET tile 3

Be 1s

XPS shows large contribution of BeO with some Be2C and Be

Further XPS analysis is planned across the whole layer (cross sections, UKAEA, SEK, FZJ)

Remark: in JET the Be/O flux ratio is about 1 or below , thus Be can find enough oxygen to form BeO through the whole layer?



Used Be JET limiter & divertor tiles (1989-1992) are analysed again (M. Rubel, VR Sweden)



Be – C system: Pisces experiments

Be

C

D

Be

Issues

Be-C layer formation(Be2C)

Diffusion of C in Be2C,

Thermal stability

Influence of oxygen

Be re-erosion by D impact Thermal decomposition

Enhanced Be re-erosion (?)

Important EU-US co-operation to study the dynamics of the Be-C system (simulate ITER conditions at lower C- target )

To analyse: reduction of chemical erosion due to

Be surface coverage

change of chemistry

EU activities

Experiments and surface analysis, IPP (K. Schmid, R. Pugno)

Modelling (FZJ, Kirschenr, Borodin)



Be – C system: Pisces

Pisces data show a very promising strong reduction of carbon chemical erosion

R. Doerner PSI 17

10-3

10-2

10-1

100

0 100 200 300 400 500 600

w/o H.P. (20060322)exponential fit for w/o H.P.w/ H.P. (20060323)exponential fit for w/ H.P.

Time [s]

BeII/ne ~ 0.13 %

Be/C ~ 17 sec

Be/C ~ 83 sec

R. Pugno P 17

• Strong decrease of CD light • Pulsing to Tsurf ~ 1200-1400ºC

(so far) decreases chemical erosion mitigation time

• Be2C decomposes at ~ 2100ºC

D. Nishijima et al., PSI 17

Pisces empirical chemical erosion suppression time scaling law

tCDscale [s] = 1.0e-7 cBe+

-1.9±0.1 Ei0.9±0.3 Γi

-0.6±0.3 exp(4.8(±0.5)x103/Ts)

cBe+ Be concentration

Ei I incident ion energy,

i Plasma flux

Ts Temperature




• Further benchmarking of scaling

• Influence of higher temperature excursions

• Influence of oxygen

• Modelling (Ero- Tridyn & others): extrapolation to ITER

Ongoing cooperation with IPP and FZJ

Future Pisces tasks

• At RT, Be-rich mixed Be/C/O and C layers retain deuterium at similar levels

• Only at higher temperature (> 400-500K) Be-rich layers have significant less retention

• Codeposited Be/C layers in PISCES-B are Be rich

• Influence of oxygen to investigate more

The other critical question is the level of fuel retention in mixed co-deposited Be –C (O) layers




Ongoing work on Pisces witness probe and target post mortem analysis (Pisces, IPP)

Lab ion beam Be implantation experiments for fundamental processes (Pisces, IPP)



Be – W system

Be – W interaction is of similar critical importance for ITER

Activities

• W deposition on Be → annealing in vacuum (IPP)

• Be deposition on W → annealing (IPP)

• Be seeded Pisces plasmas on W (Pisces, IPP, FZJ )

W

A major question for the JET ITER like wall project



Be – W system

Various parameters determine the possible formation of Be-W alloys:

• Be/D flux ratio to the target (and other impurities, C,O)

• Target temperature (competition of Be-W formation with sublimation, dynamics of alloying process )

• Re-sputtering of Be from Be-W mix (Be2W) and freshly deposited Be

Further experiments and modelling ongoing

Lab work (IPP)

Cooperation with Pisces (IPP)

Modelling (IPP, FZJ , Tekes, Uni. Marseille)



W – C system

W – C interaction also important for JET wall project

C WC W

W carbide forms at interface by diffusion of C in W (temperature activated)

C diffusion in W-C much slower , reduces further carbide formation

W-C has reduced melting point and is more brittle

Guideline for JET wall project: Tmax < 1600C

More information and modelling needed

Further experiments in IPP, FZJ , Slovenia

Modelling: IPP, FZJ, Tekes



W – C system

Investigated binary carbon-metal systems:

W, Be, Fe, Ni, Ti, (Si)

• carbide monolayer at interface

• carbide formation (one or more phases) at elevated temp.

• carbon dissolution in metal bulk

C. Linsmeier at al

Existence of WC, W2C, W2B has been identified on TEXTOR W VPS layers after large temperature excursions



W – C system

New contribution from IPPLM, Association Warsaw (M. Psoda, E.Fortuna )

VPS layers on TEXTOR graphite tiles after temperature excursions: formation of a new the W-Re sigma phase

Transverse cracks along the Re/ W-Re boundary;

Carbon present between sigma W-Re and VPS tungsten coating.

Before After exposure

Fortuna et al., PhysicaScripta, submitted

Modelling activities

Surface models:

• Sputter and flux balanced models (IPP, FZJ)

• Tridyn surface models in combination with ERO (FZJ, IPP)

• MD and QM modelling of chemistry, reflection and erosion (Tekes, Uni.- Marseille )



Modelling

ERO modelling (A. Kirschner, D. Borodin. S. Droste )

PISCES: chemical erosion &beryllium co-deposition carbide formation

- TEXTOR: 13CH4 injection (graphite and W limiter) local transport of

deposited carbon, W-C mixing effects with TriDyn

- JET: net-erosion of W stripe in outer divertor

ITER modelling

- Target lifetime and tritium retention under influence of Be co-deposition

- Be limiter erosion during ramp phase



Modelling

A.Allouche et al CNRS and Université de Provence, MarseilleElectronic structure of beryllium metal surfaceGraphite surface reactivity (co-op with P. Krstic)Hydrogen retention and recombination on beryllium surfacesBeryllium - rare gases interaction (EFDA task)Beryllium on tungsten, mixed Be/W materials (R. Doerner)Carbon on/in beryllium, first steps of Be2C formation ( Linsmeier)



Modelling

MD Modelling: Nordlund, University of Helsinki

•WC mixed materials in ITER

• Main findings:

–chemical sputtering of WC even for very low H bombarding energies

–preferentially sputtering of C is bombardment of W by C and H: dynamic balance of WC formation and erosion

• Good agreement with experiments by Plank&Eckstein

Future: developing an interatomic potential for the quaternary Be-W-C-H system



Modelling



Summary and outlock

Be-C and Be-W interaction is a main task and further work important

Pisces, JET Be-C data, Lab work

Modelling (IPP, FZJ, Tekes, Un. Marseille )

(JET ILW project)

W-C system: Dynamics of W- C carbide formation

Lab data, TEXTOR and AUG data

Oxygen important residual impurity

Ternary systems

Modelling: understanding of fundamental processes and extrapolations to ITER conditions

CONCENTRATION RATIO: BERYLLIUM - TO - CARBON

1

2

3

45 6

78 9 10

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

DIVERTOR TILE (POLOIDAL DIRECTION)

Be

/ C

Inner Outer

Be/C ratio JET MKIIA divertor tiles

JET: codeposition of Be, C &O leads to (stable) Be-C-O layers on plasma viewing sides of inner tiles, while the excess of C is released and transported to shadowed areas



Be–C- O: previous JET experiences

Topics Fusion device Lab- experiment Modelling

Be-W interaction

Pisces*Be/W target interaction (spectroscopy, post mortem analysis)

IPP, MEC :Preparation of Be/W systemsCharacterisation of Be/W properties &alloy

FZJ: ERO-Tridyn for Pisces Be/W experiments IPP: mixing modellingTekes: MD modelling of erosion/deposition

Be-C interaction

JET/Tekes/VR Analysis of Be/C redeposited layers: composition, chemical state, hydrogen retentionPisces * : Be/C arget interaction (spectroscopy, post mortem analysis

IPP, MEC :Preparation of Be/C systemsCharacterisation of Be/C properties (thermal stability, H retention ,…(EFDA technology task RETMIX)

FZJ: ERO-Tridyn for Pisces Be/C experiments IPP: mixing modelling Tekes: MD modelling of erosion/deposition

W/C interaction AUG: post mortem analysis of W/C layers, in situ spectroscopyFZJ: dedicated W/C mixed material experiments in limiter locks

Slovenia Preparation of W/C mixed systems & characterisation

FZJ: ERO-Tridyn for Pisces Be/C experiments IPP: Tridyn and other mixing modellingTekes: MD modelling of erosion/deposition

Dynamics of layer formation (erosion/deposition) under multispecies impact

FZJ: dedicated multispecies mixed material experiments in limiter locks and in situ spectroscopy

IPP: Dual beam experiment FZJ: ERO-TridynIPP: Tridyn and other mixing modelling Tekes: MD modelling of erosion/deposition



Workprogramme

Documents

Report on SEWG ITER like Material Mix V. Philipps on behalf of SEWG working group* Decided during EU -TF meeting Cadarache, 2005 Work programme defined