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 V.Philipps, EU TF Meeting, Slovenia, Nov 2006

for the ITER like material mix …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 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….. V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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 V.Philipps, EU TF Meeting, Slovenia, Nov 2006 The most important topics

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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)

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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 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, Be 2 C fully formed, D is thermally released V.Philipps, EU TF Meeting, Slovenia, Nov 2006 heating C D C D C Be no significant carbon dissolution in bulk stable surface carbide at elevated temp. C on Be (with O)

Oxidation is determined by diffusion of Be through BeO, (confirmed by 16,18 O isotope experiments ) V.Philipps, EU TF Meeting, Slovenia, Nov 2006 O on Be Oxide layer before Oxide layer after No significant reaction at 375 C oxidation starts not before 400C Be BeO O2O2 Oxidation of Be in O 2 ( 660mbar )

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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 Be 2 C ( C. Linsmeier)

Atomic oxygen: interaction with binary metal-C systems and ternary metalCO systems BeW system: reaction kinetics of alloy formation reactivities with C, O Hydrogen inventory: clean and oxide/carbide covered beryllium tungsten systems (W, BeW) BeW 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 (mm) More BeO More Be 2 C P. Coad et al, Journ. Nucl. Mat. 176 & 177 (1990) 145 V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Be–C- O: previous JET experiences Be 2 C 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 C Be Present view : post mortem analysis, QMB & spectroscopy

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 V.Philipps, ITPA Toronto 2006

XPS on Be coated C tiles First results obtained at SCKCEN 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 detector image detector X-ray gun twin Al, Mg anode, ~ keV analyser (max. res eV) transfer arm UV lamp camera electron gun spatial res. ~100 nm analysis chamber P~ Bar preparation chamber x,y,z stage ion gun, Ar

Be-metal Be-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 Be 2 C 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? V.Philipps, ITPA Toronto 2006

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

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Be – C system: Pisces experiments Be C D Issues Be-C layer formation(Be 2 C) Diffusion of C in Be 2 C, 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)

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Be – C system: Pisces Pisces data show a very promising strong reduction of carbon chemical erosion R. Doerner PSI 17 R. Pugno P 17 Strong decrease of CD light Pulsing to T surf ~ ºC (so far) decreases chemical erosion mitigation time Be 2 C decomposes at ~ 2100ºC

D. Nishijima et al., PSI 17 Pisces empirical chemical erosion suppression time scaling law t CD scale [s] = 1.0e-7 c Be+ -1.9±0.1 E i 0.9±0.3 Γ i -0.6±0.3 exp(4.8(±0.5)x10 3 /T s ) c Be+ Be concentration E i I incident ion energy, i Plasma flux T s Temperature V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Be – C system: Pisces 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 (> K) 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 V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Be – C system: Pisces Ongoing work on Pisces witness probe and target post mortem analysis (Pisces, IPP) Lab ion beam Be implantation experiments for fundamental processes (Pisces, IPP)

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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 (Be 2 W) and freshly deposited Be Further experiments and modelling ongoing Lab work (IPP) Cooperation with Pisces(IPP) Modelling(IPP, FZJ, Tekes, Uni. Marseille)

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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: T max < 1600C More information and modelling needed Further experiments in IPP, FZJ, Slovenia Modelling: IPP, FZJ, Tekes

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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, W 2 C, W 2 B has been identified on TEXTOR W VPS layers after large temperature excursions V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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 ) V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Modelling

ERO modelling (A. Kirschner, D. Borodin. S. Droste ) PISCES: chemical erosion &beryllium co-deposition carbide formation - TEXTOR: 13 CH 4 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 V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Modelling

A.Allouche et al CNRS and Université de Provence, Marseille Electronic structure of beryllium metal surface Graphite surface reactivity (co-op with P. Krstic) Hydrogen retention and recombination on beryllium surfaces Beryllium - rare gases interaction (EFDA task) Beryllium on tungsten, mixed Be/W materials (R. Doerner) Carbon on/in beryllium, first steps of Be 2 C formation ( Linsmeier) V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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 V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Modelling

V.Philipps, EU TF Meeting, Slovenia, Nov 2006 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

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 V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Be–C- O: previous JET experiences

TopicsFusion deviceLab- experimentModelling Be-W interaction Pisces* Be/W target interaction (spectroscopy, post mortem analysis) IPP, MEC : Preparation of Be/W systems Characterisation of Be/W properties &alloy FZJ: ERO-Tridyn for Pisces Be/W experiments IPP: mixing modelling Tekes: MD modelling of erosion/deposition Be-C interaction JET/Tekes/VR Analysis of Be/C redeposited layers: composition, chemical state, hydrogen retention Pisces * : Be/C arget interaction (spectroscopy, post mortem analysis IPP, MEC : Preparation of Be/C systems Characterisation 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 interactionAUG: post mortem analysis of W/C layers, in situ spectroscopy FZJ: 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 modelling Tekes: MD modelling of erosion/deposition Dynamics of layer formation (erosion/depositi on) under multispecies impact FZJ: dedicated multispecies mixed material experiments in limiter locks and in situ spectroscopy IPP: Dual beam experimentFZJ: ERO-Tridyn IPP: Tridyn and other mixing modelling Tekes: MD modelling of erosion/deposition V.Philipps, EU TF Meeting, Slovenia, Nov 2006 Workprogramme