1. 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

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

3. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 YearAssociate(s)Baseline Support (ppy) Priority Support (ppy) remarks 2008PWI-08-TA-08/FZJ/PS/00 Task Coordinator : V. Philipps FZJ3/12 PWI-08-TA-08/CEA/BS/01 Molecular dynamic simulations of mixed materials CEA6/12 PWI-08-TA-08/FZJ/BS/01 ERO-modelling of PISCES-B results. Coupling of ERO with SDTrimSP FZJ5/12 Report (SEWG meeting) PWI-08-TA-08/FZJ/PS/01 ERO-modelling of mixed materials (ITER application) FZJ2/12 Report (SEWG meeting) PWI-08-TA-08/FZJ/BS/02 Analysis of mixed W-C layer formation in gaps of ITER like castellated W targets FZJ3/12 Report (SEWG meeting) PWI-08-TA-08/IPP/BS/01 Binary and ternary systems (Be, C, O, W), kinetic simulation of material mixing IPP36/12 Report (SEWG meetin) PWI-08-TA-08/IPP/PS/01 Joint investigation of fuel retention in Be-C/W layers 6/12 PWI-08-TA-08/IPP/BS/02 Dual beam experiment D+C on W IPP10/12 Report (SEWG meeting) PWI-08-TA-08/IPPLM/BS/01 Post mortem analysis of mixed layers formation: TEM, FIB, SEM, EPMA, XRD, AES etc IPPLM4.5/12 Report Workprogramme 2008

4. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 PWI-08-TA-08/IPPLM/BS/01 Post mortem analysis of mixed layers formation: TEM, FIB, SEM, EPMA, XRD, AES etc IPPLM4.5/12 PWI-08-TA-08/IST/BS/01 Characterization of samples IST/ISN2/12 No samples delivered PWI-08-TA-08/MEDC/BS/01 Preparation of mixed Be-C&W layers and analysis of retention MEdC12/12 Report (SEWG meeting) PWI-08-TA-08/SCK/BS/01 Refurbishment of the plasmatron VISION I SCK-CEN3/12 Report (SEWG meeting) PWI-08-TA-08/TEKES/BS/01 MD modelling of mixed layers (W, Be), TEKES18/12 Report (SEWG meeting) PWI-08-TA-08/VR/BS/01 Post mortem analysis mixed layer formation VR5/12 Report (SEWG meeting) PWI-08-TA-08/VR/PS/01 Post mortem analysis mixed layer formation on PFC in TEXTOR and other EU devices VR2.4/12 Report (SEWG meeting) Total104.5/1213.4/12

5. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Vessel Walls 1. High flux case 1x10 24 /s (Tokamak experience) 2. Low flux case 1x 10 23 /s ( B2-Eirene estimate) 2% Be erosion case 1: 50% dep. in main chamber 37.5% dep. in inner divertor 15.5% dep. in outer divertor case 2: 75% dep. in inner divertor 25% 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 3x10 24 /s Impurity flux distribution from Divimp ( K. Schmid) Divertor erosion deposition: ERO code with Divimp distribution, matched to the total impurity fluxes

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

7. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Recent results from Pisces (EU-Pisces cooperation )

8. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 EU-Pisces cooperation 1. 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)

9. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 For Beryllium: For Tungsten For Carbon D/C = 0.0204 E –0.43 ( D / C ) 0 exp (2268/T c ) 293 < T c < 473 K 473 < T c < 973 K 15 < E < 100 eV D / C < ? large 293 < T c < 600 K 15 < E < 62 eV D / Be < 2000 293 < T c < 600 K 60 < E < 280 eV D / W < 500 Models overlap: 293 - 600K ~60 eV ~10s - 1000s flux ratios D/Be = (5.82 x 10 -5 )E n 1.17 0.2 ( D / Be ) -0.21 0.1 exp (2273 311/T c ) D/W = (5.13 x 10 -8 )* E n 1.85 0.4 * ( D / W ) 0.4 0.1 * exp (736 228/T c ) 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

10. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Roth PPCF 2008 Retention levelScaling (523K, 20eV, D / X =100) Scaling (523K, 60eV, D / X =100) 0.6(D+T)/C0.40.3 0.03(D+T)/Be0.050.2 0.002(D+T)/W0.00030.003 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 R. Dörner, SEWG meeting, 9-10.10. 2008

11. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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) R. Dörner, SEWG meeting, 9-10.10. 2008

12. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Topic: chemical erosion of Be-C mixed system R. Dörner, SEWG meeting, 9-10.10. 2008 Present data: a small beryllium impurity concentration in the plasma drastically suppresses carbon erosion with a characteristic decay time

13. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 CD band decay time similar with and without argon R. Dörner, SEWG meeting, 9-10.10. 2008 Addition of Ar to the plasma does not affect the mitigation of carbon chemical erosion by beryllium

14. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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 D 2 plasma. A thin layer of Be as little as a few 10s of nm suppress blister formation and D retention. R. Dörner, SEWG meeting, 9-10.10. 2008

15. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Mixing He with D-plasma suppresses also blisters on W surface and reduces D-retention in W. Pure D 2 plasma (SRWM-3b) D-fluence ~ 5e25 m -2, D ~ 1.0e22 m -2 s -1, T s ~ 573 K, E i ~ 60 eV D 2 -He mixture plasma (SRWM-4b) D-fluence ~ 5e25 m -2, D ~ 0.9e22 m -2 s -1, T s ~ 573 K, E i ~ 50 eV, n He+ /n e ~ 20 % R. Dörner, SEWG meeting, 9-10.10. 2008 Similar new results by Alimov et al

16. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Topic: development of surface nanostructures Nano-morphology develops only above 900 K. T s = 1120 K, He+ = 4–6×10 22 m –2 s –1, E ion ~ 60 eV Fluence R. Dörner, SEWG meeting, 9-10.10. 2008

17. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Observed t 1/2 proportionality. The thickness of the nano- structured layer, d, agrees well with =(2Kt) 1/2, with, K 1120 K = 6.6 0.4 10 –16 m 2 s –1 K 1320 K = 2.0 0.5 10 –15 m 2 s –1 Overall process is consistent with an activation energy of ~0.7 eV. Nanostructures are observed on various W materials, also doped W materials

18. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 In D2He 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 BeW alloy or He induced nano-morphology – Be and/or He may alleviate also W blistering. at W strike-points (T above 1000 K). – BeW alloy and/or He induced nano- morphology can develop !!

19. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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 Local saturation of available binding sites Local saturation of available binding sites Trapping in ion induced defects C. Linsmeier, SEWG meeting, 9-10.10. 2008 Topic: T retention in bulk Be

20. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 [E S = -0.10 eV] Atomic D E 0 0 [ΔE Ad = 0.87 eV] Molecular D 2 [E BE (1/2 D 2 ) = -2.278 eV] Surface Mobile state [ΔE D = 0.29 eV] E (D-Atom) Activation energies obtained from modeling of TPD spectra Temperature [K] Desorption rate [a.u.] ΔE = 1.25 eV 1.33 eV ΔE = 1.9 eV 2.1 eV (simple model) Ion-induced defects Supersaturated states C. Linsmeier, SEWG meeting, 9-10.10. 2008

21. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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) C. Linsmeier, SEWG meeting, 9-10.10. 2008

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

23. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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. 2008 PWI-08-TA-08/FZJ/BS/02 Poloidal gaps

24. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Low W fraction detected in the deposits: W fr.max <10 at.% Large differences of W intermixing in toroidal and poloidal gaps W mixing in toroidal gaps D=5.51 C= 20.4 D/C=2.7 D=0.98 C=13.4 D/C=0.73 D=3.29 C=25.3 D/C=1.3 W fr.max 4% D=10.09 C=19.9 D/C=5.5 W fr.max 4% D=9.68 C=44.8 D/C=0.38 W fr.max 10% D=1.07 C=28.2 D/C=2.16 W fr.max 10% D=3.26 C=39.8 D/C=0.82 W fr.max 5% D= 15.8 C=28.2 D/C=5.6 W fr.max 5% BtBt Left of field line direction Right of field line direction Geometry and plasma impact effect Under analysis

25. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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 (200 o C) layerD (at%) Be (at%) 12 C (at%) 13 C (at%) O (at%) 132557312 23532519 33225915 4146448 5619696 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

26. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 layerD (at%) Be (at%) 12 C (at%) 13 C (at%) O (at%) 1180.557915 21636813 31536813 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

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

28. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 No or very little deuterium detected in bulk beryllium. Small amount of co- deposited deuterium with carbon on all surfaces of Be belt limiters. C D (castellation) / C D (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. M. Rubel, SEWG meeting, 9-10.10. 2008

29. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 X W carbides and borides found Deuterium only with carbon Amount of D in W: < 5x10 14 cm -2 Side wall analysis Main phases: Graphite and W carbide: WC Traces: Tungsten and Tungsten carbide: W 2 C The same phases found in all analysed points on both sides of limiter block. W2CW2C W2CW2CW2CW2C W C C C WC 35 45 40 50 55 10 1 10 3 10 2 3x10 3 2 scale Intensity [ sqrt scale ] TEXTOR VPS poloidal W limiters Side wall M. Rubel, SEWG meeting, 9-10.10. 2008

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

31. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 AES examinations (Microlab 350) Tile 1 (outer divertor) SEM image of the tile topography and AES spectrum from position 1 Results of point analyses PositionC. at.%W at.%O at.% P1325410 P3394912 P435605 1 3 4 W-C intermixing observed

32. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Surface morphology Tile 2 ( inner divertor) deposit disclosed tungsten coating Compact, glassy-like layer of deposit Stratified character of deposit layer 50 m25 m 5 m10 m

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

34. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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. 2008 PWI-08-TA-08/IPP/BS/02

35. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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 PWI-08-TA-08/IPP/BS/02

36. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 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 PWI-08-TA-08/IPP/BS/01

37. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Be C C W W Be 2 W + Desorption Be 12 W (Be-Diffusion) W 2 C and WC (C-Diffusion) Substrate Layer Current Experiments Be 2 C (Be-Diffusion)

38. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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 F. Kost, C. Linsmeier SEWG meeting, 9-10.10. 2008

39. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 elem. C excess of Cexcess of Be XPS data F. Kost, C. Linsmeier SEWG meeting, 9-10.10. 2008

40. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Carbide formation at RT at both interfaces Be 2 C phase dominating formation at 770 K dissociation at 1070 K Be desorbs / dissolves in W C forms tungsten carbides Remaining Be diffuses to the substrate Be 2 W formation at T > 670 K Be 2 W loss at 1070 K W 2 C formation at T > 1070 K WC formation at T > 1170 K F. Kost, C. Linsmeier SEWG meeting, 9-10.10. 2008

41. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Lab study of the ternary system Be-O-W (thin Be-Layers on different Tungsten Oxides ( WO 2 and WO 3-x ) heating from 300 °C – 1000 °C in steps of 100 °C for 30 min C. Linsmeier SEWG meeting, 9-10.10. 2008

42. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 673 K, 773 K, 873 K: Decay of BeWO 3 973 K: Formation of BeWO 1073 K, 1173 K, 1273 K: Decay of BeWO 4 Be on WO 3 : Main Reactions Be on WO 2 In contrast to WO 3, tungsten dioxide does not react much with beryllium WO 2 first shows a real reaction at its dissociation temperature of 1273 K Explained by different structure of WO 3 ( more open porosity) compared with WO 2 C. Linsmeier SEWG meeting, 9-10.10. 2008

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

44. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 ERO Modelling of Erosion and Deposition of Mixed Materials: PISCES-B & ITER ( A. Kirschner, D. Borodin) Modelling of the chemical erosion of C during Be deposition in Pisces no Be-C carbide formation with Be-C carbide formation A. Kirschner, SEWG meeting, 9-10.10. 2008

45. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 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 A. Kirschner, SEWG meeting, 9-10.10. 2008 Importance of additional processes surface roughness effects inhibition of chemical erosion of a large number of C atoms

46. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Status of ERO Modelling for ITER: implementation of new T/ Be,C retention scaling for mixed layers Example Inner target: resulting (T+D)/Be and (T+D)/C A. Kirschner, SEWG meeting, 9-10.10. 2008

47. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 on targetremote berylliumcarbonberylliumcarbon (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 outer0.90.170.20.270.020.8 inner6.01.30.020.1 Revised estimated T retention rates A. Kirschner, SEWG meeting, 9-10.10. 2008

48. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Status of the plasmatron VISION 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 2008 explanation 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

49. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 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 (?)

50. V.Philipps, SEWG mixed materials, EU PWI meeting Frascati, Oct 2008 Most critical issue (from present view ) Development of W surface structures and/or Be-W compounds in the T range 800-1300K