1. 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 Introduction SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid

2. 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

3. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid 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 systems Be-W-C system (IPP lab experiments) Mixed Be/C/O layer formation in (JET) D retention in mixed materials D 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

4. 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 - PISCES Long term visits Modelling K. SchmidERO (A. Kirschner, D. Borodin) R. PugnoK. Schmid next: A. Kreter + hard ware, post mortem surface analysis SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid EU-Pisces cooperation

5. WBe Be-flux: f Be * Г D D- flux : Г D Re-eroded Be flux: Г D * Y D (Plasma temperature) Be D Evaporated Be flux: Г Be evap (Surface temperature) Be diffusion in W (Surface temperature) SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid Determining parameters Be flux ratio, Be re-erosion, Be evaporation, Be diffusion in W Be on W

6. Be-W allows form effectively in the temperature range 850-1300K. (e.g. a 0.3 mm Be 12 W layer forms at 1070K, 10eV, 0.3% Be in 1h exposure (10 26 D/m 2 ) 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 SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid Be on W: summary Pisces R. Doerner et al

7. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid Be on W: summary Pisces R. Doerner et al

8. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid Be on C: IPP lab experiments substrate Evaporation (5 10 16 /cm 2 ) crucible Be, C XPS Annealing Principle of experiments C. Linsmeier et al

9. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid first additional Be 2 C after 773 K indications for island growth 5 x10 16 Be deposited on C, Be 1s intensity metallic carbidic Transition to Be 2 C between 670 and 770K Be on C: IPP lab experiments C. Linsmeier et al

10. 69,6% 2,3% 36% 2,5% 41,6% 3,0% 27,3% 3,5% open gap shadowed gap Plasma- 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 SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid TEXTOR gap deposition experiments A. Litnovsky et al W-fraction

11. Mixture of Be, C, W 970 K C Be W SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid C. Linsmeier, F. Kost et al W 2 C amount Be 2 C amount Full Be 2 C formation: 560 K (increasing with depth) Formation of W 2 C (decreasing with depth) Small amount of WC at T > 1170 K No Be 2 C at T > 1170 K Lab data: Ternary systems

12. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid mitigation of chemical erosion of C by Be- deposition Time (s ) 0500100015002000 0.1 1 0.18 % Be 0.41 % Be 0.13 % Be 1.10 % Be 0.03 % Be Norm. CD Band strength [a.u.] Modelling with flux models and ERO Tridyn Optimise predictions for ITER divertor C- erosion Modelling A. Kirschner, D. Borodin

13. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid 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

14. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid Be-Flux fraction in EQ Global Be erosion deposition modeled based on B 2 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 Be surface concentration in EQ Peak layer growth 0.03nm/s Dome Be- deposition by re- erosion Global ITER modelling K.Schmid et al

15. 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 SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid K.Schmid et al Global ITER modelling

16. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid 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 10 17 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

17. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid 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%)

18. SEWG mixed materials EU PWI TF V. Philipps, EU PWI TF meting, Oct 2007, Madrid 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