1. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 1 Report of the Special Expert Working Group on Chemical Erosion S. Brezinsek Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Jülich, Germany SEWG members: CEA E. Gauthier, J. Hogan … CIEMAT F. Tabares … FZJA. Pospieszczyk, A. Kirschner, A. Kreter, D. Borodin, G. Sergienko, V. Philipps … IPPW. Jacob, J. Roth, Ch. Hopf, M. Mayer, M. Schlüter, T. Schwarz-Selinger R. Pugno, A. Kallenbach, W. Bohmeier … UKAEAM.F. Stamp …

2. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 2 Status: ITER - tritium inventory limit WBC, PSI 2002 Roth/Kirschner ERO, PSI 2004 600 full performance shots!

3. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 3 Flux dependence of Y chem In-situ calibration: mass/optical spectroscopy Temperature normalisation to T max Ion energy normalisation to 30 eV Flux dependence Roth et al. EPS2003, PSI 2004 Y(E,T, )= Description of Y as function of - Ion energy - Surface temperature - Ion flux Y low (E,T) 6*10 21 1+1+ 0.54

4. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 4 ERO modelling for ITER scenarios standard ITER operation Roth, Kirschner et al. NF 2004 Plasma simulation from B2 Eirene Steady-state temperature profiles along the divertor target (Federici 2003) But: No consideration of ELMs, no a-C:H layers, no synergetic effects …

5. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 5 Topics to be discussed Improvement in the data evaluation Better spectroscopic data interpretation Photon efficiencies Higher Hydrocarbons Influence of ELMs (e.g. AUG) & detached plasmas (e.g. DIII-D, JET) Geometry and strike-point positions (e.g. JET, AUG) Erosion of redeposited a-C:H layers (e.g. JET) Synergetic effects Mixed layers, Be and W (e.g. PISCES) He +, Ar + (e.g. MAJESTIX), N 2 (e.g. JET, AUG) ERO modelling Benchmark experiments (e.g. PSI-2, TEXTOR)

6. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 6 Improvement in the data evaluation Better spectroscopic data interpretation Photon efficiencies Higher Hydrocarbons Influence of ELMs (e.g. AUG) & detached plasmas (e.g. DIII-D, JET) Geometry and strike-point positions (e.g. JET, AUG) Erosion of redeposited a-C:H layers (e.g. JET) Synergetic effects Mixed layers, Be and W (e.g. PISCES) He +, Ar + (e.g. MAJESTIX), N 2 (e.g. JET, AUG) ERO modelling Benchmark experiments (e.g. PSI-2, TEXTOR) Topics to be discussed

7. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 7 Spectroscopic data interpretation Brezinsek, Pospieszczyk et al. 2004 TEXTOR pre-heatable graphite limiter New experiments with intensity corrections: Y=3.3 % at T max =830 K Previous experiments (in Roth data base) Y=4.2 % at T max =830 K Intensity correction: - Photon efficiency correction of D due to D 2 molecules - Impurity background in the CD spectrum subtracted

8. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 8 Improvement in the data evaluation Better spectroscopic data interpretation Photon efficiencies Higher Hydrocarbons Influence of ELMs (e.g. AUG) & detached plasmas (e.g. DIII-D, JET) Geometry and strike-point positions (e.g. JET, AUG) Erosion of redeposited a-C:H layers (e.g. JET) Synergetic effects Mixed layers, Be and W (e.g. PISCES) He +, Ar + (e.g. MAJESTIX), N 2 (e.g. JET, AUG) ERO modelling Benchmark experiments (e.g. PSI-2, TEXTOR) Topics to be discussed

9. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 9 Higher Hydrocarbons Vignettation l-o-s Y C2H4 3.0 % JET: C 2 light from C 2 H 4 injection t / s Higher hydrocarbons only partially treated! Brezinsek, Stamp 2004

10. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 10 Improvement in the data evaluation Better spectroscopic data interpretation Photon efficiencies Higher Hydrocarbons Influence of ELMs (e.g. AUG) & detached plasmas (e.g. DIII-D, JET) Geometry and strike-point positions (e.g. JET, AUG) Erosion of redeposited a-C:H layers (e.g. JET) Synergetic effects Mixed layers, Be and W (e.g. PISCES) He +, Ar + (e.g. MAJESTIX), N 2 (e.g. JET, AUG) ERO modelling Benchmark experiments (e.g. PSI-2, TEXTOR) Topics to be discussed

11. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 11 Plasma regimes – H-mode in AUG Pugno et al. PSI 2004 There is an ion flux dependence in H-mode discharges Data not normalised! with ELMs Integrated over ELMs!

12. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 12 Detached plasmas: still large uncertainties, big scatter of data -> DIII-D practically no chemical erosion (Whyte et al NF 2001) -> JET inner divertor: 15% erosion (strike point on vertical target), less on horizontal target (Stamp 2003) -> AUG … -> TEXTOR test limiter: increase of C 2 signal! Higher erosion Effect of rate coefficients? (Pospieszczyk EPS 1995) New experiments necessary! High flux and low energy should reduce the erosion yield! Plasma regimes – detachment

13. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 13 Geometry and strike-point positions Esser et al. PSI 2004 Strike-point position important Stepwise transport of carbon QMB – deposition monitor

14. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 14 Improvement in the data evaluation Better spectroscopic data interpretation Photon efficiencies Higher Hydrocarbons Influence of ELMs (e.g. AUG) & detached plasmas (e.g. DIII-D, JET) Geometry and strike-point positions (e.g. JET, AUG) Erosion of redeposited a-C:H layers (e.g. JET) Synergetic effects He +, Ar + (e.g. MAJESTIX) on a-C:H layers, N 2 (e.g. JET, AUG) Mixed layers, Be and W (e.g. PISCES) ERO modelling Benchmark experiments (e.g. PSI-2, TEXTOR) Topics to be discussed

15. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 15 Sweep of the strike point through the corner in L-mode a-C:H layers in the inner divertor of JET Brezinsek et al. PSI 2004 Strong C 2 light emission from hydrocarbon layers => C 2 D y Different ratio of C 2 to CD light Removal within one discharge in H-mode with strike-point fixed at the location of the layer a-C:D layer strike point 14.3 s 14.7 s 15.0 s ch3

16. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 16 a-C:H layers in the inner divertor of JET Strike point fixed at the location of the a-C:D layer Three identical discharges with L- and H-mode phase Removal of a (soft) a-C:D layer / main release product: C 2 D y Base value indicates bulk material or a different type of a-C:D layer (=> Planck radiation – M.F. Stamp P3-50) QMB (deposition monitor near the inner divertor louvre): 1st: strong deposition (~30 nm) 2nd & 3rd: slight erosion KME narrow channel: 1st: strong C 2 light emission 2nd: 55% reduction of C 2 light

17. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 17 Different gas injection in the later phase of the discharge! Repetition of six discharges with strike point sweep in L-mode a-C:H layers in the inner divertor of JET Net-erosion? Brezinsek et al. PSI 2004

18. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 18 Improvement in the data evaluation Better spectroscopic data interpretation Photon efficiencies Higher Hydrocarbons Influence of ELMs (e.g. AUG) & detached plasmas (e.g. DIII-D, JET) Geometry and strike-point positions (e.g. JET, AUG) Erosion of redeposited a-C:H layers (e.g. JET) Synergetic effects He +, Ar + (e.g. MAJESTIX) on a-C:H layers, N 2 (e.g. JET, AUG) Mixed layers, Be and W (e.g. PISCES) ERO modelling Benchmark experiments (e.g. PSI-2, TEXTOR) Topics to be discussed

19. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 19 UHV chamber Setup MAJESTIX H2H2 CH 3 N 2 (CH 3 ) 2 ellipsometry, infrared substrate preparation chamber rf plasma H Wien Filter Ar + 1 keV Ar + 20 eV de- celeration UHV experiment with 2 radical beam sources and one ion beam source W. Jacob, Ch. Hopf, A. von Keudell, M. Meier, and T. Schwarz-Selinger: Particle-beam Experiment to Study Heterogeneous Surface Reactions Relevant to Plasma-assisted Thin Film Growth and Etching, Review of Scientific Instruments 74, 5123-5136 (2003). Synergetic effects – Ion beam and H

20. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 20 Combined interaction of ions with atomic H leads to chemical sputtering here: ratio H/ion = 400 strongly enhanced erosion Ch. Hopf, A. von Keudell, and W. Jacob, Chemical Sputtering of Hydrocarbon Films, J. Appl. Phys. 94, 2373 (2003). Modeling results: Ch. Hopf and W. Jacob, unpublished,N 2 data: M. Meier et al., unpublished atomic H + ions Model parameters: a = 0.4 R 400 Status: TW4-TPP-ERCAR Intermediate Report Jan. 2004 Synergetic effects – chemical sputtering on hard a-C:H layer

21. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 21 Model parameters: a = 0.4 R 400 Ch. Hopf, A. von Keudell, and W. Jacob, Chemical Sputtering of Hydrocarbon Films, J. Appl. Phys. 94, 2373 (2003). Modeling results: Ch. Hopf and W. Jacob, unpublished Predictions of the chemical sputtering yields for various fusion relevant species based on the model by Hopf et al. Status: TW4-TPP-ERCAR Intermediate Report Jan. 2004 Energy dependence – modelling

22. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 22 M. Schlüter, unpublished Chemical sputtering yield for the simultaneous interaction of H and Ne + Good agreement with the model by Hopf et al. Status: TW4-TPP-ERCAR New results Synergetic effects – new results

23. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 23 Erosion was measured in low- temperature ECR plasmas in mixtures of N 2 and H 2 (p = 1 Pa). The ion energy was varied by applying an rf bias to the sample electrode. Steep increase of erosion rate with increasing N 2 admixture (factor 15). Maximum for 20 to 30 % N 2. Slow decrease from 30 to 100 % N 2. Sun Chao, Ch. Hopf, T. Schwarz-Selinger, and W. Jacob, unpublished Status: TW3-TPP-SCAVOP New results New results: Erosion in N 2 /H 2 plasmas Scavenger experiments performed by Tabares in JET, ASDEX, PISCES => see CIEMAT

24. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 24 Expose C target to Be seeded D plasma, Target Bias 50V Increase Be concentration from 0.0 to 0.15 % during exposure Monitor Be 1+ line and CD-band Target temperature ~ 500K high chemical erosion Expose C target to Be seeded D plasma, Target Bias 50V Increase Be concentration from 0.0 to 0.15 % during exposure Monitor Be 1+ line and CD-band Target temperature ~ 500K high chemical erosion CD-band decreases by ~80% for a Be plasma concentration of 0.15 % Be surface coverage after exposure 87% (AES). Indicates shielding effect through Be layer formation Synergetic effects – Be and C Schmidt et al. PSI 2004 0.000.050.100.15 0 20 40 60 80 100 CD-Band intensity [%] Be plasma concentration [%] CD-Band intensity [%] Linear Fit: CD = 100.0 - 580.6 * C Be

25. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 25 Be surface concentration increases quickly with Be plasma concentration Expose C targets to a Be seeded D plasma at: At target temperatures from ~500K to ~1280K Be plasma concentrations from 0 to 0.35 % Measure (AES) Be surface concentration after exposure At temperatures 1200K diffusion and thermally enhanced erosion reduce Be surface coverage Almost full surface coverage for Be plasma concentrations < 1% Schmidt et al. PSI 2004 Synergetic effects – Be and C

26. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 26 Improvement in the data evaluation Better spectroscopic data interpretation Photon efficiencies Higher Hydrocarbons Influence of ELMs (e.g. AUG) & detached plasmas (e.g. DIII-D, JET) Geometry and strike-point positions (e.g. JET, AUG) Erosion of redeposited a-C:H layers (e.g. JET) Synergetic effects He +, Ar + (e.g. MAJESTIX) on a-C:H layers, N 2 (e.g. JET, AUG) Mixed layers, Be and W (e.g. PISCES) ERO modelling Benchmark experiments (e.g. PSI-2, TEXTOR) Topics to be discussed

27. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 27 ERO modelling - Parallelisation of ERO code - Improvement of surface model for material mixing (TriDyn) - Merging of various versions (limiter – divertor – linear devices) - Including global transport for divertor devices, code coupling?? - Modelling: transport of injected hydrocarbons – TEXTOR, JET, AUG (D/XB, deposition efficiency, re-erosion of deposits) chemical erosion studies (Roth formula, JET, ITER) PISCES (Be-C layers, tungsten) formation of mixed layers (dedicated experiments at TEXTOR)

28. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 28 Example: ERO modelling for ITER Erosion & re-deposition along outer target: Roth vs. 1% yield Sticking = 0 for hydrocarbons, MolDyn for atoms Gross erosion 10 times larger with fixed 1% than Roth yield. Local re-deposition significantly smaller with fixed yield. with Roth yield: 94% re-deposition 6% loss to PFR with fixed yield: 80% re-deposition 20% loss to PFR

29. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 29 ERO modelling – PSI-2 experiments comparison of databases (Erhardt & Langer; Alman, Ruzic & Brooks, Janev & Reiter) check of sticking coefficients in-situ study of erosion and deposition Bohmeyer et al. PSI2004

30. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 30 Future work Improvement in the data evaluation Erosion yield for higher hydrocarbons Extension of the plasma parameter regime (detached plasmas) erosion of redeposited layers (a-C:H layer) Synergetic effects effect of mixed layers, Be and C Chemical erosion He+, N 2 + - H mixtures ERO Modelling TEXTOR and JET methane puffs an hydrocarbon transport, D/XB values, higher hydrocarbons, PISCES sticking coefficients, data base, PSI-2

31. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 31 Online manual on ERO webpage

32. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 32 Further plans TW4-TPP-ERCAR: Measurement of Chemical Sputtering yields for He + + H (experiment MAJESTIX) TW3-TPP-SCAVOP: Measurement of Chemical Sputtering yields for N 2 + + H (experiment MAJESTIX) Investigation of gas phase chemistry for the plasma surface interaction of N 2 /H 2 gas mixtures with hydrocarbon surfaces in low-temperature laboratory plasma experiments (PLAQ and PAUKE) Investigation of deposition in CH 4 plasmas with increasing N 2 admixture (experiment PLAQ)

33. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 33 Normalisation T max Roth et al. EPS2003, PSI 2004 TEXTOR: Y=4.2 % at T max =830 K

34. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 34 Spectroscopic data interpretation Brezinsek, Pospieszczyk 2004 TEXTOR pre-heatable graphite limiter Intensity correction: - Photon efficiency correction of D due to D2 molecules - Background in the CD spectrum

35. EU Plasma-Wall Interaction TF – Meeting 14.10.04 - FZJ SEWG Chemical Erosion S. Brezinsek TEC 35 IPP contributions to SEWG Chemical Erosion: Plasmatechnology group Ch. Hopf, W. Jacob, M. Schlüter, and T. Schwarz-Selinger Max-Planck-Institut für Plasmaphysik, 85748 Garching Content: The experiment MAJESTIX Chemical Sputtering of hydrocarbon layers Ar + + H (older data and model predictions) Ne + + H (new results) Erosion in N 2 /H 2 plasmas Further Plans