1. ERO modelling of local 13 C deposition at the outer divertor of JET M. Airila, L. Aho-Mantila, S. Brezinsek, P. Coad, A. Kirschner, J. Likonen, D. Matveev, M. Rubel, J. Strachan, A. Widdowson, S. Wiesen and JET EFDA Contributors

2. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 2 Contents Experiment Geometry Plasma backgrounds (EDGE2D) Results Time evolution of net deposition Deposition patterns Comparison to SIMS profiles Spectroscopy Effect of ELMs Summary and outlook

3. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 3 Overview ERO modelling has been carried out for JET and AUG 13 C divertor injection experiments, which both are characterized by: injection in outer divertor SOL at the end of campaign similar magnetic geometry For JET a comprehensive 2D modelling study of global migration was carried out (J. Strachan) Interchange of data between ERO and EDGE2D modelling The AUG experiment series has been continued and modelling for later injections is in progress (L. Aho-Mantila & IPP)

4. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 4 Characteristics of the JET injection experiment Measurements of the deposition along poloidal and toroidal lines Deposition found at different poloidal locations (i.e. also outside outer divertor target) The injection is rather diffuse and toroidally distributed Brings uncertainty to quantitative estimates Puffing rate per injector is higher than in recent AUG experiments Leakage to the top of baffle 15 to 50% of injection [J. Strachan] The gas enters the vessel through a shadowed area Modelling the deposition in shadow with the 3DGap code (D. Matveev, FZJ)

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6. 6 G7B 1 2 3 4 5 6 7 8 0a0a 1a1a J. Likonen

7. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 7 Simulation geometry Simulation volume 75cm x 16cm x 16cm (t x p x r) Most of the volume in PFR Target plate approximated with an almost planar surface (realistic tile geometries will be implemented next)

8. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 8 Reference case for modelling A set of simulation parameters was defined as the basis for all parameter variations. All basic features of ERO (sputtering, reflection, diffusion, thermal force etc.) switched on Effective sticking for hydrocarbons S = 0 Carbon atoms and ions: TRIM reflection Enhanced re-erosion of deposits – factor 10 to graphite Shadowed area on tile surface: defined as a low-flux zone in plasma background Injection of CH 4 at two locations, periodic boundary in toroidal direction Interaction depth 5 nm, time step 0.005 s 2cm shift in separatrix location

9. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 9 EDGE2D plasma background: n e Inter-ELMELM-peak Shadow

10. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 10 EDGE2D plasma backgrounds: T e Inter-ELMELM-peak

11. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 11 Flux profiles Injection relatively close to separatrix High relative flux variations in simulation (injection vs. background flux) Slows down simulation Separatrix position shifted by 2cm from EDGE2D solution

12. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 12 Time evolution of net deposition: reference case

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15. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 15 Local deposition in ERO vs. experiment SIMS: 10.9% of C-13 on tile 7 and 6.1% on tile 8 [Coad et al. JNM 363-365, 287 (2007)]. Leakage 1550% [Strachan NF 2008] (10.9% + 6.1%) / (0.50.85) = 2034% - Reference case assumes re-erosion of deposits 10 times enhanced compared to graphite (i.e. E = 10) - Deposition is smaller than in experiment - With no enhancement the deposition is higher than in experiment - Match to experiment is achieved with E = 2.57 (earlier studies find match with E = 35) - Other uncertainties in the experiment than the leakage have been neglected

16. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 16 Deposition patterns Reference case No shadow

17. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 17 Deposition patterns No enh re-erosion Sticking S = 0.7

18. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 18 Comparison to SIMS (Points: SIMS, lines: ERO) Reference case No shadow No enhanced re-erosion Sticking S = 0.7

19. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 19 Assumption of injection as atoms in EDGE2D Atomic injection Simulations will be run with injection as atomic carbon @ 0.05 eV and 1 eV It has been found that the typical reflection probability of atoms is 0.3 For comparison a methane injection case with S = 0.7 was run Analysis ongoing Change in deposition pattern seems significant in the higher injection energy case

20. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 20 ELM effects – about modelling On top of the equilibrium obtained with the inter-ELM plasma background, successive ELM-peak and inter-ELM time steps were run (about 150 cycles)

21. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 21 ELM effects – erosion and deposition Net erosion occurs during ELM-peak, net deposition between ELMs Time evolution towards a new surface equilibrium, which does not differ very much from the initial surface state Initial equilibrium net deposition value = 16.9% ELMs on => 8% (transient) New equilibrium at 16.2%

22. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 22 ELM effects – resulting deposition Deposition profiles after ELMsBefore (= reference case)

23. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 23 Comparison modelling vs. spectroscopy will be done KT3: 12 radially separated channels

24. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 24 Gap model interfaced with ERO Monte Carlo code 3DGap [FZ Jülich]: flexible geometry, different physical models more realistic distribution of injected methane also traces particles provided back by ERO 13 C deposition along surfaces inside the gap Work in progress Iterations 3DGap ERO 3DGap …) Source points in ERO continues periodically… toroidal

25. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 25 Preliminary estimations from 3DGap point sources in ERO for methane injection sticking of hydrocarbon according to literature, no erosion ~45-70% of injected particles return to the gap (ERO) ~35-75% of these particles can be trapped in the gap (3DGap) iterations increase of re-deposition inside the gap >15% of puffed 13 C amount might be trapped inside the gap

26. VTT TECHNICAL RESEARCH CENTRE OF FINLAND 26 Summary Detailed modelling of 13 C local deposition in 2004 JET injection experiment has been carried out The ERO + simple gap model reproduces measurements closely using the assumptions Effective sticking on hydrocarbons S = 0 Re-erosion of reposited carbon is enhanced by the factor E ~ 2.5–7 Tile gap will be modelled in more detail with the 3DGap code