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Recent C-MOD, NSTX, and Supercomputing Plasma/Material Interaction (PMI) Modeling

Recent C-MOD, NSTX, and Supercomputing Plasma/Material Interaction (PMI) Modeling. J.N. Brooks, J.P. Allain Purdue University PFC Meeting UCLA, August 4-6, 2010.

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Recent C-MOD, NSTX, and Supercomputing Plasma/Material Interaction (PMI) Modeling

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  1. Recent C-MOD, NSTX, and Supercomputing Plasma/Material Interaction (PMI) Modeling J.N. Brooks, J.P. Allain Purdue University PFC Meeting UCLA, August 4-6, 2010

  2. CMOD Mo tile divertor erosion/redeposition analysis[ J.N. Brooks, J.P. Allain, Whyte, R. Ochoukov, B. Lipshultz, PSI-19, J. Nuc. Mat. to be published ] • Puzzling results for Mo tile erosion--high net sputtering erosion in apparent contradiction of some models. • REDEP code package (rigorous) analysis of outer divertor conducted. • Sheath BPH-3D code applied to very near tangential (~0.6°) magnetic field geometry. • D, B, Mo on Mo, sputtering erosion/transport analyzed, 1200 sec. campaign; for 600, 800, 1000, 1100 KA shots, and for OH and RF phases. • Uses TRIM-SP sputter yield and velocity distribution simulations. • RF induced sheath effect studied. W.R. Wampler et al. J. Nuc.Mat. 266-269(1999)217.

  3. C-MOD REDEP/WBC Analysis-Outer Divertor Predicted vs. measured gross erosion over campaign • code/data comparison is OK; agreement within factor of ~2

  4. C-MOD REDEP/WBC Analysis Predicted vs. measured net erosion over campaign. • code/data comparison is poor; ~ 10 X higher net erosion than predicted

  5. Why C-MOD net-erosion code/data mismatch? • Wrong background plasma data? (But why is gross erosion rate comparison OK?) • Missing/incorrect sputtered impurity particle transport physics? (But, this would affect our entire understanding of plasma edge flow) • Data problem? • Could high heat deposition have led to enhanced erosion of the outer strike point diagnostic tiles thin-film marker coatings (300-600 nm Mo on 100 nm Cr). • It is well known that thin-films are highly susceptible to thermo- mechanical stresses, in this case possibly leading to partial Mo layer peel-off (generally more likely than full film loss). This can depend on film conformality, density, adhesion, and surface- roughness. • Obviously, such higher erosion could account for the code/data discrepancy, but evidence (e.g., surface ultrastructure data) is lacking one way or the other.

  6. Future Work C-MOD • Erosion/redeposition analysis of molybdenum outer divertor; code/data comparison for future shots with advanced diagnostics. • Analysis of outer divertor tungsten test-tile experiments.

  7. NSTX is considering replacing (or coating) Horizontal Inboard Divertor (HIBD) carbon tiles with molybdenum.---To reduce carbon sputtering & core plasma carbon content. • Our analysis goal: Determine if Mo sputtering and plasma contamination is acceptable. REDEP/WBC NSTX Inner Divertor Analysis; with Molybdenum surface [with PPPL, ORNL ]

  8. REDEP/WBC NSTX Mo Analysis

  9. NSTX Inner Divertor Plasma Solution (J. Canik SOLPS code) Peak plasma values (near inner separatrix) Ne ~ 1x1020 m-3 Te ~ 60 eV

  10. REDEP/WBC code package--computation of sputtered particle transport 3-D, fully kinetic, Monte Carlo, treats multiple (~100) processes: • Sputtering of plasma facing surface from D-T, He, self-sputtering, etc. • Atom launched with given energy, azimuthal angle, elevation angle • Elastic collisions between atom and near-surface plasma • Electron impact ionization of atom→impurity ion • Ionization of impurity ion to higher charge states • Charge-exchange of ion with D0 etc. • Recombination (usually low) • q(E +VxB) Lorentz force motion of impurity ion • Ion collisions with plasma • Anomalous diffusion (e.g., Bohm) • Convective force motion of ion • Transport of atom/ion to core plasma, and/or to surfaces • Upon hitting surface: redeposited ion can stick, reflect, or self-sputter • Tritium co-deposition at surface, with redeposited material • Chemical sputtering of carbon; atomic & hydrocarbon A&M processes • Mixed material characteristics/evolution

  11. NSTX Molybdenum Inner Divertor: WBC Results

  12. WBC NSTX Inner Divertor Molybdenum analysis: transport summary (100,000 sputtered histories/simulation) PRELIMINARY ANALYSIS (no C or LI sputtering, prelim. sheath & near-surface plasma models) a for Mo atom ionization, normal to surface b from ionization to redeposition c average, for redeposited Mo ions, over 30 cm wide inner divertor surface

  13. Future Work-NSTX • BPHI-3D code analysis of inner divertor sheath (w/ G. Miloshevsky Purdue) • WBC analysis of inner Mo divertor, with C, Li sputtering, rigorous sheath solution, non-preliminary misc. models • Inner Mo divertor analysis, with low-recycle plasma solution (UEDGE) • Inner lithium coating divertor analysis • Continuing analysis of (outer) Liquid Lithium Divertor (LLD)

  14. PMI Supercomputing • Fusion Simulation Project (FSP) • Management/planning underway; FSP implementation to start in FY12 (One use for FSP is to explain/predict full ITER shots) • Plasma/material interactions for Plasma Facing Components will be a major planned upgrade • Purdue/LLNL/ORNL FSP proto-effort • Coupled plasma edge/SOL, material response, impurity transport codes on parallel machine(Tatyana Sizyuk-computer implementation, Brooks, Rognlien, Allain, Krstic -science codes) • Coupled, experimentally validated, Material-Response codes (Li/C/O/D analysis) (Allain, Krstic, et al.). • Coupled UEDGE/WBC plasma/erosion-redeposition codes (Rognlien, Brooks) {Planned}

  15. Molecular dynamics simulations involving Li, C, O, H GOAL: development of potentials, validated by Purdue experiments (sputtering, reflection, adsorption, retention) to establish atomistic PMI modeling of the Li-C-O-H system TEAM:JP Allain (Purdue Univ, experiments) with E. Yang(Purdue student, modeling and exps) major effort led by ORNL (P. Krstic, P. Kent, J. Dadras), A. Allouche (CNRS*) Electronegativities: (according to Pauling definition). Li : 0.98 C : 2.55 O : 3.44 H : 2.20 New, long range term, requires charges recalculations at each MD step, by Electronegativity Equalization Method (EEM) QM methods used: CCSD(T), MP2, DFT(PW) :GGA, hybrids (B3LYP...), meta-GGA ... • Li-alone (bound to itself): similar to any other metal: Metallic bonding, well parameterized Tersoff-Brenner bond order potential sufficient • Problems when Li mixes with C, H, O: Li much different electronegativity than others charges positive, polarizing the medium: ionic metal 15 *Centre National de la Recherche Scientifique

  16. CMOD Molybdenum divertor Analysis • Analysis completed for complex, ~1200 sec campaign, with 8 plasma conditions. • Acceptable code/data comparison for gross Mo erosion, not good for net erosion-puzzling result. • RF sheath significant but not a major effect. • Work continues • NSTX Inner Divertor Analysis; with Mo surface • Preliminary results : • -- encouraging: Mo sputtering is low; no core plasma contamination problem • -- cautionary: Self-sputtering high near strike point • Full analysis needed and is being done • PMI Supercomputing • Plasma/material interaction modeling for PFC’s planned for Fusion Simulation Project Conclusions

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