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

J.N Brooks, PFC/UCLA 8/10 2 CMOD Mo tile divertor erosion/redeposition analysis 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 (1999)217.

J.N Brooks, PFC/UCLA 8/10 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

J.N Brooks, PFC/UCLA 8/10 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

J.N Brooks, PFC/UCLA 8/10 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 ( 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.

J.N Brooks, PFC/UCLA 8/10 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.

J.N Brooks, PFC/UCLA 8/10 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 ]

J.N Brooks, PFC/UCLA 8/10 8 REDEP/WBC NSTX Mo Analysis

J.N Brooks, PFC/UCLA 8/10 9 NSTX Inner Divertor Plasma Solution (J. Canik SOLPS code) Peak plasma values (near inner separatrix) Ne ~ 1x10 20 m -3 Te ~ 60 eV

J.N Brooks, PFC/UCLA 8/ 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 D 0 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 REDEP/WBC code package--computation of sputtered particle transport

J.N Brooks, PFC/UCLA 8/10 11 NSTX Molybdenum Inner Divertor: WBC Results

J.N Brooks, PFC/UCLA 8/10 12 ParameterReference sheath model (Debye-only) Alternative sheath model (Magnetic+Debye) Mean free path a, mm Charge state c Energy c, eV (standard deviation. eV) 491 (303) 213 (212) D + sputtering fraction Self-sputtering fraction Sputtered Mo current/incident D + current 9.6x x10 -4 Sputtered Mo to core plasma-0- Peak gross erosion rate, nm/s Peak net erosion rate, nm/s 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 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)

J.N Brooks, PFC/UCLA 8/10 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)

J.N Brooks, PFC/UCLA 8/10 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 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 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*) New, long range term, requires charges recalculations at each MD step, by Electronegativity Equalization Method (EEM) Electronegativities: (according to Pauling definition). Li : 0.98 C : 2.55 O : 3.44 H : 2.20 QM methods used: CCSD(T), MP2, DFT(PW) :GGA, hybrids (B3LYP...), meta- GGA... *Centre National de la Recherche Scientifique

J.N Brooks, PFC/UCLA 8/10 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