Modeling Carbon Diffusion in W-Armor Shahram Sharafat and Nasr Ghoniem Graduate Students: Jaafar El-Awady Michael Andersen Qyiang Hu Jennifer Quan Andrew Chen Wen Guo (Alice Ying) University of California Los Angeles, CA. The High Average Power Laser (HAPL) Program Workshop Rochester, New York November 8 and 9, 2005
OUTLINE Brief Summary of UCLA Activities: Ion Implantation: Roughening Modeling Interface Bond Strength Measurements Ion Implantation: Carbon Implantation Profile Multi-physics Simulation Buildup ?
Modeling Surface Roughening POSTER Grooving patterns can appear in long rows, but crosshatch ends the valleys from continuing indefinitely. TOOLS: (1) Sharp Interface Approach (2) Phase-Field Modeling: Solution is a summation of free energies from elastic (fe), gravity (fgravity), double well potential (fdw), and an equilibrium control (fc). L.O. Eastgate Phys.Rev.E,65 Simulated phase field solution of a crack. Michael Andersen, (Ph.D. Thesis) Goal: Predict crack formation by modeling surface roughening Surfaces ROUGHEN to alleviate stresses. Solid buildup decreases elastic energy by growing tips (low stress). “Deepening valleys” (material with high elastic energy is removed). Sources of Stress: Thermo-mechanical (Biaxial) J. Blanchard HAPL Nov.’05
Measurement of W - F82H Bond Strength Using Laser Spallation Interferometry POSTER Jaafar El-Awady, Jennifer Qua, et. al. Goal: Quantify the Interface bond strength between tungsten and F82H Approach: Laser Spallation interferometry measurements Experiment: ITER (JAERI) HIP’d W/F82H samples were tested. Used 6 different laser fluence energies to determine the critical energy. 50 mm W F82H D = 20 mm Laser Fluence: 1065 mJ Interfacial stress history Laser Fluence (mJ): 613 1065 1329 1577 1708 1737 Failure: No Failure Some Cracks generates at the interface Severe interfacial damage Severe interfacial Damage F82H W 100mm Laser Fluence: 1708 mJ Delamination Interface Crack Results Severe interfacial damage occurred above 1577 mJ. Analysis results in a bond strength between 300 and 450 MPa (depending on Young’s Modulus of W; 390 and 195 GPa, respectively)
Ion Implantation: (1) Helium (2) Carbon
Carbon Implantation Profile (SRIM) Threat Spectra (405 MJ): C = 1.07x1019 /shot Peak: ~0.4 um Avg. C/ W Ratio: ~ 2.5x10-7 (apa) Pellet Geometry: CH layer 3 mm r = 2.264 mm C/ W~4.1x10-7 (apa) DT gas DT fuel 1 .734mm 2.264mm DT ablator (+ low density CH foam) 2.059mm 3mm solid CH shell 148mm empty foam 100mg/cc 2.415mm (Perkins, HAPL Oct’04)
C-Buildup: No Carbon Diffusion (SRIM 2003) HAPL June ’05 154 MJ Target
Carbon Diffusion Model Multi-physics problem Consider Carbon Diffusion with R = 0: No WC or W2C Future work will consider carbide formation (R ≠ 0) Carbon Diffusion in Tungsten ? http://FusionNET.seas.ucla.edu (Eckstein, 1999) (Eckstein, 1999)
Multi-physics Diffusion Solution Used ANSYS to solve the diffusion equation: it worked Needed to couple temperature with diffusion in ANSYS: did not work Briefly considered: Neutron Transport Use COMSOL (PDE Solver) to solve the coupled thermal & diffusion model Temperature: T(x,t) IC: Implantation Profile C(to) Range (um) C / W (apa) ( fit SRIM data )
Carbon Concentration Profiles IC Profile C(to) Range (um) C / W (apa) 14 mm 1 mm
Carbon Concentration Profile
Carbon Concentration Profile
Quasi Steady State Diffusion Approximation Quasi Steady State Parameters: Carbons per shot 1.07 1019 ions Avg. Carbon Flux (r=10.1 m, 10 Hz) 8.35 1016 m-2 s-1 Avg. W-Temperature (50 um) 500 oC Diffusion Pre-exponential (Do) 3.15 107 m2 s-1 Activation Energy (Q) 1.78 eV Quasi Steady State Carbon Concentration: The F82H cooling structure remains protected from Carbon (50 um W-armor) T = 500 oC
Carbon Diffusion: Observations The high W-surface layer temperatures facilitate C diffusion in W. Carbon does not preferentially diffuse out from surface but also spreads inwards (towards F82H). C-to-W ratio of 1 can be reached in <10 days (~2 mm at 10 Hz; r =10.1 m, 405 MJ). Quasi Steady State Analysis shows that F82H steel wall is protected from C pickup (C reaches ~20 um; < 1 year). Formation of W2C and WC was not considered (would slow C-diffusion until C/W ratio > 1). Evaporation of C from WC surface was not considered: It would increase C loss from surface; WCW2C above 2000 oC(1). 1Yamada, JNM 2000
WC-W2C: Thermo-Mechanical Impact * Concerns: Lower KIC , s affects mechanical response (crack nucl. & growth). Lower k, Tm may impacts thermal performance of FW. High C-content might impact Tritium release rates W2C forms at ~800 oC and WC forms(1) at ~1000 oC Helium release from WC above 1200 oC is similar to W(2). 1Hatano 2005; Roth 2001 2 SiC-B4C data: Hino-JNM-1999