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Unified Simulation for Thermal Response of Dendrites

Explore updates in UMARCO framework for advanced modeling of thermal processes in dendrites, optimizing material properties and stress distribution. Key focus areas include crack arrays, fracture mechanics, and surface cracking. The framework encompasses a comprehensive approach to simulate ion implantation, stress waves, and thermal stress propagation. Discover insights on dendrite structures, stress management, and sputtering modeling for minimal material loss.

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Unified Simulation for Thermal Response of Dendrites

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  1. Unified MAterialsResponse COde (UMARCO) update& Thermal Response of Dendrites Qiyang Hu (UCLA) Aaron Oyama (UCLA) Shahram Sharafat (UCLA) Jake Blanchard (Wisc) Nasr Ghoniem (UCLA) 19th HAPL Meeting University of Wisconsin, Madison Oct. 22-23, 2008

  2. Unified Simulation • Unified Model would • Avoid inconsistencies • Simplify modeling of wide variety of situations • New tool will model: • Heating profile (x-rays and ions) • Transient temperatures, stresses, strains • Fracture mechanics • Ion deposition profile, diffusion, and clustering

  3. 2 1 UMACRO Fortran’90 C++ HAPL pellet spectrum Material: Mech Prop. Material: SRIM Vol. Heating Rate Ion Implant. Profile Constitutive Lawelastic, plastic Temperature Coupled Diffusion Module:Ion, Helium, Bubbles, Carbon Transient stress strain field Module Stress WavesCoupled Fracture Module Improved

  4. Modeling of Surface Cracking • Stress intensity factor decreases as cracks grow further from surface • Crack growth will arrest • Crack arrest will be more shallow for short pulse experiments (like RHEPP) UW

  5. Crack Arrays • What if we have an array of cracks? • This will tend to relieve the stresses h TOFE 2008

  6. Results for Crack Arrays KIC 7 MPa·m1/2 for recrystal W (A.V. Babak, 1981)

  7. Reproducing HEROS • User defined f(t,y) • f(t,y) = react + diff + drift • reaction + drift term: • 13(18) variables: Alhajji-Sharafat-Ghoniem • 13+2 (temperature & carbon) • Test Results: • Single shot case: • UNC, UWM, ITER: OK! • Diffusion behavior is more obvious. • Multiple shot case: • 2 shots of “const temperature” HAPL case: OK! • Non-const temperature: • Linear from 400 C to 2000 C: OK!

  8. Solving thermal stress wave problem • Thermal wave stress governing equations: • System specifications: Q’’’ Stress-free& adiabatic Stress-free& temperature const. 20 ~ 200 Grids 10 m  3mm

  9. Numerical considerations • 3 ODE equations: • A proper cvode option tested by bubble diffusion: • Solver: Krylov solver SPGMR • Precondition: CVBANDPRE module • Activate stability limit detection • Spatial finite-difference scheme:

  10. Heating Rate (Q’’’) in HAPL • Ion implantation: ~0.1sec per step The most severe case:

  11. Quasi-static Decomposition • Stress wave propagation time: • Thermal diffusion time scale: • Decomposition Fast (high frequency) Slow (quasi-static)

  12. Low Frequency Thermo-elastic Wave

  13. High-Frequency Thermo-elastic Waves forSelected Heating Step (duration 0.11sec)

  14. Stress Magnitudes from Elastic Waves

  15. Roughening or Dendrite • Roughening aims at minimizing energies (surface strain & stress) • Ultimately results in NANO- or MICRO-CASTELLATION • Why not start with a micro-castellated surface, similar to the UW-Madison Coral structure • Or simply start with Dendrites: • No surface stress or strains on dendrite surface

  16. Tungsten Dendrite Structures

  17. Dendrite Thermal Response to HAPL Threat HAPL Threat for 10.5 m radius chamber: Tip Radius: 1.5 mm

  18. Dendrite Thermal Response to HAPL Threat Max Tip Temperature = 3836 °C at 4063 ns (end of shot) D=0 95.71 mm Max Base Temperature = 1308 °C at 120 μs after shot D D=95.71

  19. Effect of Tip Radius on Temperature Transient Profile r=1 mm r=3 mm r=5 mm 95.71 mm

  20. Summary & Conclusions • UMARCO (C++) framework completed • Fatigue of Interface Between W/Fe is a Concern. • Tungsten dendrite structure can be fabricated with various aspect ratios and tip radii • A tip radius of 5 mm will prevent tip melting • Mechanical modeling to be done, however stress and strains should remain fairly low because of dendrite geometry • Sputtering modeling including re-deposition shows minimal overall loss of material (see Tim Knowles’s poster).

  21. Extra Slides

  22. Surface temperature comparison UMARCO

  23. Sputtering & RedepositionFor Dense Needle Configuration • Carbon velvet carpets have been used in space applications for ion thruster wall, with encouraging sputtering results after years of operation • Sputtering plus Redeposition modeling shows little loss of geometry (see next viewgraph).

  24. From Tim Knowles Poster

  25. Using CVODE SUite of Nonlinear and DIfferential/Algebraic equation Solversby Alan C. Hindmarsh and Radu Serban Direct: Krylov: Scaled Preconditioned Generalized Minimal Residual method

  26. Crack Depth Measurements in RHEPP

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