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Simulations of the Experiments

Simulations of the Experiments. Ken Powell CRASH Review October, 2010. CRASH Preprocessor. Hyades is a Lagrangian rad -hydro code that can model laser-plasma interactions Used in the early stage (first 1.1 ns) of the simulations

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Simulations of the Experiments

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  1. Simulations of the Experiments Ken Powell CRASH Review October, 2010

  2. CRASH Preprocessor • Hyades is a Lagrangianrad-hydro code that can model laser-plasma interactions • Used in the early stage (first 1.1 ns) of the simulations • Map Hyades Lagrangian result to CRASH Eulerian grid, via triangulation and interpolation • Ongoing work to build our own laser package (see Igor Sokolov’s talk) • Have also experimented with X-ray-driven initialization by CRASH or Hyades (See Eric Myra’s and Erica Rutter’s posters)

  3. CRASH Radhydro Code: Hydro and Electron Physics radiation/electron momentum exchange electron heat conduction Compression work radiation/electron energy exchange collisional exchange

  4. CRASH Radhydro Code: Multigroup diffusion • Radiation transport equation reduces to a system of equations for spectral energy density of groups. • Diffusion is flux-limited • For the gthgroup: advection compression work photon energy shift

  5. Overview of Solver Approach • Self-similar block-based adaptive grid • Finite-volume scheme, approximate Riemann solver for flux function, limited linear interpolation • Level-set equations used to evolve material interfaces; each cell treated as single-material cell • Mixed Implicit/Explicit update • Hydro and electron equations • Advection, compression and pressure force updated explicitly • Exchange terms and electron heat conduction treated implicitly • Radtran • Advection of radiation energy, compression work and photon shift are evaluated explicitly • Diffusion and emission-absorption are evaluated implicitly • Implicit scheme is a block-ILU-preconditioned Newton-Krylov-Schwarz scheme

  6. CRASH Postprocessor • Synthetic radiographs generated by integrating absorption coefficients along lines of sight • Poisson noise is added to simulate finite photon count • Smoothing is done at scale associated with finite aperture in experiment • Tests included in verification suite – grid-convergence studies on problems with analytical solutions

  7. Improvements to fidelity/efficiency finished this year • Electron/radiation physics • Flux limiting added - limit Spitzer-Harm flux by fraction of free-streaming heat flux • Update based on total energy, but slope limiter applied on primitive variables • EOS and opacity calculations • Five material (Xe, Be, Au, acrylic, polyimide) EOS and opacity tables in place • EOS tables made reversible (E→p→E or p→E→p puts you back where you started) • Efficiency improvements • New block-adaptive-tree library (BATL); Efficient dynamic AMR in 1, 2 and 3D • Semi-implicit scheme, split by energy group • Requires less memory and CPU. Allows PCG. • Synthetic radiographs with blurring • Add Poisson noise due to finite photon count. • Smooth at the scale that corresponds to the pinhole size.

  8. Pure Hydro Results • 3 geometries • Straight tube (1200 μm diameter) • Step (1200 μm→ 600 μm) • Nozzle (1200 μm→ 600 μm) • 250 μm Be disk, low laser energy • Shock speed ~ 20 km/s • Highest 3D resolution to date • 2 μm spacing • 2400 x 480 x 480 uniform grid • 550 million cells

  9. Pure Hydro Results – Density Contours Nozzle – Vertical cut Nozzle – Horizontal cut Step – Vertical cut Step – Horizontal cut

  10. Pure Hydro Results – Resolution Effects Tube Nozzle 8 μm 4 μm 2 μm 1 μm

  11. Full Physics Results • 2 geometries • 2D Straight tube (600 μm) • 3D Nozzle (1200 μm → 600 μm) • 20 μm Be disk, nominal laser energy (3.8 kJ for 1 ns) • Shock speed ~ 160 km/s • Electron physics, five materials, 30 energy groups • Varying resolutions • 2D - 2 μm effective (1 AMR level) • 2D - 0.5 μm effective (3 AMR levels) • 3D - 4 μm effective (1 AMR level, 5 million cells)

  12. 2D Results – Tube @ 2 μm Resolution

  13. 2D Results – Tube @ 0.5 μm Resolution

  14. 3D Results – Elliptical Nozzle @ 4μm Resolution

  15. Ongoing Challenge – Morphology Conundrum

  16. The morphology conundrum persists independent of: • Mesh resolution (except on very coarse grids) • Flux function, limiter • Gray vsmultigroup/number of groups • Treatment of electron physics • Number of materials used • Presence or absence of a symmetry axis

  17. We CAN make a primary shock with realistic structure with different initial conditions (X-ray-driven) running CRASH alone But it is hard to get the primary shock and the wall ablation to simultaneously match the experimental result…

  18. … and we get different results when initializing the same case using Hyades Hyades-driven X-Ray case CRASH-driven X-Ray case

  19. The path ahead • We are further pursuing the X-ray-driven case, comparing Hyades and CRASH to understand how the differences arise • We are developing a laser package, so we have an alternative preprocessor, one whose internal working we understand/have control over • We are working to improve the preconditioning of the implicit solve, to cut down the compute time (approximately 90% of compute time is spent here)

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