Simulations of the ExperimentsKen Powell

CRASH ReviewOctober, 2010

CRASH PreprocessorHyades is a Lagrangian rad-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)

CRASH Radhydro Code: Hydro and Electron Physics

radiation/electron momentum exchange

radiation/electron energy exchange

electron heat conduction

Compression work collisional exchange

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 gth group:advection compression work photon energy shift

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 updateo Hydro and electron equations

Advection, compression and pressure force updated explicitly Exchange terms and electron heat conduction treated implicitly

o Radtran Advection of radiation energy, compression work and photon shift are evaluated

explicitly Diffusion and emission-absorption are evaluated implicitly

o Implicit scheme is a block-ILU-preconditioned Newton-Krylov-Schwarz scheme

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

Improvements to fidelity/efficiency finished this year

Electron/radiation physicso Flux limiting added - limit Spitzer-Harm flux by fraction of free-streaming heat fluxo Update based on total energy, but slope limiter applied on primitive variables

EOS and opacity calculationso Five material (Xe, Be, Au, acrylic, polyimide) EOS and opacity tables in placeo EOS tables made reversible (E→p→E or p→E→p puts you back where you

started)

Efficiency improvementso New block-adaptive-tree library (BATL); Efficient dynamic AMR in 1, 2 and 3Do Semi-implicit scheme, split by energy group

Requires less memory and CPU. Allows PCG.

Synthetic radiographs with blurringo Add Poisson noise due to finite photon count.o Smooth at the scale that corresponds to the pinhole size.

Pure Hydro Results3 geometries

o Straight tube (1200 μm diameter)o Step (1200 μm → 600 μm)o Nozzle (1200 μm → 600 μm)

250 μm Be disk, low laser energy

Shock speed ~ 20 km/s

Highest 3D resolution to dateo 2 μm spacingo 2400 x 480 x 480 uniform grido 550 million cells

Pure Hydro Results – Density Contours

Nozzle – Vertical cut

Nozzle – Horizontal cut

Step – Vertical cut

Step – Horizontal cut

Pure Hydro Results – Resolution Effects

1 μm

Tube Nozzle

2 μm

4 μm

8 μm

Full Physics Results2 geometries

o 2D Straight tube (600 μm)o 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 resolutionso 2D - 2 μm effective (1 AMR level)o 2D - 0.5 μm effective (3 AMR levels)o 3D - 4 μm effective (1 AMR level, 5 million cells)

2D Results – Tube @ 2 μm Resolution

2D Results – Tube @ 0.5 μm Resolution

3D Results – Elliptical Nozzle @ 4 μm Resolution

Ongoing Challenge – Morphology Conundrum

The morphology conundrum persists independent of:

Mesh resolution (except on very coarse grids)

Flux function, limiter

Gray vs multigroup/number of groups

Treatment of electron physics

Number of materials used

Presence or absence of a symmetry axis

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…

… and we get different results when initializing the same case using Hyades

Hyades-drivenX-Ray case

CRASH-drivenX-Ray case

The path aheadWe 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)