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
 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
electron heat conduction
Compression work
collisional exchange
radiation/electron
energy 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 update
o 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-KrylovSchwarz 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 physics
o
o
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
o
o
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
o
o
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
o Add Poisson noise due to finite photon count.
o Smooth at the scale that corresponds to the pinhole size.
Pure Hydro Results
 3 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 date
o 2 μm spacing
o 2400 x 480 x 480 uniform grid
o 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
Tube
Nozzle
8 μm
4 μm
2 μm
1 μm
Full Physics Results
 2 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 resolutions
o 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-driven
X-Ray case
CRASH-driven
X-Ray case
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)