[FLASH-USERS] IONMIX format and HEDP module

[Roman Yurchak]

Hi Eric,

On 18/04/15 16:09, Galtier, Eric Christophe wrote:
> I’m trying to simulated the interaction of a high power laser with solid
> samples. While the HEDP module is fairly straightforward to use, I get
> stuck when I need to use realistic equation of states and opacities,
> meaning tabulated, in the IONMIX format. I basically have SESAME eos
> tables that I want to couple to TOPS multigroup opacity tables. I was
> wondering if any body have exprience to merge SESAME eos tables with
> TOPS opacity tables into IONMIX format? Or more generally, is there some
> python code I could use to convert the SESAME format and/or TOPS format
> into one single IONMIX format containing both the eos and opacity tables?

There is the opacplot2 python module
(https://github.com/icksa/opacplot2) developed by Milad Fatenejad that
can be used for file conversion between different formats, including
SESAME, TOPS and IONMIX.  It's probably easier to create two separate
IONMIX files, one with multigroup opacities, and one with EoS +
ionization (the ρ-T grids don't have to be the same).

# Multigroup opacity tables

This should be rather straightforward, an idea of the fields that would
need to be written to the IONMIX file can be found here
https://gist.github.com/rth/83a52122426611b0a2d6

# EoS tables

An example of a script to convert SESAME (ascii) files to IONMIX can be
found at,
 https://github.com/rth/opacplot2/blob/master/generate_ses/generate_ses2.py
(you would need to use a slightly modified version of
https://github.com/rth/opacplot2/ to run it).

There are several challenges, when using SESAME files in FLASH,
   - SESAME don't always have the same ρ-T grid for the electron and ion
tables: the script above normally handles that
   - we need to write the ionization table on the same ρ-T grid as EoS
data. In the script above, I'm using the basic Thomas-Fermi model. If
you have some better ionization data (from atomic physics codes etc),
you would need to calculate/interpolate it on the same grid.
   - Only equilibrium SESAME tables  can be used (i.e. with Maxwell
constructions) as to avoid negative pressures. And even then, in my
experience low temperature EoS data was a problem for the hydrodynamic
solver, so I have been forced to remove the region below 0.5 eV or so,
depending on the material. I don't know if there are better ways of
handling it.

This is for the the SESAME files in the ascii format. If you have access
to the binary SESAME files, you could try to extract the data with
https://github.com/luli/pyeospac, and then write it to IONMIX with
opacplot2. This is somewhat more complex but would allow to,
   (a) potentially apply Maxwell constructions on the non equilibrium
tables when needed (not tested)
   (b) automatically check that the tables we are writing are
thermodynamically consistent and suitable for use in FLASH: i.e. no
negative pressures, and game, gamc that make sens (no imaginary sound
speeds etc.).
   (c) optionally be able to use the FEOS code (upgrade of QEOS) as an
alternative to SESAME with the same work-flow (allows to create tables
of material mixtures among other things)

> [..] Everythign looks normal except that at some point, a
> schock wave starts to develop in this ambient atmosphere as is shown by
> the huge increase in temperature and density ahead of the plasma plume.
> This shock wave seems to be related to the physical constraint of having
> an atmosphere of whatever low pressure material simulating the vacuum.
> Does anybody already observed this effect in this kind of simulation and
> if yes found a work arround or a way to get rid of this Sedovesque type
> shock wave with this code? 

There are two things I have attempted in similar setups to mitigate this,
  * use a quasi isothermal ideal gas EoS (with say gamma = 1.1) for the
pseudo-vacuum.
  * force de-refinement of the AMR grid in the regions where mass
fraction of the pseudo-vacuum is higher then some threshold value (e.g.
0.5), assuming this is not the region we are interested in. In my runs,
this shock in the pseudo-vacuum was the highest temperature region of
the simulation during laser deposition, and forcing a larger cell size
there therefore lead to a larger global time step through the CLF condition.

Hope this helps,

Best,

Roman
-- 
✐ Roman Yurchak
PhD student
Laboratoire LULI
École Polytechnique
☎ +33 1 69 33 54 13