[FLASH-USERS] gamc divergence at interface for laser/matter interaction

[Galtier, Eric Christophe]

Dear Klaus,

Thanks a lot for your ideas. I attach two screenshots of the code output while I was trying to extract the info you mentioned. The 2D plot shows the value of gamc as a function of time at two different location. In green, it plots the max value in the entire simulation box and in red it shows the value at the center of the laser interaction with the solid. It shows that the negative gamc value happens within the area of the laser interaction. The second screenshot shows the volumetric display of gamc at some time in the simulation history. The red layer is the one at the surface of the material. I was cutting part of the volume to see the interaction at the laser source and that's why there is a 1/4 of the box missing. What this plot shows is that the large change in gamc is not localized to a cell but extends to the entire surface mapped by the material/vacuum interface. Having this large value of gamc at the interface might not seem completely weird since it is a function of the derivative of the pressure vs density and the interface is essentially a gradient. Does it sound reasonable? It also seems that gamc start to be negative very 'abruptly' and goes from a somewhat normal value to a negative value without much intermediate. The laser has its maximum at 500 ps and the tails of the gaussian pulse shape extends all the way down to t=0ps. At 350 ps, the laser intensity is about 1/10 of the peak intensity so there is already some expansion that happened and there should be no specific discontinuities there. I'll keep trying to link it to a pressure point in the EOS. To answer your point 2, the simulation runs ok with this same material and EOS but when I reduce the resolution going from 2.5 mic per cell to 10 mic. So maybe it is more tight to the hydro scheme I'm using rather than the material? Anyway, I'll try to make an Al EOS and check it out as you suggested.

Thanks a lot for your help and have a good weekend!

Eric

---
Dr. Eric Galtier
Matter in Extreme Conditions
SLAC-LCLS
2575, Sand Hill Road
Menlo Park, 94025, CA, USA
Tel : (650) 926-6227

-----Message d'origine-----
De : <flash-users-bounces at flash.uchicago.edu> au nom de Klaus Weide <klaus at flash.uchicago.edu>
Date : vendredi 15 mai 2020 à 9:21 AM
À : flash-users <flash-users at flash.uchicago.edu>
Objet : Re: [FLASH-USERS] gamc divergence at interface for laser/matter interaction

    On Fri, 15 May 2020, Galtier, Eric Christophe wrote:

    > I'm running a case closely related to the laser slab example of the 
    > manual but modified to the material and laser irradiation conditions I'm 
    > interested in. I use ionmix EOS/opacity tables for the target 
    > material, and an ideal gas gamma law for the vacuum that is in front of 
    > the target. I try to set the density of the chamber material to a small 
    > value to mimic vacuum (say 1e-8 cm^-3 while the target is solid density 
    > copper). The code runs properly, until it computes a negative gamc which 
    > force exit the run. When I plot the gamc value in the grid, I can see 
    > the value oscillating with time and increasing in amplitude along the 
    > entire interface between the target and the 'vacuum' material reaching 
    > up to 11 at the interface inside the target. Because of the oscillation 
    > behavior, it actually reaches almost zero at the interface and on the 
    > vacuum side, where the laser heat the target. And at some point in time 
    > (not even at the maximum of the laser peak intensity) this value becomes 
    > negative and force exit the code.

    Hi Eric,

    1. I am not familiar with this behavior.

    2. It would be interesting to know whether something this also happens for 
    simpler materials, maybe aluminum.

    3. It is possible that the gamc behavior comes from the metal material, 
    rather than the "vacuum" EOS, even if the location appears to be outside 
    of the solid, because of mixed-material cells.

    4. It would be interesting to know where in the code the exit is forced;
    in particular, whether this is perhaps an effect of reconstruction within 
    the Hydro unit rather than of the EOS itself.

    5. I just sent a message to flash-users yesterday on a similar topic, 
    where I referred to this code:

               eosData(gamc+i) = eosData(tempToUse+i)/eosData(dens+i) * &
                                 eosData(dpt+i)**2 /  eosData(det+i) &
                               + eosData(dens+i) * eosData(dpd+i)

    I wonder whether you can trace back the extreme gamc values you are 
    getting to this calculation, and eventually to a specific location in your 
    Eos table.


    Klaus

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