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

[Galtier, Eric Christophe]

Hi everybody!

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. It only happens at the interface between the target and vacuum. Do you think this oscillating behavior arrises because of the use of a eos_gam for the vacuum side and a eos_tab for the target side? Is there a known strategy to dampen these oscillations and prevent gamc to become negative?

Thanks a lot for your help!

Eric

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