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

[Klaus Weide]

On Sat, 23 May 2020, Galtier, Eric Christophe wrote:

> ... 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? 

I don't think we see strange oscillations (or extreme values) in gamc 
like this when LaserSlab is run with other materials. So the fact alone 
that there is a strong local gradient of pressure (or of anything else) 
does not quite explain it.

I suspect it is most likely that the problem lies primarily with the 
tabulated EOS. Bu I am just guessing.

> 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? 

Of course there are Hydro parameters that you could vary, starting with 
the CFL factor.

I also wonder whether you see other quantities going to unphysical values 
when (or just before) gamc goes crazy. For example, very low or high 
pressures or temperatures (either Tele or Tion).

Klaus