[FLASH-USERS] Persistent gaps in laser rays causing non-uniform heating and undesirable plasma fluctuations

[David Montgomery]

Dear FLASH User community,

FLASH newbie here again. I’m currently modeling a thick CH foil in 2D cylindrical geometry, with the laser beam hitting the slab at normal incidence from below (lens defined at Z= -120 cm traveling in the +Z direction, centered at R=0 (X=0), 2D Gaussian profile. The header in the flash.par file says two beams, but starting simple with a single beam.

Everything in the simulation looks okay and otherwise reasonable (shock strength, pressure, plasma temperatures, etc.) EXCEPT for some undesirable non-uniform laser deposition due to what looks like some persistent gaps in the laser rays, particularly near R=0, and some other radii. The laser deposition doesn’t look very uniform. I am using 3D-in-2D ray tracing (couldn’t get 2D-in-2D to work for this problem, kept giving errors about beam partially outside of domain).

I had tried ed_gridType_1 = “statistical2D” (before I learned to extract the laser rays and visualize them), and I was still gettting similar results, so I went back to the “Radial2D” gridtype for this run, and decided to use more laser rays (which increased the run time by 25%, which was not unreasonable).

I attach the flash.par file, as well as the t=0 laser ray plot, and another at t=0.5-ns (halfway through the laser pulse).

I also show the density map on a log scale to show the density modulations created by the non-uniform laser deposition.

My setup command was:

/Applications/FLASH4.8/bin/setup.py -auto TridentSlab -2d +cylindrical -nxb=16 -nyb=16 +hdf5typeio species=cham,targ +mtmmmt +laser +uhd3t +mgd mgd_meshgroups=6 -parfile=Trident2c.par 

Any help or advice would be greatly appreciated!

Thanks again,
David





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