[FLASH-USERS] Large numerical diffusion between chamber gas and target species in LaserSlab problem

[David Montgomery]

Blake, this is what I sent to the flash users list 
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Dear Flash Users and Developers,

We are running a modification of a 2D cylindrically symmetric laser slab problem. The laser is normal incidence in the positive Z (positive Y in hydro), with a supergaussian intensity profile.

We have created a pre-plasma in the simulation_initBlock.F90 routine to help mitigate laser imprint by initializing the He chamber gas to 10 eV and having a hyperbolic tangent (TANH(x)) smoothing function on the laser-irradiated side with width smaller than the target thickness.

Early enough times in the run do not show any or much mixing between the polystyrene target species and the low density Helium gas species, so we don’t think that’s our problem.

However, as the plasma expansion develops, a Sedov-like blast wave is driven through the Helium chamber gas, getting to very high ion temperatures (40 keV), and we see numerical diffusion between the low-density helium chamber gas and the target (see attached plots). Otherwise the electron temperature and electron density plots look reasonable, especially when compared to 1D Lagrangian simulations without the need for a “chamber gas”.

Is there a way to suppress diffusion between the two species? We think the artificially-high Sedov-like blast wave may be driving diffusion between the two species.


Thanks,

David

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