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

[Tomasz Plewa]

Dear David -

You may want to consider using the Consistent Multi-fluid Advection 
(CMA) method. It is currently only partially implemented in FLASH to 
ensure species mass conservation, but the full algorithm includes a 
mechanism that limits numerical species diffusion.

The reference work is

    https://ui.adsabs.harvard.edu/abs/1999A%26A...342..179P/abstract

Hope this helps -

Tomek
--
On 7/22/25 14:34, David Montgomery wrote:
> Blake, this is what I sent to the flash users list
> *********
> 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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