[FLASH-USERS] Problems Simulating Partially Ionized Plasma with USM

[Patrick Rieser]

Hey all!

So I am using a little bit modified Flash 3.3 to do simulations on 
galaxy cluster for my master thesis. We have got a MHD setup using USM. 
By now there are two species defined, H and He and the calculations are 
done with the assumption of full ionization. So now my part is to extend 
the simulation that a partially ionized gas can be calculated with 
neutral parts H and He, and ionized parts H+, He+ and He++. After each 
time step the ionization of those particles should be recalculated. My 
plan has been to modify the USM solver. I thought of integrating two 
different densities, one for the neutral and one for the ionized 
particles. Then add source terms to the flow vectors of the USM solver. 
To get those source terms I would have to modify EOS equations.

Even though I did quite some reading about multifluid MHD and spend 
quite some time playing with flash and it's source code I can't get my 
head around some thing:

1) I recently stumbled over the Ionization module in flash. But I am not 
quite sure if I can use it to do what I want and would not have to 
modify the EOS and USM modules, but change the setup of our simulation. 
This is because of 2)

2) I read the PhD thesis from Dongwook Lee describing the Unsplit scheme 
for multidimensional MHD and tried to pick apart the USM source code but 
I can't really find out how flash handles (multi) species, density and 
Ionization in the USM solver. Does USM work with the Ionization module? 
If so, can USM handle neutral species and the partially ionized plasma? 
Do I just have to implement the Ionized module in the simulation then?

Thanks a lot in advance,
Patrick

PS: Sorry if some questions seem stupid but learning flash can be really 
overwhelming!
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