[FLASH-USERS] Problems Calculating B-Fields in Partially Ionized Plasma with USM

[Patrick Rieser]

So I am still trying to simulate a optical thin plasma where neutrals 
and ions exist. The Ionization module seems to work (though there are 
some problems / questions left) but I am not quite sure about the MHD 
solver, if the B-fields are calculated right!

Klaus Weide wrote:
> Note that when you have species defined, the Hydro and MHD solvers should
> in effect already integrate several densities, without any further effort:
> namely, partial densities for the various species as well as the usual
> total density.  (This is basically done by advecting the mass fractions.)
>

Are you sure about that? Because when I look at the USM solver, there 
seems to be only one density. I mean it does the Advection of the mass 
fractions, but when solving the MHD equations it only seems to use the 
total density. So it seems to calculate the B-Fields from the total 
density (including neutrals), total energy etc, which I think yields 
wrong fields!

I talked to a theoretical plasma physicist yesterday and he told me that 
in principle one has to solve the MHD equations for the ionized 
particles and the neutral particles (including source terms for 
ionization!) together. One could, if the solver is explicit (is it?), 
first calculate the ionization, then use the MHD solver on the ionized 
particles and finally use a modified MHD solver in the same time step 
(without all the magnetic parts) on the neutral particles. And repeat 
this every step. But this would mean, one would have to introduce 
different densities, energies etc. for the ionized and neutral particles 
and modify every place where a call to those is made. And as far as I 
see this would be an enormous task (even more for a master thesis).

Does anybody have suggestions about how to solve this problem, i.e. how 
to get the correct B-fields?

Thanks a lot in advance!

Best wishes,
Patrick Rieser