[FLASH-USERS] confusion regarding abar and zbar

[Jonathan Slavin]

Hi all,

I'm doing simulations aimed at understanding aspects of supernova remnant
evolution.  Since the SNR is expanding the general interstellar medium, the
proper mean mass per atom (i.e. neutrals and ions) is about 1.28 amu, given
90% H and 10% He by number.  As I understand it, this is set by the runtime
parameter eos_singleSpeciesA, which corresponds to abar.  If I want to
assume constant, uniform, complete ionization then, as I understand it, I
need to set zbar via the runtime parameter eos_singleSpeciesZ, to a value
of ~1.091 = 1.2/1.1 = (n(H+) + 2*n(He++))/(n(H) + n(He)).  At least that's
what I thought from the docs where at one point it's stated that n(e) =
zbar*n(ion).  However, when I look at density*temperature/pressure*kB/amu,
I get abar.  So it seems that zbar is not used.  What I expect is that
P = (1 + zbar)/abar*kB*density*temperature
Where P is the total pressure (electron pressure + atom pressure).  Is this
not true?  Do I need to specify some extra unit for zbar to be used (maybe
-with-unit=physics/Eos/EosMain/Gamma)?  Am I misunderstanding the meaning
of zbar?  Any help would be appreciated.

Thanks,
Jon

-- 
________________________________________________________
Jonathan D. Slavin                 Harvard-Smithsonian CfA
jslavin at cfa.harvard.edu       60 Garden Street, MS 83
phone: (617) 496-7981       Cambridge, MA 02138-1516
cell: (781) 363-0035             USA
________________________________________________________
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