Opened 12 months ago

Last modified 12 months ago

#375 reopened physics

collisionsal ionization/3b recombination sink/sources to ground state of isosequences fails to produce LTE at high densities

Reported by: fguzman Owned by: nobody
Priority: major Milestone: C17_branch
Component: etc Version: trunk
Keywords: LTE, ionization Cc:

Description

The sources and sinks due to collisional ionization and three body recombination in the He iso-sequence are wrongly delivered to all excited states through a partition function. The reactions that matter are:

He(nl) + e <-> He+(1s) + 2e

where nl is any resolved state. However cloudy is delivering these populations to:

He(nl) + e -> He+(n'l') + 2e

through the partition function. The inverse reaction is duplicated for every n'l' (no partition function) :

He+(n'l') +2e -> He(nl) + e

The code that allows that possible is:

if (0) {

creation[0] += source; for( level=0; level < numlevels_local; level++ ) {

z[level][level] += sink;

}

} else {

Try Boltzmann weighting to capture LTE limit correctly t_iso_sp* sp = &iso_sp[ipISO][nelem]; double partfun=0.0; for ( level = 0; level < numlevels_local; level++ ) {

partfun += sp->st[level].Boltzmann()*sp->st[level].g();

} source /= partfun; for( level=0; level < numlevels_local; level++ ) {

creation[level] += source*

sp->st[level].Boltzmann()*sp->st[level].g();

z[level][level] += sink;

}

}

If the physics were correct, the first branch of the if clause should be allowed. However the current configuration produces correct LTE limits while the correct physics fails in producing that. This is seen in the wrong departure coefficients of He+ in the tsuite simulation limit_lte_he1_ste.in and in the modified attached sim limit_lte_he1_coll_t50k.in. It is possible that a bug in ionization-recombination balance produces this problem.

Attachments (2)

limit_lte_he1_coll_t50.out (108.9 KB) - added by fguzman 12 months ago.
output of limit_lte_he1_coll_t50
limit_lte_he1_coll_t50_cloff.out (143.6 KB) - added by fguzman 12 months ago.
output of limit_lte_he1_coll_t50 without continuum lowering

Download all attachments as: .zip

Change History (5)

Changed 12 months ago by fguzman

Attachment: limit_lte_he1_coll_t50.out added

output of limit_lte_he1_coll_t50

Changed 12 months ago by fguzman

output of limit_lte_he1_coll_t50 without continuum lowering

comment:1 Changed 12 months ago by fguzman

If continuum lowering is disabled using the "sink/sources to the ground state" configuration, departure coefficients of ground state rise several orders of magnitude as can see in the second attachment limit_lte_he1_coll_t50_cloff.out

comment:2 Changed 12 months ago by rjrw

Resolution: invalid
Status: newclosed

If you want to put the ionization only into the ground state, to maintain LTE you'd have to recombine only from the ground state, rather than all levels.

Assuming the 3-body recombination rate is independent of excitation seems a more reasonable estimate than taking the recombination rate from excited states to be zero. Thermodynamic consistency then requires partition function weighting of the collisional ionization rate source. You don't need partition function weighting on the recomination (sink) side, because you're solving for the populations, though it will appear (as it should) where the recombinations are added as a source to the populations of the lower ion.

comment:3 Changed 12 months ago by rjrw

Resolution: invalid
Status: closedreopened
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