[Mesa-users] problems with trace elements diffusion

Mon Mar 21 18:40:43 UTC 2022

Hi Evan, Hi Frank,
sorry it took me so long to get back to you!

*Regarding Evan's questions:*

 We were looking at the abundance profile to monitor diffusion, so by
"diffusion isn't happening" I meant  "the abundance profile is a flat
horizontal line". By adding edv and diffusion_D to the profile_columns
list, MESA reports that for both the uranium isotopes, the diffusion
velocity is *not *zero. I'm attaching one of the final profile.data files
for further detail.

*On Franks suggestions:*
Increasing the mass fraction for both the isotopes does not cause diffusion
to happen.

Now, for the "adding Ne22" suggestions things get a little weird.
When adding Ne22 to the models, diffusion happens not only for the Ne22 but
also for U238 (U235 doesn't diffuse though). The range of diffusion
velocities for U238 and U235 remains pretty similar to the case with no
Ne22. I'm also attaching one of the final profile.data for the case with
Ne22

Also, we accidentally discovered that if Ne22 is present in the add_isos
list U238 will diffuse (even if de initial abundance of Ne22 is zero and it
isn't produced in any of our reactions).

Once again, any insights on what might be happening and why adding Ne22
helps with U238 diffusion (but not U235) would be deeply appreciated.

Kind Regards,
Ana Antonini

Evan Bauer <evan.bauer.astro at gmail.com> escreveu no dia segunda, 21/02/2022
à(s) 18:31:

> Hi Ana,
>
> Just to follow up on Frank’s question, what exactly does it mean that
> diffusion is not happening? Is the diffusion velocity reported by MESA
> exactly 0? I.e. what gets reported in your profile output if you add the
> following to your profile_columns.list file?
>
> edv u238
> diffusion_D u238
>
> I think MESA should be able to do diffusion in this regime, but the
> diffusion velocity for an element with such a high charge might be very
> slow, so it will be helpful to know the exact numbers that MESA is
> reporting.
>
> Cheers,
> Evan
>
> On Feb 19, 2022, at 8:29 AM, Ana Antonini via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
>
> Hi Frank,
>
> That's not something we've thought of trying before, so I'll have to
> test it out and get back to you.
> But regarding the last question, yeah, models are running long enough.
>
>  Thanks for the suggestions!
>
> A. Antonini
>
> Francis Timmes <fxt44 at mac.com> escreveu no dia quinta, 17/02/2022 à(s)
> 22:25:
>
>> hi ana,
>>
>> some suggestions sparked by this one:
>>
>> > Diffusion is definitely happening, just not for the uranium.
>>
>> if ne22 is added to the composition in the file "u238",
>> then neon diffuses as expected but uranium does not?
>>
>> does increasing the uranium mass fractions in the file "u238"
>> by a factor of, say, 1e6 cause uranium to diffuse as expected?
>>
>> are the models being run long enough relative to uranium's diffusion
>> timescale?
>>
>> fxt
>>
>>
>>
>>
>>
>>
>>
>> > On Feb 17, 2022, at 11:58 AM, Ana Antonini via Mesa-users <
>> mesa-users at lists.mesastar.org> wrote:
>> >
>> > Hi Morgan,
>> >
>> > we set "do_element_diffusion" to true on our run_star_extras file so
>> that it only starts once the star is in the wd cooling track.
>> > Diffusion is definitely happening, just not for the uranium.
>> >
>> > thanks for taking the time to try to help though!
>> >
>> > Morgan Taylor <taylormorgan32 at gmail.com> escreveu no dia quinta,
>> 17/02/2022 à(s) 15:23:
>> > Hi Ana,
>> >
>> > I noticed that !do_element_diffusion =.true. is commented out in your
>> inlist.
>> > In r-15140, the default is set to false.  Does your inlist_extra file
>> set it to true?
>> > If not, diffusion won't be turned on, and your other diffusion controls
>> will be ignored.
>> >
>> > Hope this helps,
>> >
>> > Morgan
>> >
>> > On Thu, Feb 17, 2022 at 10:53 AM Ana Antonini via Mesa-users <
>> mesa-users at lists.mesastar.org> wrote:
>> >
>> > Dear Mesa users,
>> >
>> > We've been working on a project using MESA version r-15140 and have run
>> into a problem we can't seem to solve.
>> >
>> > We've been trying to investigate if the results from Horowitz & Caplan
>> (2021) can be reproduced with stellar evolution models, but despite trying
>> a broad combination of controls and parameters, we can't get our uranium
>> isotopes to actually diffuse.
>> > Some of the things we tried:
>> >       •  setting a more rigorous tolerance for "diffusion_X_tot_atol"
>> and "diffusion_X_tot_rtol"
>> >       • forcing diffusion by setting "diffusion_class_factor" higher
>> for the uranium species
>> >       • limiting the timestep by using "diffusion_dt_div_timescale"
>> >       • adding the timestep controls used in the wd_diffusion
>> test_suite to our work
>> >       • both using and not using the full net
>> >       • setting the class_factor to zero for all classes except
>> uranium
>> > I'm attaching our inlist as well as other pertinent files and would
>> greatly appreciate any ideas you might offer or even just a confirmation
>> that  MESA is indeed capable of doing diffusion for species with such a low
>> abundance.
>> >
>> > Kind  Regards,
>> > A. Antonini
>> > _______________________________________________
>> > mesa-users at lists.mesastar.org
>> > https://lists.mesastar.org/mailman/listinfo/mesa-users
>> >
>> > _______________________________________________
>> > mesa-users at lists.mesastar.org
>> > https://lists.mesastar.org/mailman/listinfo/mesa-users
>> >
>>
>> _______________________________________________
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