[Mesa-users] problems with trace elements diffusion

[Evan Bauer]

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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 
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