[mesa-users] crazy C shell burning

[Bill Paxton]

Hi Tug,

I've finally cleared other tasks enough to run your problem case using my current version (4917),
and it seems that enough has changed in the code that I can't reproduce the crazy behavior for alpha=1.

here's my alpha = 2 plot
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and here's plot I get for alpha = 1
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identical inlists except for mixing_length_alpha.

Could you try this with a more recent version of mesa --- 4906 is the current release.
I hope you understand my reluctance to go chasing bugs in old versions!

Thanks,
Bill

here's the inlist I used.
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On Apr 16, 2013, at 10:24 PM, Tuguldur Sukhbold wrote:

> Dear MESA users,
> 
> many of us are now well aware that due to lack of NSE treatment you're likely to get into trouble during Si burning. But in my 2+ year experience with MESA I have seen many times this weird behavior well before Si ignition, during the C burning. The attached plot shows the central T and rho evolution during C burning for two identical 15Msun models with different alpha_mlt. You see the alpha_mlt=2 case goes smoothly, but the alpha_mlt=1 case is doing some crazy stuff. I could wait for thousands of time steps and it would be just doing its weird loops back and forth, and never manage to ignite Ne.
> 
> With older MESA versions I noticed sometimes even very slight changes in the composition could result into this problem during C burning. If I remember correctly, during the last summer school Josh Shiode also reported similar results when he played with the time step and zoning (?) parameters.
> 
> I was wondering if anybody had looked into details of why this happens? how to avoid? previously I used to almost 'randomly' play with certain parameters until I find that sweet spot to make it through C burning. But now I am trying to make a detailed comparison with another code, so i need to be a bit careful.
> 
> thanks,
> Tuguldur
> 
> ***just to clarify, in this plot the alpha_mlt=1 case only shows data since the ignition of C in the core. While the other case shows data from previous evolution.
> 
> <Screen Shot 2013-04-16 at 9.51.50 PM.png>
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