[FLASH-USERS] Optically thin regions in the laser slab example

[Hansen, Eddie]

You would still want radiation transport on in an optically thin region because you want radiation to pass through easily. Turning off transport would make the region optically thick.

If it is truly optically thin, then the transport will help radiation move through it and it will not be absorbed. Any emission that comes as a source from the optically thin region will also escape.

—
Eddie Hansen
Applications Group Leader
Flash Center for Computational Science

On Apr 3, 2026, at 12:16 PM, Chesler, Paul - 0991 - MITLL <Paul.Chesler at ll.mit.edu> wrote:

Dear FLASH users,

I am working through the laser slab example and have a question.  Depending on plasma composition, for some frequency groups the system can be optically thin while for other frequency groups it could be optically thick.  For the optically thick groups, FLASH handles radiation transport via a diffusion solver.  However, for the case of optically thin regions, I would think one would want to include energy loss from radiation emission alone, but not include radiation transport (simply because that emitted radiation does not interact with the plasma).  Does anybody know if there a way one can ‘turn off’ radiation transport for some frequency groups while still taking into account energy losses from emission?

Thanks,
Paul Chesler
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