[FLASH-USERS] Magnetic pressure in USM

[dongwook at flash.uchicago.edu]

Dear Seyit,

Yes, you are correct about the B-field initialization when you choose to use

   unitSystem = "none"

in flash.par for B-fields. "none" is default in FLASH, so unless specified
otherwise, it will be automatically be selected.

Also, note for example that if you initialize Bx=B_flash.par, By=Bz=0,
then the unit of your initial strength of B (or magnetic pressure) is
sqrt(4pi)*(B_flash.par)^2/2 in gauss.

The same goes for all your FLASH outputs, that is, your initial strength
in guass is sqrt(4pi)*B_checkpoint.

If you want to get yourself familiarized with unit systems (cgs, SI, none,
gauss) in electrodynamics, please let me know. I can send you a short note
on them.

Hope this helps!

Best,
Dongwook

=========================================
Dongwook Lee, Ph.D., Research Scientist
FLASH Center for Computational Science
University of Chicago
5747 S. Ellis Ave., Room 319
(773) 834-6830

> Dear users, supporters,
>
> I was wondering how the magnetic pressure is calculated with the
> FLASH4-a USM scheme. Normally, P_mag (=magp) = B^2 / 8 pi. However, it
> seems from the FLASH user's guide, as well as from my preliminary
> results, that the returned magnetic pressure is calculated as B^2 / 2
> (non-dimensional form). If so, this messes with my beta parameter, which
> is P_thermal / P_magnetic.
>
> In order to correct for this, I was thinking of changing my initialized
> B value, such that B* = B/(4pi)^0.5. Am I correct in my reasoning?
>
> Kind regards,
> Seyit
>
>