[FLASH-USERS] Expansion of Target

[Lu, Yingchao]

Hi Benbayer,

Is this a 2D cylindrical run? If so, the incident laser should be a ring or cone because of the rotational symmetry. If this is 2D cartesian, then the beam should be an infinite column. Besides the suggestion by others, I also suggest double check the boundary conditions. For example, the laser should not come in from a reflecting boundary. If you use 2D cylindrical, then r=0 should not be open or outflow boundary.

Best,
Yingchao


From: flash-users <flash-users-bounces at flash.rochester.edu> on behalf of "Marissa B. P. Adams" <madams at pas.rochester.edu>
Date: Wednesday, February 16, 2022 at 2:49 PM
To: Andy Sha Liao <andy at f.energy>, "benbayer.kouider at gmail.com" <benbayer.kouider at gmail.com>
Cc: "flash-users at flash.rochester.edu" <flash-users at flash.rochester.edu>
Subject: Re: [FLASH-USERS] Expansion of Target

It looks to me to be a result of too much numerical diffusion. What CFL is being used? What order? Solver? Send your flash.par Benbayer when you get the chance.

I am also curious if the expansion looks the same if you multiply it only by the target species mass fraction for the same pseudo-color scale of density (same min/max).

Best,
Marissa

On Wed, Feb 16, 2022 at 2:41 PM Andy Sha Liao <andy at f.energy> wrote:
Scott,


The target is not expanding nearly as much on the rear side as it is on the front. If the problem is as you described, then the target should expand from both vacuum interfaces, but only the irradiated side is affected.


Andy

On Tue, Feb 15, 2022 at 2:33 PM Scott Feister <sfeister at gmail.com<mailto:sfeister at gmail.com>> wrote:
Hi Benbayer,

This is a well-known issue in our community, for those studying laser-plasma interactions. FLASH treats everything as a plasma. There are no chemical bonds (e.g. solids physics, liquids physics) which are in the code and would physically prevent such expansion. One workaround can be explained better by others, is to "freeze" the hydrodynamics on cells who do not exceed a certain temperature. We can do that using a variable in flash called "BDRY". I will leave it to others to elaborate.

As a starting point, search through our past forum discussions for "BDRY". For example, here's a good syntax in Google to search the entire FLASH website:
"BDRY site:https://flash.rochester.edu/"

https://www.google.com/search?q=BDRY+site%3Ahttps%3A%2F%2Fflash.rochester.edu%2F&oq=BDRY+site%3Ahttps%3A%2F%2Fflash.rochester.edu%2F&aqs=chrome..69i57.4755j0j4&sourceid=chrome&ie=UTF-8

Hope this helps!

-Scott

On Tue, Feb 15, 2022 at 4:14 AM kouider benbayer <benbayer.kouider at gmail.com<mailto:benbayer.kouider at gmail.com>> wrote:
Hi all.
I have observed a problem of expansion of the whole target  over time instead of expansion at the point where the laser is focused.
I am attaching the pseudo plot of density which shows the expansion of the target.
Can anyone have a solution to this issue?
Best regards.
Benbayer.
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