[FLASH-USERS] Laser intensity in 2D cartesian LaserSlab

[Wu, Yaoxing]

Hi Kirill,

I am also trying to use the FLASH 4.7 code for a couple of laser produced plasma (LPP) application in 2D LaserSlab simulations in cartesian geometry.

For your first question, the third dimension of the laser spot size should be considered as unit length (1 cm) due to the laser cross-section function type “gaussian1D”. The laser beam intensity in 3D cartesian should be adjusted or set the runtime parameter “ed adjustBeamsTargetIntensity” equal to true in 2D cartesian. I attached this part description from the FLASH 4.7 manual to let you know how to convert the laser intensity. I hope this could help you.

For your second question, I also find some description about the “depo” variable and attached it but I am not sure whether it will help you.

By the way, I also have a question about how to add an external constant magnetic field during the LPP LaserSlab simulation. I would really appreciate it if you could provide some help.

Thanks.

Regards,
Yaoxing Wu

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________________________________
From: flash-users <flash-users-bounces at flash.rochester.edu> on behalf of Kirill Lezhnin <klezhnin at princeton.edu>
Sent: Saturday, April 22, 2023 6:22:57 AM
To: flash-users at flash.rochester.edu <flash-users at flash.rochester.edu>
Subject: [FLASH-USERS] Laser intensity in 2D cartesian LaserSlab

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Hi all,

I am trying to use the FLASH code (in particular, the LaserSlab branch) for a couple of HEDP applications, and I would really appreciate it if you could help me to clarify a couple of things related to laser intensity in 2D LaserSlab simulations in cartesian geometry.

First: when I define laser pulse for the LaserSlab 2D cartesian simulation, I specify its intensity distribution in the simulation plane (by using cross-section function type “gaussian1D"). I wonder how should I interpret the third dimension (i.e., out of the simulation plane) when calculating laser intensity on target from the power value given in the par file? Should I assume that laser intensity has the same distribution as the in-plane one? Or should I treat the third dimension as a uniform slab with the unit thickness (like, 1 cm)? My current comparisons with inverse Bremsstrahlung absorption suggest that it is the latter, but it would be great to double-check it!

Second: to compare my FLASH results to the PIC results with the laser energy deposition module, I’d like to calculate absorbed laser power density (i.e. quantity with the units of erg/s/cm^3). In FLASH, as far as I am aware, there is a ‘depo’ variable, which calculates “amount of laser energy deposited in a cell per unit mass”, i.e. something like erg/g. I am not quite sure how to convert it to the power density I am looking for. My current assumption is that the deposited laser energy in depo variable is stored for the last timestep, and then the absorbed power density = depo*dens / dt. Is my assumption correct?

Thanks!

Sincerely yours,
Kirill Lezhnin
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