How to convert 2D weights to equivalent values in 3D

[ouyangchen666]

Dear teacher
For the axially symmetric simulation, how is the weight converted between 2D and 3D?
Assuming in input.deck the parameter is ：
ny = 200, ymin = -20 * micron,
ymax = 20 * micron.
the random fraction of the species is set 1 in the subset block.
I have another question that the weight of a particle with a specific ID will not change at different times, right?

[Status-Mirror]

Hi @ouyangchen666,

There is a basic procedure for this.

In a 2D simulation, the cells are assumed to be 1m in the $z$ direction, which is used when injecting laser energy and calculating macro-particle weights. This will likely be unphysical, as laser spot-sizes are typically on the order of microns, not metres.

Firstly, calculate the laser energy injected into your 2D simulation $L_2$ (you can use the absorption key in the output block). Next, calculate the true 3D laser energy $L_3$ in your system, based on your spatial profile, temporal profile and intensity:

$L_3 = 2\pi\int I(r,t)dr dt$

where $I$ is the cycle-averaged laser intensity at radial position $r$, and time $t$, at some point along the laser path (you can choose focal spot) - the integral is performed over all space and time. Only you know what this is for your laser.

Your simulation injects too much energy by a factor $f = L_2 / L_3$. If you assume the same laser-to-particle-energy conversion efficiency, and assume the same energy-spectrum shape for 2D and 3D simulations, then you need to reduce the 2D macro-particle weights by $f$. This ensures the ratio of the summed particle energy to the 3D laser energy is the same as your 2D simulation.

Hope this helps,
Stuart

[ouyangchen666]

Can 1D simulation use the factor f to convert the weight？
it seens that some problems hanppened in the simulation, the laser absorption varies at different times and can sometimes be negative, which is bad for the factor f calculatoring the total photon number or others.