strange Ey field using Laser module about smilei HOT 16 CLOSED

Hi,

Just an idea that could be tested: could it be caused by the absorbing EM conditions in direction y?

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Hi Mickael, Fred,

Thanks for you response.

I tested two cases: (1) same as the case in the first post but change EM boundary condition in y direction to "periodic"; (2) change EM boundary condition in y to "periodic" and use the trapezoidal profile as time profile with slope1= 1 wave cycle and the plateau spanning the remaining time after slope1.

In case (1), the spectrum of Ey looks similar to that in the first post. So these high frequency component in Ey are probably not due to the absorbing boundary condition in y.

in case (2), still, the spectrum of Ey has a substantial amount of high frequency components, similar to that in the first posts. In fact, I think if the high frequency components of Ey are caused by the sharp cut-off in amplitude, then Ez, By and Bz should have these high frequency components too.

I am still not sure why Ey has so many high frequency components. Let me know how you think.

Best,
Xin

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What is the amplitude of Ey compared to the others?

Do you have plots of Ey similar to those you posted for By and Bz?

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The amplitude of Ey is about 10 times larger than that of Ez. This could be seen in the spectrum of Ey and Ez in the first post.

Here is the field pattern of Ey and Ez.

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Maybe some 2-stream instability from the particles that you put in the box ?

What happens if you have no particles ? Do you still see the high frequencies ?

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Hi all,

Sorry for my silence for some time.

I did a test without particles in the box. The wave propagates as light wave as expected. Ey is correct and I did not see any high frequencies in it.

In my simulation setup, there are only background thermal electrons (Debye length = grid size) and immobile protons. There should be no 2-stream instability. Therefore the strange Ey field here should be caused by the procedure of charge and current deposit.

I only find some benchmark tests for the propagation of a EM wave in vacuum (tst1d_0_em_propagation.py, tst2d_0_em_propagation.py, tst3d_0_em_propagation.py). But there is no benchmark test for the propagation of a EM wave in a magnetized plasma. Could the team test this case as a benchmark? Thanks for your help.

Best regards,
Xin

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Attached is my python script for input.

tst2d_em_propagation_plasma.txt

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Could this be an effect of the 2D geometry ? You are looking at the background noise which is much higher in the X and Y direction (plane of the simulation) than in the Z direction for the electric field (no space charge can build up along Z) and inversely for the magnetic field.

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Thanks! I will test a 3D case soon.

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Hello,

I tested a 1D and 3D case. In 1D, both Ey and Ez behave as expected. In 2D, Ez behaves as expected but Ey has a lot of large amplitude high frequency components. In 3D, both Ey and Ez has a lot of large amplitude high frequency components and behave "strange". Therefore, I agree with you that it is an effect of dimensions. The "strange" Ey in 2D is due to the space charge built up in y direction (Ez is correct in 2D since no space charge is built up in z direction). Both Ey and Ez are "strange" in 3D because space charge can be built up in both y and z directions.

Unfortunately, since my problem eventually requires nonuniform magnetic field configuration, 1D model cannot do this. But thanks for your help.

Another unrelated question, when the particle boundary condition is specified as "none" and the field boundary condition is "silver-muller", are the particles removed from the memory at the boundary?

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Concerning the point on particles boundary conditions : I confirm that if silver-muller is selected for fields then the none will apply a supp conditions on particles.

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Thank you all for the responses. Since 4th order for field solver and current smoothing are not available yet in current release of Smilei, I only tried to increase the number of super-particles per cell to reduce the noise. With 400 particles per cell (512 x 512 grids), Ey is 10 times bigger than Ez. With 22500 particles per cell (simulation box is reduce in the transverse direction to finish it in one hour on 8 nodes (36 cores on each nodes), 512 x 16 grids), Ey is 3 times bigger than Ez. Note that Ey is expected to be approximately equal to Ez. I will probably use other approach to tackle my problem. Thanks for your help.

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Thanks Micka. I upgraded to v3.2 and start to use the 4th order interpolation and current filtering. They help mitigate the noise problem. I also noticed that there is an electric field filter mentioned in the Smilei paper on arxiv submitted to CPC. Does this help mitigate the noise and is it available to use in v3.2?

The noise problem matters in my simulation, since my simulation looks at the phase space dynamics of resonant electrons (which will give rise to some triggered emissions) and the amplitude and phase of the electric field matters in this situation.

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