Questions About Setting Up a Plasma Sheath Simulation

[AGreatDayForReal]

Hi,I'm new in pic and warpx.I want to run some simulations of plasma sheath, based on Chapter 1, Section 1.2 of Principles of Plasma Discharges and Materials Processing by Michael A. Lieberman and Allan J. Lichtenberg.In the sheaths part, they sets up 4000 electrons as movable particles, with the left wall grounded and the right side suspended by potential, and positive ions as background particles.The electron and ion densities are both 10¹³ m³.The final result should look like the image below.

I have some problems below

1. In the article, it says, "The potential at the right wall is also low, but it oscillates in time." I found that the boundary conditions in WarpX seem unable to simulate the potential changes caused by particle absorption or the charges on the walls, because the absorbing boundary condition removes the particles. Is my understanding incorrect?
2. In the Diagnostics section of WarpX, the data list includes ‘rho’, ‘E’, ‘B’, ‘J’, ‘Ex’, etc. Does it include an output for the potential, as it is not mentioned on the webpage?
3. In this case, can I set a specific number of particles in WarpX? Can I use n_macroparticle_per_cell to represent the number of particles per cell and thereby obtain the total number?
   These are the problems I'm currently encountering. I would be extremely grateful if they could be resolved. Apologies for using a translator.

[RemiLehe]

Thanks for raising these questions @AGreatDayForReal

Regarding 1: you are correct that, by default, WarpX is unable to simulate the potential changes caused by particle absorption (at least when using an electrostatic solver, which I assume is what you are using here), because particles are absorbed at the wall and then "forgotten". In order to simulate a floating potential at one boundary, you need to count the charge that accumulates on the wall and correct the potential accordingly, e.g. by using Python callback functions. This is done for instance in this example but for particles that accumulate on a sphere, so it uses a geometry that is quite different from the one that you are interested in. But in principle you could adapt this script so that it runs in 1D geometry and conforms to the problem that you are interested in.

Regarding 2: if you use the labframe electrostatic solver (see warpx.do_electrostatic = labframe), you should be able to see phi (which represents the potential) in the output. If that's not the case, feel free to share your input script here so that we can take a closer look.

Regarding 3: You can indeed use n_macroparticle_per_cell to represent the number of particles per cell. If you have more question on this point, maybe you can share your input script to clarify your question.