Neutral (zero charge) particle's momentum get updated by field in 2D simulation

[GivenChen]

Hi, I am not sure if it is a bug... I found it very strange that in my 2D simulations, all neutral particles are pushed by the grid field(as if they have +e charge), but actually, they are not ionized and have zero charge. Here is my simulation result: I am simulating an electron beam(initialized between -100cm to 0cm) passing through a region full of neutral hydrogen gas(initialized from 0cm to 70cm).The hydrogen gas particles are not ionized but somehow pushed by the electric field from the beam.

The hydrogen species charge distribution: It is zero everywhere---meaning there is no ionization

The average hydrogen momentum distribution(particle field ux of hydrogen species): They gain momentum somehow

I am very confused so I checked the source file, it looks like this line controls the ionizable particle's charge:

So I did a little test and changed the line. I subtracted the ionization level by 1 here

The result is simulation result didn't change at all.. So my guess is that ion_lev is not updated and remains null pointer?

Any help would be highly appreciated! I will attach my input file in the following as a txt file, and the Warpx version is the latest release 24.01.

inputs_2d.txt

[ax3l]

Hm, this seems to be a bug. Let's move this to an issue:
#4592