Problems of readig particles from_file and freezing particles

[15630027895]

Hello, I would like to ask two questions;

1. When I run an input file, I take its output result at a certain time as beam.injection_type =from_file beams.input_file. In the next moment, the output of from_file is different from the output of the original input file in the next moment, I would like to ask what causes this?
2. I want to know how to freeze particles? I want to realize that at some point (or distance) before the particle is in the window, but frozen, until after the driving beam has evolved for a certain amount of time, the particle begins to be affected by the field. To achieve functionality similar to the one shown in bold below.
   For species injected using this method, particles are translated along the +z axis with constant velocity as long as their z coordinate verifies z<zinject_plane. When z>zinject_plane, particles are pushed in a standard way, using the specified pusher.