I have a 2mx15cm tube attached to a 1m3 chamber:
I would like to understand the beaming effect that gets created in the tube: supposedly with a relatively long tube almost all particles should be perpendicular to the tube cross section and hit the opposite wall in an small circular area. Which is more or less what I’m seeing:
To determine the number of particles desorbing in each direction I used the “incident angle distribution” option on a transparent circular face placed between the two zones. And this is the resulting distribution of the particles based on the theta angle:
I’m confused by this graph. If theta=0 is the normal of the plane I’d expect a concentration of particles around this value, while it almost seems like particles around this are almost zero. It looks like most of the particles cross this surface with an angle around 0.4rad = 23°, and thus they should end on the side walls rather than on the front wall.
Am I misinterpreting the results of this graph? Or is there some other parameter I’m not taking into consideration?
This is the study:
beaming.zip (425.1 KB)