Distribution of protons in momentum space in an ion source?

[Sven Andersson]

How are protons in an ion source distributed in momentum space? Consider an ion source fed with H2 at low pressure. As soon as the protons are free protons they are accelerated by the extraction voltage of perhaps 10 kV. In momentum space the protons are initially a "shell" with a certain diameter and thickness, like in the picture below. Let's say that the extraction is along the y-axis, so to speak. Then that "shell" moves to the right in the picture as the protons are accelerated. But continously new shells should emerge at the origin as H2 is ionized. And collisions will also create new populations (larger shells?) in momentum space. How can a complete description be formed of this?

 

[mfb]

In momentum space the protons are initially a "shell" with a certain diameter and thickness

That will depend on details of your source, but I would not expect an empty shell for any source.

Then that "shell" moves to the right in the picture as the protons are accelerated. But continously new shells should emerge at the origin as H2 is ionized.

Sure, but those are also displaced in position.

And collisions will also create new populations (larger shells?) in momentum space.

Whatever structure you start with will get smeared out a bit over time. Other effects are relevant as well, like your field geometry.