23-12-2020, 09:15 PM
I've actually heard of gas being used to IMPROVE focus.
High-energy electrons, travelling fast towards the screen, knock electrons out of the gas atoms in the path. This leaves a pencil-like 'core' of positive ions at the centre of the beam.
This 'core' of positive ions, then attracts wandering electrons back towards the centre of the beam (electrons, being negatively charged, repelled each other so an electron beam, unlike a ray of light, naturally diverges anyway).
I can quite believe that the undesirable other effects of gas easily outweigh the focussing effect, but - does this happen, and how much pressure is needed?
High-energy electrons, travelling fast towards the screen, knock electrons out of the gas atoms in the path. This leaves a pencil-like 'core' of positive ions at the centre of the beam.
This 'core' of positive ions, then attracts wandering electrons back towards the centre of the beam (electrons, being negatively charged, repelled each other so an electron beam, unlike a ray of light, naturally diverges anyway).
I can quite believe that the undesirable other effects of gas easily outweigh the focussing effect, but - does this happen, and how much pressure is needed?
