|The focused spot of the beam profile. The Einzel focusing|
lens will focus particles with a specific charge-to-mass ratio
into a beam as seen
|The halo of the beam profile. Due to the non-constant|
charging process in the source, the charge-to-mass ratio of
each particle can vary greatly. This leads to this unfocused
halo around the focused spot.
The reason for the central beam and the halo has to do with the way the dust source works. This particular source does not charge every particle the same, so the charge-to-mass ratio is not constant across all the particles. The focusing of the beam on the other hand, is dependent on the charge-to-mass ratio. What we would expect is that a majority of the particles will be charged to the same charge-to-mass ratio, giving you a well focused central beam, but then the rest of the particles will end up in the diffuse halo around the central focus.
I'll be continuing these studies into next week and hopefully will have more updates for you by then.