Fusor Forums

I'm interested in any pictures or diagrams that anybody has of professionally made or mass produced electron impact ion guns.

(these are more common in RGAs and mass spectrometers, which is what I am building, than in things like fusors.)

Mass spectrometer electron impact ions sources tend to be of relatively simple construction. I’ve worked on dozens of different ones in my forty plus years in that business. They are essentially a box (“ion volume”) with an ion exit hole usually orthogonal to the electron beam, which is provided typically by a rhenium ribbon filament that sends electrons into the box via a hole. Typically, a collector (the“plate” in tube language) is located on the opposite side of the box with an electron exit hole. The box may be made of sheet material or machined from stainless steel (non magnetic variety). Many use permanent magnets to provide a magnetic field parallel to the electron path to make the electrons spiral, thus increasing the path length and probability of collision, but this is less common in RGA sources. There are usually some lenses after the exit hole to focus the ion beam.
A good place to find pictures of ion source components is the online catalog of Scientific Instrument Services. They sell parts for a wide range of mass spectrometers and RGA’s. You can also find manuals posted online that would include photos and assembly drawings. The nemesis of EI mass spectrometrists is cleaning ion sources; the manuals give assembly information because use involves lots of disassembly and cleaning. This is less an issue with RGA’s since they tend to run cleaner.

I have gotten so far as to pick up on the "box" structure of these ion sources.

I'm curious whether you have a clear idea of how the gas is injected -- is there just a tube going into the side of the ion box? How large would you say the exit and entry holes typically are? Are they equal to each other?

The ion sources I’ve worked with were typically about a 15 x 15 x 10 mm “box” with the ion exit hole centered on a 15 x 15 side. The holes were on the order of about 2 mm diameter. For RGA’s, the “box is more open to sample the vacuum environment. For externally introduced samples, an insulating tube leads the sample into the box.
I’ll try to find one and post a picture.