We’re slowly inching towards an electron gun test. We want to make sure everything works before trying it, because repeatedly sealing and unsealing the chamber is not only a pain in the ass, but includes the risk of contamination/damage to the inside of the chamber.
But I think we’ve really got it this time.
I simplified the armature. It’s now one piece that attaches to a ceramic column which screws into the eight-inch conflat flange on the chamber. I also switched from the big ceramic light bulb socket to a smaller, lighter one.
Much easier than the three-piece setup I had before, and its still somewhat variable; the distance between accelerator and cathode, and Langmuir probe and accelerator are both variable.
Closeups:
The accelerator anode is very close to the hot cathode
The Langmuir probe
I also made a couple of changes to the power supply. We found that the high voltage box which we were going to use to give the accelerator it’s high positive potential has a built in potentiometer:
So we don’t need the extra one. I also made a piece which holds the HV output wire in place:
it’s a cylinder with an inside diameter the same size as the piece on the HV box, so the threads dig into the plastic and hold the HV out in place
The updated schematic:
So the electron gun seems to be totally ready for a test.
Here it is in the chamber, viewed from the glass on the other side
Hopefully we’ll be able to do it in the next couple of days. One thing I’m worried about is the interaction between the beam and the accelerator. Will the potential on the accelerator sag because it is being bombarded with electrons? Another worry is how vacuum compatible this whole assembly is. Probably not very, but thankfully, vacuums don’t need to be that deep for electron beams.
This is a very exciting moment, because if this works, we can start thinking about how to make it more powerful. If we succeed there, we will be able to use an electron gun to deepen our potential well, which is uncharted territory.
Domenick Bauer
Prometheus Fusion Perfection 
It may be completely unfounded, but my only fear by looking at the setup is it looks like there would be a lot of de-focusing of the electrons between the cathode and anode. Do you expect the cylindrical base of the bulb to add some focusing field?
Interesting application, Your electron gun is going to have a positve potential riding on your filament? How is that to repel electrons?
I find your setup interesting. Thank you for sharing such detailed information.