It's interesting that even though we should be making a line focus, everything in the poisser and rays tends to concentrate on the middle of the grid - and that's even despite one end being really near the end of the sidearm, and seeing a wierd field gradient due to the larger tank at that end, vs the end nearer the feedthrough deep in the sidearm. No, I don't know why...
Here's a pic from the top with the lights on, just so you can see the basic configuration. The ion source grid doesn't show here, but it's off to the left.
- What it looks like with the stab-n heaters on for reference
Now, running almost full snot - reduced current and about 45kv instead of the real hot running conditions. I don't think that makes any difference in how this looks, but running full-out definitely is more rads to the camera and cameraman.
What happens at just a little higher gas pressure is lower voltage current limiting (even though we have up to 40 ma available) and fuzzier rays - it seems like more than just a mean free path effect, since that's about the difference between 2.2e-2 mbar for the low end, and 2.5 e-2 millibar when it's full out limited - and fuzzy, and making few neutrons.
- A pretty real situation, about 2m neuts/second here
The beam out of the end looks a little fanned out to the left, where the ion source grid is. Funny thing, it's the same polarity and ought to bend things away from it. That's what we see when we run hard enough to make the stainless steel screen over our viewport directly opposite the grid-end get hot enough to glow - so whatever is smearing here isn't the stuff that has the real energy in it.
Edit, that blue glow in the bottom is some ZnS:Ag I spilled in there years ago. It doesn't take much (can't see it in the light) to make that much glow when it's that "hot" in there. We used to have a BGO crystal in there too so we could see X rays etc, but it was so bright it interfered with taking pictures.
Edit: Bonus picture end on under the same conditions. You can see the glass inside the tank fluorescing even though it's behind a dense SS screen that's grounded. We see a red hot spot when we run high enough current, and it bends *away* from the ion source grid when that is energized.
- End on view, through 3 pieces of glass (two leaded for my safety, but that's why the reflections)
