Yes, it's a
big deal to get from a pile of parts to a glow, as you guys now know!
Your pictures show the same thing mine do when the pressure is too high, and I also see 500-1000v on the grid proper under these conditions. We also see the little "bugle" formations here while pumping down from too-high pressure, and if they appear at random and move around, you've got a good uniform grid. If they're always at the same place - not so much. You'll rarely need to run over about 15 ma in real life with a fusor this size (and you'll need some fan cooling on the resistor to do that for long). Here we find our best output of neutrons when we set our supply (at full voltage) to limit around that current or a bit less, then adjust the gas pressure to stay under that limit, running about 10ma average in our setup for best output in our "normal/static" mode.
We've had no troubles due to grid heating here up to the point of melting a Ti one at about yellow heat. If anything, that cleans them up and gets rid of any gas they had ad or absorbed. You just need to be sure you're not hurting the end of your HV feed through with heat, which shouldn't be much problem -- it's fat and leaves the tank so it can take
some heat out with it.
I've been able to use compression fittings fine, but most people don't understand at first just how perfectly clean and correctly formed it all has to be to work right. Heck, I've even used flare fittings, like the plumbing kind, but again -- have to do it just so. There is a flare fitting in my D
2 supply (provided with the regulator) and it doesn't leak at all. I've had probably less trouble with Lesker than you've had with your vendor, but no one is perfect. The prices are all so high we get most of our stuff elsewhere anyway -- ebay and general scrounging (sometimes at the Va Tech auctions!)
I suspect you're going to need another stage of pumping -- diffusion or turbo. The situation is that if you could get the actual nameplate ratings of a typical 2 stage vane pump, you'd be fine, but that never happens even in a leak tight system, even after baking it out and pumping overnight. They rate these with a big degree of "specs-man-ship" to say the least. Any HV pump will then be far too much -- but that's what valves and bypasses are for. A good pumping system will cut down your outgassing time considerably as well. If you have trouble scrounging a HV pump on your budget, get in touch as we have some spares here. Right now, you're working on the lowest bottom of the
Paschen curve -- you need to get over to the steep left side of it. At a too high pressure, you can indeed get to an arc, and
the mean free path is such that you can't get any ions up to full speed due to collisions with neutrals -- and with too much gas, you can't ionize it all with any current under a lot of amps.
Strictly speaking, an arc is the lowest voltage and highest current mode, like a welder, and that's not what you have here, you simply have a normal glow discharge (which is good).
You can find some good information, along with
correct terminology here, in the Phillips book. The first couple and the last chapter (with a neutron generator design) should help you there.
Congrats, you're on the way now!