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Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 6:52 pm
by Richard Hull
That might be one of the best looking chambers to be presented here in years!! Keep us up to date on your progress. I am fairly sure that there is a significant UV component in a fusor. Vacuum UV can only be found in such systems. Any dangerous UV would never leave the system, of course, without a Quartz window.

All the best in getting this plus-ultra system on line.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 9:32 pm
by Silviu Tamasdan
Well _some_ UV is bound to escape, depending on intensity and wavelength. Glass is to UV what lead is to gammas, they get attenuated but not completely absorbed. That's the problem with photons, you can never get rid of them completely.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Dec 24, 2017 10:06 pm
by Dennis P Brown
Regular plate glass cuts off essentially all hard UV (UV-B) and one need not worry about that spectrum at all (say about 330 nm and shorter.) That said, do be aware that both UV-A even to Blue-Green ... say down to 450 nm can be harmful to the eyes (apparently, the new very white LED's street lights can damage the eyes); however, little of those wavelengths are usually produced via a plasma in a fusor. If one is using a Hg source, plate glass is rather effective cutting off most the harmful wavelengths.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Dec 25, 2017 2:46 am
by Jim Kovalchick
Final holiday update
I used a helium leak detector to locate some CF torquing issues, but a fairly bad leak remained. I never thought to pass a little helium over a KF 40 bellows hose I was using to connect to my turbo. When I finally hit it, it was a huge hit on the leak detector. I have temporarily replaced it with hard pipe. I was able to remove the leak detector and roughed the chamber to less than 10 mllitorr in five minutes. Isolated, the chamber rises less than a milltorr a minute. This is all before any bake out. I think my chamber is ready for plasma.

Next steps after the holiday - clean up the construction mess to make the lab safe, get my power supply ready, and get some current and HV indicators attached.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Dec 25, 2017 12:21 pm
by Dennis P Brown
Yes, bellows can be a tricky issue since they are easy to overlook; while sorry to hear that, still, I am glad you have a tight system now - the bake out will certainly and dramatically lower the out gassing rate. I use dry air to purge my accelerator to better enable it to get into the low vacuum range more quickly; that or argon might be useful for your chamber if you decide to go ultra high (below 10^-6 torr.)

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Dec 25, 2017 6:16 pm
by Richard Hull
Great work and what a beauty. That is a system to be proud of. I'll bet it will kick butt and easily hit the mega mark with ease in the 35-45 kv range.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 26, 2017 5:39 pm
by Jim Kovalchick
First light for this chamber.

1. Started at -8 kV with air.

2. Walked voltage to - 17.8 kV holding about 8 mA.

3. Need to rework HV cable because I heard some ticking from the cable near tbe feed through at peak voltage. Probably dont have the shield stripped far enough back.

4. One of my grid wires shifted a little when it warmed, but otherwise there was only minor and brief arcing as I stepped voltage.

5. I don't think this is a surprise to anyone but the uranium glass marble did glow a little. The glow doesnt show up well in the photo.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 26, 2017 7:07 pm
by Dennis P Brown
I discovered the hard way that 30 kV will go a long way along an insulated cable and reach the shielding strap (and I had carefully cleaned the cable after striping away the shielding); a good four inches was needed, so I ended up removing 8". In the HV cabinet, I even placed the cable end under oil for the ballast resistor connection to play it safe.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Tue Dec 26, 2017 7:34 pm
by Jim Kovalchick
Dennis,
I just atripped back about 8 inches where there was only 4 before. This seemed to do the trick up to -40 kV. This is the highest voltage I've ever spent any time at. It made a nice tight spot of plasma.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Wed Dec 27, 2017 3:38 am
by ian_krase
Allegedly, folding back the shield, possibly over an O-ring or similar, rather than just cutting it can also help. That is what I did, and while I had corona I never had arcover at 50kV just from the end of my cable.