by Doug Coulter » Tue May 31, 2011 9:41 am
Glad to see it made the trip -- these should, they're pretty solid the way we made that one.
We did go away from flow-through gas. I'd made a coupling of pyrex tubing a little over a foot long to isolate the gas electrode when I did flow through gas, but under some conditions that would light up and short the push power to ground, so I quite doing that. Since I've gone to batch mode, the pressure in the supply line is about atmosphere during a gas pulse, but then goes down to eventually the tank pressure as the gas goes through the thing. At some point it finds a Paschen minimum and lights up like a neon tube, shorting the pusher supply to the grounded tank plumbing. Never seems to happen at a convenient time. In experiments, I found out that once lit, you didn't need the extra gas in the source to keep it lit if you were willing to fire it up while the gas pressure was still on the high side (e-2 or e-3) and it would still stay lit to almost e-6 mbar soooo...simplification is good!
You do get some short UV off D, but it should not be much as you should only be making ~20w of RF in the first place and that just won't make that much light. A regular-glass or plexiglass shield should eliminate concerns.
I don't have a lot of microwave leakage here on my (cheaper) leak detector. I'd guess either an endcap is a bit loose or that the length of rod for the pusher is resonant at this frequency if you're seeing a lot. On the other hand, mw/sq cm isn't a lot if it's in a small place and you're not pressing your eye up against it. Were it a watt, I'd be more worried. It obviously matters a lot more if it's high where you are at, or jams your wifi (same frequency, which is why it's used for that - no license needed).
One thing most people don't realize is just how low the percentage of ions is even in this, or in a fusor running full bore. As an experiment sometime, let in just a little too much gas (on my gage that would be about 2.5e-2 mbar). This will cause any reasonable current limit to be hit, in my case around 20 ma at about 40kv. Well, I have this super high power supply so I can crank up the current. Guess what -- the voltage won't rise even going all the way up to 50ma - you just ionize more of the neutrals and the voltage stays depressed!
That's one of many reasons I'm going to build a deliberate beam-linac device, so as to run in "pure" ions, not a mix of ions and neutrals and electrons.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.