The gauging may mean nothing at all in strict fusor operation and I say this as a person who has an intrinsic "feel" for fusor operation.
This is why I strongly urge everyone to do a demo or air fusor first.
Pump down and glow cleaning are a process which should need no meter.
1. turn on the vac pump
2. After some time , maybe 5 minutes, apply voltage to the fusor slowly with a variac or other voltage control. get a glow discharge. Q. Is the glow large and lumpy with porcupine quills out of every port on the inner grid? Yes - Forget it!! If you have pumped for 5 minutes you pump ain't cuttin' th' mustard, or you have a serious leak. Correct and start over at 1. No - If the glow is large, smooth and diffuse with maybe one dancing, bright, e- beam, you are on your way. go to 3
3. Keep the current under or at 20ma, but no matter what, prevent the grid from glowing red hot.
4. Read the voltage. Q. under 5kv? Yes - You are no where near 20 microns yet. Let it pump more and keep the current at or below 20ma with the voltage control - go to 4. No - You are now over 5 KV - go to 5
5. Q. over 10kv? Yes - You are getting there and will soon be at the operating point. You are now below 10 microns. It is important from this point on to forget the current value, per se, and run the system with the grid just barely red hot (dark red) You might see faint star mode rays. Go to 6. No - Continue to pump and up the current only slightly until the grid just starts to turn red. Let the current go where it wishes, but just keep the grid from getting too red hot. This will hasten glow cleaning and water expulsion. If you do this for 10 more minutes and you are still under 10kv on the voltmeter, then you will not reach operating range. Most likely, You have a leak or bad pump. Shut down. Find and correct problem. Start over at 1.
6. Q. over 15kv? Yes - You are almost ready to start introducing D2. remember, You must from this point on make micro voltage increases as the grid should now be getting quite hot. Keep the grid from getting in a runaway situation. The hazy glow about the discharge in the inner grid should be clearing away now and the crispness and contrast of the glow should increase. Rays for sure now, I hope. Go to 7. No - Keep it up and you should soon be at 15kv if your pump is good. If this is a first run or if the chamber has just been let up to air and is back in use, then it might take a bit longer to pump dwon and unload the water adsorbed on the chamber walls.
7. As the voltage approaches 20kv, you are now ready to leak in d2 very slowly. Turn the power supply down to about 5 kv., (glow should exinguish.) Let in a micro amount of d2 via a leak or such valve. If the glow snaps back on instantly, then reduce the d2 flow until extinction again occurs. Now up the voltage slowly until glow is seen. If it occurs around 15 kv then you are OK.
From this point on you are on your own. D2 may have to be cut back more if you can't quite hit 20kv without running the risk of a grid meltdown.
Tweeking and fiddling, you should be able to hit 25-30 kv in about 30 minutes. All during this time you will be fighting extinction in "anomolous pulse discharge mode" (ragged edge of glow mode) and trying to avoid grid melt down or runaway electron emission from the inner grid.
The signature current in the 25-30kv region is about 5-10 ma. If you have a neutron counter present, you should notice definitive neutron detection as low as 15-20kv.
So, without any reference to vacuum gauging, we have a fusor up and working based on observations and appropriate adjustments of voltage, current, the discharge appearance and the inner grid temperature.
Richard Hull
Created on Monday, May 21, 2001 11:49 AM EDT by Richard Hull