Fusor pump down after five years

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Dennis P Brown
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Fusor pump down after five years

Post by Dennis P Brown »

Well, assembled the remaining parts and pumped the fusor down; held about 60 microns with just the fore pump. Bad but enough to allow the diffusion pump (DP) to start up. I allowed the DP to heat up then started the water cooling of its upper stage. After ten minutes the pressure dropped rapidly to between 1 and 2 microns. After two minutes of burping gas, went off scale; however, never low enough for my ion gauge to kick on.

Closing the gate valve for the fusor caused the fusor to rapidly rise past 100 microns in seconds. Likely a small leak. So, that will be a job for this weekend - locate the leakage issue. Still, working better than I feared. Hope it is a simple issue and not the electrode - that would be a pain to deal with.

At least I'm finally using my new lab "shed" for something other then storing all my research equipment. :)
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Fusor system being pumped
Fusor system being pumped
Fusor w/o DP, just fore pump
Fusor w/o DP, just fore pump
Fusor body below reading of the TC with DP hot
Fusor body below reading of the TC with DP hot
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Richard Hull
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Re: Fusor pump down after five years

Post by Richard Hull »

Good work in getting the assembly up and running. If you didn't have this leak before, I would suspect a less than satisfactory coupling to the fusor body among the items directly connected to it.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Dennis P Brown
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Re: Fusor pump down after five years

Post by Dennis P Brown »

Agreed, Richard; so I decided to check the main o-ring on the upper part of the fusor since that is a new adaption*. So I removed the o-ring, cleaned it and the surfaces; then applied vacuum grease to the o-ring, wiped the grease off, and replaced it back into its grove; then I ran the system again and it got down to 35 microns - still poor but better. So I tried running the diffusion pump and did managed to get the ion gauge (well, cold cathode) to read. This too is poor for the setup; previously, bottoming the 10^-5 torr scale was more typical. When I sealed off the chamber the micron gauge ran up slower this time (but still, far too fast), so I am making some progress but still, something is amiss.

Now that the 'ion' gauge reads, I did try alcohol but didn't really see any big changes - the scale did go up a number or two but no big jump. Still, might need to disassemble the entire upper fusor and check all the parts. But before that the electrode will be my first point of interest in the next go round.

Of course, right in the middle of this experiment a waterline sprung a leak - and of course, it was the main feed into the DP. So I was forced to shut the water off and rapidly cut off that old ferrule, and install a new one. Managed with only a very minor and superficial burn ... the DP lower region is hot. Guess that is why it is water cooled.

*Teach me to chase fades ...my old system was tight AND water cooled but no, I had to replace it. Ugh - what was I thinking** :(

** Ok, I wasn't
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Ion gauge reading
Ion gauge reading
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Richard Hull
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Re: Fusor pump down after five years

Post by Richard Hull »

One of life's lessons often forgotten and just as often re-learned......"Let a sleeping dog lie".

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Peter Schmelcher
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Re: Fusor pump down after five years

Post by Peter Schmelcher »

Dennis get a can of Dust Off. I posted years ago about painfully looking for a vacuum leak using alcohol and finally finding leaks using Dust Off with an inverted magnetron. The leak detection process should work for any pressure measuring process that fragment's the Dust Off molecules into atoms.
-Peter
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Dennis P Brown
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Re: Fusor pump down after five years

Post by Dennis P Brown »

Richard, so true and again, I didn't and I got bit.

Well, something else I forgot and absolutely correct about 'Dust Off"; just pays to post here and get such good advice.
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Dennis P Brown
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Re: Fusor pump down after five years

Post by Dennis P Brown »

Continuing work/progress on the new fusor. So I started the fore pump and it moved the system/chamber down half as much again (12 microns) as yesterday's best effort. That again is an improvement solely due to the previous pumping and over night cooling under vacuum. So certainly out gassing is a significant issue (but not the only.) The upper chamber was open to the air for five years (oops, didn't realize that till I brought it out from storage. The DP and lower section were still under vacuum.) Closing the gate valve (DP is off) the upper chamber rises too fast but again, at slower rate then yesterday so still an improvement.

Well, fired up the DP and the unit quickly bottomed out to 2-3 x 10^-4 torr. After a few minutes of pumping the chamber hit the mid 10^-5 torr!

As per the suggestion, I then used some Dust Off and discovered that everything is tight (including the electrode) except the deuterium inlet assembly. So I tighten all the components related to that system and now no response from that assembly to the Dust Off. So that was a minor leakage issue for sure. I guess now it is mostly (all?) just out gassing so I'm gonna let it pump for a while at the mid 10^-5 torr.

If I get the chance, I'll finish the power supply and using a safer voltage (15 kV or so), try to burn out the chamber using that plasma (air, of course. I'll save my deuterium only for real fusor work!) However, before doing that burn off, I will certainly install a real (old style) ionization gauge - I don't trust the plasma to not damaging the cold cathode - the TC is (partly) protected by a metal screen. I only use the cold cathode system for calibration and safe (read, no plasma and fairly clean) vacuum work. Holding around 30 - 100 microns min should ignite a good plasma glow.

Aside: since it is only the upper chamber that was exposed to excessive water vapor over the years (maybe a small spider or two), the fact that that will be the only region really exposed to the plasma should enable the necessary cleaning of the chamber interior of water vapor and mic. carbon based substances. So, hopefully, I wont have to figure a way to bake out that chamber.
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Thermo-couple Gauge Reading using just the fore pump
Thermo-couple Gauge Reading using just the fore pump
DP hot and running
DP hot and running
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Dennis P Brown
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Re: Fusor pump down after five years

Post by Dennis P Brown »

After cool down, I installed the high voltage (HV) lead; then pumped the system down and the lowest fore line only pressure was half again as low as before - this time about 6 microns on the fore pump.

I ran the power to about 10 kV and let the system "ash" the chamber for a few minutes. I'll see what this allows for any new pressure read - more importantly, the rise time when I close the gate valve isolate the fusor chamber.

The current ran (max. out) over 50 ma at 15 kV. So I had to back it down to 9-10 kV to hold 28 ma or less. This surprised me - I expected at that pressure to run a higher voltage. The old fusor easily ran 30-33 kV at 28 ma in the 6 to 10 micron range. The smaller chamber apparently makes a huge difference. Not expecting that result. Maybe I need to make a smaller cathode for the chamber. Might try that - any other suggestions for why my current is so high for a lower voltage but similar pressure as before? Maybe I just need to clean the glass of the sputtered metal - that, at least, will be my first try.

Sorry but no matter how I flip the original photo's, those last two always end up side ways.
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Chamber pressure with the fore pump only
Chamber pressure with the fore pump only
Plasma in Chamber
Plasma in Chamber
Fusor chamber with electrode
Fusor chamber with electrode
Current and voltage
Current and voltage
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Dennis P Brown
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Re: Fusor pump down after five years

Post by Dennis P Brown »

Well, learned a lesson - first, small chambers aren't easy (no fusor is but these are wicked.) Second, not cooling my ballast resister even for short runs is a terrible idea. Third and finally, having a properly rated fuse for one's transformer is a critically important thing (glad I did.)

After cleaning the glass, and making a small electrode I tried running the system. Again, 13 kV at best with max current of 28 ma. Required about 1.5 microns to run 32 kV and that was both touchy and hence dangerous to my electrical system. The system spiked and blew both the transformer fuse and my ballast resistor. But the transformer was safe and that is all that really matters - (current far exceeded 100 ma for a second.)

I quite with this system - no way I'm using that small chamber again - period. I will have to replace my big chamber (the original was junked - not bright) and go back to my original system design. I will have to look for a suitable large chamber and get a proper electrode for what-ever-design the next chamber requires. Till I do all that, I will not do any further fusor work with this small chamber system. I'll certainly keep the system under vacuum and even test it from time to time. But adding a new chamber will be a lot of extra work and delay my activation work till ... well, till I get the new chamber installed.

Finding another proper ballast resister isn't gonna be easy, either.
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Richard Hull
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Re: Fusor pump down after five years

Post by Richard Hull »

Small 2.75 cross, for me, was crap! Really tried hard to get it to play. It did fusion, but just couldn't get it up to even 1/8 of fusor IV. Arcing was an issue, and I just went back spherical. Like I say fusion is....or should be, easy. Bought a 6-inch 6 way cross....Don't think I'll be using it. What will fusor VI look like? Larger cylinder maybe?

Good luck getting something bigger set up.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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