More Plasma

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
John Beutz
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More Plasma

Post by John Beutz » Sun Sep 18, 2016 5:21 am

Close up of more plasma at higher voltage.
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John Futter
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Re: More Plasma

Post by John Futter » Sun Sep 18, 2016 7:03 am

Nice pics
Vacuum needs to improve by a hundred fold so you can photograph bugles and star mode

John Beutz
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Re: More Plasma

Post by John Beutz » Sun Sep 18, 2016 2:17 pm

Yes, the vacuum isn't very good with my current pump and chamber. Next on my list to buy is a better pump and a thermocouple gauge so I can compare the pressure in the chamber and the pressure when I connect it directly to the pump.

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Rich Feldman
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Re: More Plasma

Post by Rich Feldman » Sat Sep 24, 2016 1:38 am

Your action items are out of order, John.
New pump and thermocouple gauge won't improve your plasma, I bet.
Fixing your vacuum leaks will give you better results, sooner, for less money. You need to fix them anyway. Pump sound and plasma appearance are the only gauge you need at the present level of leakage. Plasma voltage measurement would be a plus. There are many practical hints in the forum archives.
Mike echo oscar whisky! I repeat! Mike echo oscar whisky, how do you copy? Over.

John Beutz
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Re: More Plasma

Post by John Beutz » Sun Sep 25, 2016 9:52 pm

Rich Feldman wrote: Pump sound and plasma appearance are the only gauge you need at the present level of leakage.
Yes, the pump had been running loud for the entire time. Should have noticed that sooner, there are clearly leaks. I also realized that I haven't cleaned the thing and reapplied vacuum grease since I first put it together. New pics coming soon, hopefully with some progress.

Thank you for your advice, I will update my to do list accordingly.

John Beutz
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Re: More Plasma

Post by John Beutz » Mon Sep 26, 2016 12:49 am

I let the pump run for about 10 minutes, and fixed some major leaks (loose nuts, loose hose clamps, lack of vacuum grease). Still only seeing marginal improvements.
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Richard Hull
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Re: More Plasma

Post by Richard Hull » Mon Sep 26, 2016 7:50 pm

Sorry to say.....That is not even hardly a vacuum at all... maybe 5 torr. A good vacuum is about 1000 times deeper.. I think a good hand operated pump could do better. If you are really sealed well, then you pump is bad...really bad. However one would like to think it is a sealing issue. Without a TC gauge, you are totally in the dark and might never know if it is a leak or your pump.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Rich Feldman
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Re: More Plasma

Post by Rich Feldman » Mon Sep 26, 2016 9:30 pm

I respectfully disagree, and am not completely without experience in this department.

Sure, it would be a big help to have a thermocouple or Pirani gauge connected. You need one anyway, sooner or later. But the leakage (?) today is so bad that primitive, gauge-less methods can suffice. As said before, novices tend to erroneously blame the pump instead of their home-built chamber and plumbing. Do not buy a new pump before proving that the one you have is no good.

With plasma lit, John could close a valve (e.g. ball valve) between pump and chamber, or use a vacuum hose that can be kinked or pinched shut. Doesn't need to be a super tight closure. Then, if the trouble is from a leak on chamber side of the closure, the chamber pressure will rise rapidly & plasma will change accordingly.

I also learned from experience that gross leaks can be briefly plugged with vacuum pump (or thicker ) oil, or vaseline, slathered onto the outside of joints with something like an acid brush. Do that while plasma is lit and pump is running, and watch plasma for sign of pressure dropping. Eventually, outside air will force the oil through to the inside of leak, and you may be able to see bubbles forming. There are many places where you might have a leak: both ends of clear cylinder, threaded end plate joints for HV, pump, and gauge; hose end; useless Bourdon-tube gauge itself (could be replaced with threaded plug); HV feedthrough places where dielectric meets metal. Don't be afraid to make a mess! Where I ran into trouble (reported here long ago) was with a clear plastic bell jar and a stiff plastic baseplate. Baseplate deflection under vacuum made some of my feedthroughs leak.
Mike echo oscar whisky! I repeat! Mike echo oscar whisky, how do you copy? Over.

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Richard Hull
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Re: More Plasma

Post by Richard Hull » Tue Sep 27, 2016 1:54 am

A $5.00 ball valve in the line would do the trick. So many folks come to this game without any good instrumentation and not one single valve in the system and wonder why they can't get a good glow or track down issues. Vacuum is more than a pump, a hank of hose and a chamber.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

John Beutz
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Re: More Plasma

Post by John Beutz » Tue Sep 27, 2016 3:50 am

Update on this afternoon's progress:
Rich Feldman wrote: With plasma lit, John could close a valve (e.g. ball valve) between pump and chamber, or use a vacuum hose that can be kinked or pinched shut. Doesn't need to be a super tight closure. Then, if the trouble is from a leak on chamber side of the closure, the chamber pressure will rise rapidly & plasma will change accordingly.
Richard Hull wrote:A $5.00 ball valve in the line would do the trick.
After a quick trip to Menards, I got a ball valve and some threaded tubing attachments for it. I clamped it all together and attached it to the pump and the chamber.
ball valve.jpg
When I turned the valve to off with the vacuum having been on for about five minutes and an acceptable plasma glow on my thicker (and most poorly made) grid, the needle on the gauge slowly moved to the left. Notably more slowly than when the pump was simply turned off. More importantly, the plasma was gone in seconds, even at 3/4 variac output, just as Mr. Feldman said it would if there was a leak in the chamber.

Here's a video of the process:

https://www.youtube.com/watch?v=sAuKoV0 ... e=youtu.be

Next, I followed the next piece of advice:
Rich Feldman wrote:I also learned from experience that gross leaks can be briefly plugged with vacuum pump (or thicker ) oil, or vaseline, slathered onto the outside of joints with something like an acid brush. Do that while plasma is lit and pump is running, and watch plasma for sign of pressure dropping. Eventually, outside air will force the oil through to the inside of leak, and you may be able to see bubbles forming. There are many places where you might have a leak: both ends of clear cylinder, threaded end plate joints for HV, pump, and gauge; hose end; useless Bourdon-tube gauge itself (could be replaced with threaded plug); HV feedthrough places where dielectric meets metal. Don't be afraid to make a mess!
I certainly did make a mess! The borosilicate was all greasy after I put a great amount of leftover vacuum pump oil on the places where the glass intersected metal. I also put some on the HV ceramic feedthrough, and the threads of the gauge and tubing inlet. It's hard to tell if the pressure improved; the gauge is, of course, useless, and the plasma showed no significant change. However, after less than a minute, large amounts of bubbles were forming around the screw on the HV feedthrough. Thank you for that piece of advice! I tried to get a photo, but the chamber was so covered in oil so I couldn't get the camera to focus on the inside.

Thus, based on what Mr. Feldman said, I suspect the leak may be in the feedthrough. Perhaps there are even leaks in the ball valve. I guess there may be because it wasn't built specifically for this, but I made very sure to tighten the hose clamps. Also, because of the placement of the vacuum inlet tubing, I cannot fully tighten the gauge on top. Is that threading a potential candidate for leaks? Either way, that gauge has got to go; I'll replace it with a threaded plug as soon as I can get back to Menards. Probably tomorrow. I may also get some Teflon thread tape to further secure the threads.

And, as always, I am continuing to solder new grids to hopefully improve the geometry, even if that only marginally increases plasma.

- John

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