More Plasma
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- Real name: John Beutz
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More Plasma
Close up of more plasma at higher voltage.
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Re: More Plasma
Nice pics
Vacuum needs to improve by a hundred fold so you can photograph bugles and star mode
Vacuum needs to improve by a hundred fold so you can photograph bugles and star mode
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Re: More Plasma
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.
- Rich Feldman
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Re: More Plasma
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.
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.
All models are wrong; some models are useful. -- George Box
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Re: More Plasma
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.Rich Feldman wrote: Pump sound and plasma appearance are the only gauge you need at the present level of leakage.
Thank you for your advice, I will update my to do list accordingly.
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Re: More Plasma
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.
- Richard Hull
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Re: More Plasma
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
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
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
- Rich Feldman
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Re: More Plasma
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.
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.
All models are wrong; some models are useful. -- George Box
- Richard Hull
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Re: More Plasma
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
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
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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- Joined: Fri Sep 02, 2016 2:35 pm
- Real name: John Beutz
- Location: Minnesota
Re: More Plasma
Update on this afternoon's progress:
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:
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
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.
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.Richard Hull wrote:A $5.00 ball valve in the line would do the trick.
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:
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.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!
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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- Posts: 52
- Joined: Fri Sep 02, 2016 2:35 pm
- Real name: John Beutz
- Location: Minnesota
Re: More Plasma
Another update, my new KF50 cross, tee and centering rings arrived. Clamps, blanks, and maybe a digital or thermocouple gauge are on the way.