Anomaly in demo fusor.
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Anomaly in demo fusor.
A strange anomaly recently popped up in my demo fusor. In the upper right corner of the chamber a small but bright and well defined cloud of plasma can be seen while the demo is running. I think it is related to my power supply. A few days ago my neon sign transformer died and as I am entering this in the evergreen state fair and I needed to get it judged I did not have time to get a new one. So I threw together a power supply using a flyback transformer and a 3055 driving circuit. With the neon sign transformer I never saw anything like this, but ever since I hooked the flyback up this has appeared every time I have turned the demo on. I have included a few pictures from various angles. Anyone have any idea what that is?
P.S. Could someone add me to the plasma club
EDIT: The original links didn't work, so I put some new ones in.
<a href="http://s1234.photobucket.com/albums/ff4 ... G_5190.jpg" target="_blank"><img src="http://i1234.photobucket.com/albums/ff4 ... G_5190.jpg" border="0" alt="Photobucket"></a>
<a href="http://s1234.photobucket.com/albums/ff4 ... G_5188.jpg" target="_blank"><img src="http://i1234.photobucket.com/albums/ff4 ... G_5188.jpg" border="0" alt="Photobucket"></a>
<a href="http://s1234.photobucket.com/albums/ff4 ... G_5187.jpg" target="_blank"><img src="http://i1234.photobucket.com/albums/ff4 ... G_5187.jpg" border="0" alt="Photobucket"></a>
P.S. Could someone add me to the plasma club
EDIT: The original links didn't work, so I put some new ones in.
<a href="http://s1234.photobucket.com/albums/ff4 ... G_5190.jpg" target="_blank"><img src="http://i1234.photobucket.com/albums/ff4 ... G_5190.jpg" border="0" alt="Photobucket"></a>
<a href="http://s1234.photobucket.com/albums/ff4 ... G_5188.jpg" target="_blank"><img src="http://i1234.photobucket.com/albums/ff4 ... G_5188.jpg" border="0" alt="Photobucket"></a>
<a href="http://s1234.photobucket.com/albums/ff4 ... G_5187.jpg" target="_blank"><img src="http://i1234.photobucket.com/albums/ff4 ... G_5187.jpg" border="0" alt="Photobucket"></a>
Re: Anomaly in demo fusor.
Links are broken
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But now that you're here, go ahead and search through the billions of photos, images and videos on Photobucket.
Steve
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But now that you're here, go ahead and search through the billions of photos, images and videos on Photobucket.
Steve
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Re: Anomaly in demo fusor.
Dang, I thought I had figured out how to embed photos. Let me see If I can fix it.
- Mike Veldman
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Re: Anomaly in demo fusor.
What is located at that point on the outer wall? The glow looks like what I'd seen as back streaming oil vapor around the vacuum port. I've also seen that glow on dissimilar metals and sometimes silver soldered joints inside a chamber. Just a couple of early morning thoughts.
mike
mike
I tried to contain myself, but I escaped.
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Re: Anomaly in demo fusor.
I have seen that in my chamber where there was a leak. The high pressure gas jet coming in the pinhole leak seemed to increase the quantity of ionization in the area.
- Doug Coulter
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Re: Anomaly in demo fusor.
I've seen this kind of thing many times while pumping down. You need to get to lower pressure.
Why guess when you can know? Measure!
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Re: Anomaly in demo fusor.
Hello,
for me this looks like a perfectly normal, poor-vacuum-discharge. With decreasing pressure it will disappear.
http://img809.imageshack.us/img809/6360/p2090063.jpg
http://img560.imageshack.us/img560/2230/p2020132.jpg
Adrian
for me this looks like a perfectly normal, poor-vacuum-discharge. With decreasing pressure it will disappear.
http://img809.imageshack.us/img809/6360/p2090063.jpg
http://img560.imageshack.us/img560/2230/p2020132.jpg
Adrian
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Re: Anomaly in demo fusor.
Nothing is located their. No weld of any sort, no port, nothing.
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Re: Anomaly in demo fusor.
Could it be that you have reversed the polarity with your new flyback supply?
TV flybacks produce positive high voltage while the fusor's hollow cathode needs a negative voltage.
What you see is a stable blob of plasma, which self-assembles under the right conditions:
https://crppwww.epfl.ch/~duval/P2_003.pdf
TV flybacks produce positive high voltage while the fusor's hollow cathode needs a negative voltage.
What you see is a stable blob of plasma, which self-assembles under the right conditions:
https://crppwww.epfl.ch/~duval/P2_003.pdf
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Re: Anomaly in demo fusor.
I don't think so. I am pulling my voltage off the ground pin of the flyback due to exactly that reason. Maybe the flyback produces a small amount of positive voltage on the ground pin?
Re: Anomaly in demo fusor.
Chris O' -
My initial thought is similiar to other's here... it probably is pressure related... a tiny leak, outgassing, a bit of contaminant (grease, fingreprint, etc.) or just a place where the ionization is favored at the average chamber pressure.
Try to lower the pressure, if you can.
Dave Cooper
My initial thought is similiar to other's here... it probably is pressure related... a tiny leak, outgassing, a bit of contaminant (grease, fingreprint, etc.) or just a place where the ionization is favored at the average chamber pressure.
Try to lower the pressure, if you can.
Dave Cooper
- Doug Coulter
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Re: Anomaly in demo fusor.
He mentioned an NST supply. What I see here with DC is that the color of the wall spot I see when the pressure is "way too high" is a different color -- brown, than what you see as the cathode glow on the grid (same as he pictured). If he tried DC, he might see that too, and that would confirm. For whatever reason, you get the two color thing with DC but can't see it with AC, something weird about what states of nitrogen make what spectral lines the most efficiently, I believe.
When I do this in my systems, and everything is nicely symmetric, I see the wall spot race around the tank walls as it pumps down. It's a nice show. If it sits on one spot, I know I don't have my grid centered.
When I do this in my systems, and everything is nicely symmetric, I see the wall spot race around the tank walls as it pumps down. It's a nice show. If it sits on one spot, I know I don't have my grid centered.
Why guess when you can know? Measure!
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Re: Anomaly in demo fusor.
Excuse me, but Dueg I was unable to understand your post. Is their a missing reply? Whats all this about different colored plasma? And I get the impression that you think I am using AC: In reality I have always been using DC. The neon sign transformer was rectified and the fly back transformer is internally rectified. Could you repost with clearer wording?
- Doug Coulter
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Re: Anomaly in demo fusor.
Sorry 'bout that.
I have noticed, when running a discharge during pumpdown, with air as the main thing in the tank, that the glow spot I'll often see on the outer wall is a different color (brownish) than the glow on the grid, which tends to be bluish-purple or pinky-blue (same as you show). This is with DC, grid negative. This seems to be something you get with nitrogen, as some gas-jet-type ion sources I've built also showed those colors at different points in the de-excitation of the nitrogen as the jet evolved over time (distance from the jet and electrical field origin).
There are some movies of what the fusor looks like with different gas pressures on my youtube channel, but I don't happen to have one that shows this effect, it's usually pretty fleeting with fast pumps, which is what I've got here.
http://www.youtube.com/user/DCFusor
(youtube only shows a few of the more recent ones unless you click "show all")
If you'd like, I can make a movie of it happening here -- saw it again just the other day after a teardown of my smaller fusor, it should be easy to do again. Very pretty and it impresses those who don't understand you can't get near to fusion at any pressure even close to that high. That's where you are at now -- far too high pressure even for a good demo fusor. Either you have a leak or a bad pump, as a 2 stage mech pump alone will almost get you to the point of "putting out the lights" in a tight system with some patience.
In the meanwhile, here's a couple that show pumpdowns, starting from a lower pressure than where the wall-spots exist. Not very good videography here, I was just learning how to do it.
http://www.youtube.com/user/DCFusor#p/u/5/Sb3x2yPFcB8
http://www.youtube.com/user/DCFusor#p/u/6/sY_jKJQUAlg
From what I've seen -- you're just at much too high a pressure to see what I'm seeing in the movies above -- I see the wall spots at about double-triple the pressure I started from in those movies- you're at several (at least) millibars, about factor 100 higher than where we run fusion. When I call out pressures, they're all in millibars as that's what my gages speak, and are the gage readings, uncorrected for the known errors due to gas type. This works for me as it's repeatable so I don't really care what the actual true pressure is, just that I can hit the good number over and over reliably.
After a pretty short experience with it, the appearance of discharge itself along with the power supply numbers tells you more than the gas gage's limited resolution can anyway. Once you tune your color sense, you can also tell quite a bit about any impurities in the gas as well. A pocket spectroscope is a handy accessory for that -- the poor man's mass spectrometer, a trick mentioned in John Strong's book.
I have noticed, when running a discharge during pumpdown, with air as the main thing in the tank, that the glow spot I'll often see on the outer wall is a different color (brownish) than the glow on the grid, which tends to be bluish-purple or pinky-blue (same as you show). This is with DC, grid negative. This seems to be something you get with nitrogen, as some gas-jet-type ion sources I've built also showed those colors at different points in the de-excitation of the nitrogen as the jet evolved over time (distance from the jet and electrical field origin).
There are some movies of what the fusor looks like with different gas pressures on my youtube channel, but I don't happen to have one that shows this effect, it's usually pretty fleeting with fast pumps, which is what I've got here.
http://www.youtube.com/user/DCFusor
(youtube only shows a few of the more recent ones unless you click "show all")
If you'd like, I can make a movie of it happening here -- saw it again just the other day after a teardown of my smaller fusor, it should be easy to do again. Very pretty and it impresses those who don't understand you can't get near to fusion at any pressure even close to that high. That's where you are at now -- far too high pressure even for a good demo fusor. Either you have a leak or a bad pump, as a 2 stage mech pump alone will almost get you to the point of "putting out the lights" in a tight system with some patience.
In the meanwhile, here's a couple that show pumpdowns, starting from a lower pressure than where the wall-spots exist. Not very good videography here, I was just learning how to do it.
http://www.youtube.com/user/DCFusor#p/u/5/Sb3x2yPFcB8
http://www.youtube.com/user/DCFusor#p/u/6/sY_jKJQUAlg
From what I've seen -- you're just at much too high a pressure to see what I'm seeing in the movies above -- I see the wall spots at about double-triple the pressure I started from in those movies- you're at several (at least) millibars, about factor 100 higher than where we run fusion. When I call out pressures, they're all in millibars as that's what my gages speak, and are the gage readings, uncorrected for the known errors due to gas type. This works for me as it's repeatable so I don't really care what the actual true pressure is, just that I can hit the good number over and over reliably.
After a pretty short experience with it, the appearance of discharge itself along with the power supply numbers tells you more than the gas gage's limited resolution can anyway. Once you tune your color sense, you can also tell quite a bit about any impurities in the gas as well. A pocket spectroscope is a handy accessory for that -- the poor man's mass spectrometer, a trick mentioned in John Strong's book.
Why guess when you can know? Measure!
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Re: Anomaly in demo fusor.
Thanks. That was much clearer.
I believe the anomaly is probably a leak as it takes a very short amount of time (about an hour) for the demo to get back to atmospheric pressure. This is in comparison to before when I was able to get it to hold a vacuum for days. Before I was also able to get a nicely defined plasma ball. unfortunately., I have no time to fix it, as the demo is going to fair today. Thanks for your help everyone.
By the way, how do I go about plugging leaks such as this.
I believe the anomaly is probably a leak as it takes a very short amount of time (about an hour) for the demo to get back to atmospheric pressure. This is in comparison to before when I was able to get it to hold a vacuum for days. Before I was also able to get a nicely defined plasma ball. unfortunately., I have no time to fix it, as the demo is going to fair today. Thanks for your help everyone.
By the way, how do I go about plugging leaks such as this.
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Re: Anomaly in demo fusor.
I agree with Wilfried Heil. It looks much like my glow discharge with positive current to the (anode) grid.
It doesn't matter so much which lead you hook up, what matters is the diode arrangement with that lead.
If you normally have the hot lead to the 'cathode' grid, and here you maintained the diode arrangement but hooked up the 'ground' lead while grounding the fusor case to the normal cathode lead, you have reversed the current feed- ie-a pos anode grid.
There is also probably some anomulous glow discharge due to pressure, sharp projections.
Dan Tibbets
It doesn't matter so much which lead you hook up, what matters is the diode arrangement with that lead.
If you normally have the hot lead to the 'cathode' grid, and here you maintained the diode arrangement but hooked up the 'ground' lead while grounding the fusor case to the normal cathode lead, you have reversed the current feed- ie-a pos anode grid.
There is also probably some anomulous glow discharge due to pressure, sharp projections.
Dan Tibbets