What the heck causes this flickering instability? Some days, when I turn the fusor on, I have a nice stable plasma. When the pressure gets down to 10 microns on my gauge, things start to get hairy. The current falls to near zero and then the poissor then flickers on and off. This has been driving me crazy since the day I first turned my fusor on. There is zero control when it happens, and it makes a ton of RF noise that drives all the TV's, computers and neuron counters crazy when it occurs. Fiddling with the voltage knob only increases or decreases the flickering rate.
Whatever star mode there was completely disappears, and the poissor reverts to the bugle jet structure common only at higher pressures. Remember, the pressure is 6 microns at this point.
Normally, when I do fusion, it is at pressures of 15-19 microns according to my gauge. There is always a well-defined star and there is full control over the voltage and current, which is usually up around 20kV and 12mA. Extinction occurs at 10 microns, always.
Now, if the system starts up in "flicker mode," extinction occurs at 2 microns, and there is no star, ever. If I raise the pressure to 15 microns as I would normally do for fusion, there is no star or fusion. Rather, there is a poissor with a bugle jet, and the system goes into current limit mode. The voltage at this point is only 5kV and I have no control over the current, which is usually 25mA. When the system flickers, the maximum allowed voltage is 18kV @ 2mA.
The first time I had this problem, I had to rip the fusor apart completely and install a new grid. This solved the problem for about 4 weeks until that grid finally bit the dust and needed to be replaced.
If I sit there for two hours and rig up a complex jungle gym of magnets on the surface of the chamber, then I can get the system to revert to the stable fusion mode of operation I described above. The stability is only temporary though, lasting anywhere from 5 minutes to an hour based on reasons unknown to me.
So it appears there are two completely different regimes of operation. I am at a loss when it comes to explaining why this is going on. The insulators are brand new and clean, the grid has been removed of any sharp or protruding edges, and the power supply is a high quality 1kW switchmode supply from glassman. It is not arcing, as the current draw is next to nothing. The system has been sealed for months and never been allowed to be open to the atmosphere, so it is not contaminants.
The only thing I can think of is that there just isn't enough ionization going on. Would the solution be to just retire this power supply and raise my volatge over the 20kV to which I am currenlt limited?
Endless Confusion and other observations
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Brian McDermott
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Adam Szendrey
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Re: Endless Confusion and other observations
Or, try installing thermionic cathodes, for increased ionization at lower pressures, that might stabilize your system.
Adam
Adam
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Brian McDermott
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Re: Endless Confusion and other observations
I had thought of that, but that would require almost a month of down time to acquire two more power supplies (one for the 3rd grid and one for the filament), another feedthrough, and a lot of tungsten wire which I do not currently have (unless Nichrome can be used as a cheap and dirty substitute). I don't think I'm ready for a thermionic system yet.
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Richard Hull
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Re: Endless Confusion and other observations
All this is very old and is just a function of ionized gases.
All fusioneers note this effect. Plasma club members who have a superior vacuum steup also see it. It tells you, you have a good seal and a good pump.
The larger your capacitor in the filter of the power supply, the worse the effect is as you are making a relaxation oscillator out of the fusor, but with a huge energy reserve. This can be easily reproduced with a simple NE-2 lamp, a capacitor and resistor.
The fusor, at low pressures, develops a negative resistance characteristic and an "on-off voltage hysteresis" so common to all low pressure gas devices.
This particular subject has had many discussions in these forums over the years. To have the effect go away, for the most part, you must have NO filter capacitor in your supply. This means that to have a smooth fusor you must full wave rectify. It also means that your fusion will effectively peak at a 120hz rate though you will not detect it. (if you think about this you will know why - left as an exercise for the student)
Basically, at the extinction point, your voltage is X. Once the plasma goes away, your start foltage is X+Y. Once raised to X+Y the fusor re-ignites and the current is nearly infinite. A monsterous pulse of RF energy is the result. The capacitor buckles under the load and the voltage falls below extinction and the plasma goes out. This repeats itself if the applied, filtered voltage is high enough. You see it as "flicker". The electronics engineer sees it as a very high peak power relaxation oscillator.
As the fusor has no fixed pressure, as in an NE-2 lamp, the fusor appears to do this over a broad range of voltages. Here, the effect is, effectively, pressure related. Extinction for any device is a function of geometry, pressure and voltage. With the fusor we are constantly changin two of the variables and thus the thing seems unpredicatble, whacked out, and is a frustrating thing to adjust.
Once a SEALED fusor is under a good vacuum from many runs, you can't glow clean much any more as the pump will pull the device to extinction very quickly. When this happens it is time ot kill the voltage and let the pump do its work. Once you arrive at what you feel is the base pressure for the pump, introduce the D2 and take the fusor up to a point well above extinction. You can't fight extinction! Don't try.
Richard Hull
All fusioneers note this effect. Plasma club members who have a superior vacuum steup also see it. It tells you, you have a good seal and a good pump.
The larger your capacitor in the filter of the power supply, the worse the effect is as you are making a relaxation oscillator out of the fusor, but with a huge energy reserve. This can be easily reproduced with a simple NE-2 lamp, a capacitor and resistor.
The fusor, at low pressures, develops a negative resistance characteristic and an "on-off voltage hysteresis" so common to all low pressure gas devices.
This particular subject has had many discussions in these forums over the years. To have the effect go away, for the most part, you must have NO filter capacitor in your supply. This means that to have a smooth fusor you must full wave rectify. It also means that your fusion will effectively peak at a 120hz rate though you will not detect it. (if you think about this you will know why - left as an exercise for the student)
Basically, at the extinction point, your voltage is X. Once the plasma goes away, your start foltage is X+Y. Once raised to X+Y the fusor re-ignites and the current is nearly infinite. A monsterous pulse of RF energy is the result. The capacitor buckles under the load and the voltage falls below extinction and the plasma goes out. This repeats itself if the applied, filtered voltage is high enough. You see it as "flicker". The electronics engineer sees it as a very high peak power relaxation oscillator.
As the fusor has no fixed pressure, as in an NE-2 lamp, the fusor appears to do this over a broad range of voltages. Here, the effect is, effectively, pressure related. Extinction for any device is a function of geometry, pressure and voltage. With the fusor we are constantly changin two of the variables and thus the thing seems unpredicatble, whacked out, and is a frustrating thing to adjust.
Once a SEALED fusor is under a good vacuum from many runs, you can't glow clean much any more as the pump will pull the device to extinction very quickly. When this happens it is time ot kill the voltage and let the pump do its work. Once you arrive at what you feel is the base pressure for the pump, introduce the D2 and take the fusor up to a point well above extinction. You can't fight extinction! Don't try.
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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Brian McDermott
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Re: Endless Confusion and other observations
I'm using a switchmode supply with a CW multiplier. The only capacitors on
the DC output are the capacitors in the multiplier. I also notice that there is a
lot of audible noise in the power supply unit itself that sounds like snapping or
arcing, even though there is no evidence that either of these are occuring.
The fusor has been sealed for 3 months, glow cleaned, trapped and baked
numerous times. The pressure reaches zero on my TC gauge within 45
seconds of opening the main valve.
The flickering goes away when I apply a magnetic field to the chamber.
Why? Sometimes this solves the problem and creates a star mode, and other
times it does not. The occurance of this problem seems to have no
correlation with the cleanliness of the system.
the DC output are the capacitors in the multiplier. I also notice that there is a
lot of audible noise in the power supply unit itself that sounds like snapping or
arcing, even though there is no evidence that either of these are occuring.
The fusor has been sealed for 3 months, glow cleaned, trapped and baked
numerous times. The pressure reaches zero on my TC gauge within 45
seconds of opening the main valve.
The flickering goes away when I apply a magnetic field to the chamber.
Why? Sometimes this solves the problem and creates a star mode, and other
times it does not. The occurance of this problem seems to have no
correlation with the cleanliness of the system.
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Richard Hull
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Re: Endless Confusion and other observations
This was part of my post. A good seal and long held vacuum is a clean vacuum and extinction issues appear.
As for the magnet..............you have just rediscovered the principle of the ion pump!! A magnetic field will always curl up the electrons to improve ionization probability and efficiency in any volume. The magnet mimes an increase in pressure or voltage, all which, ionize gas at any pressure. Ion pumps work up to 10e8 or higher! How? They glow clean, but they use an intense magnetic field to force ionization in a gas that will not allow it normally.
Richard Hull
As for the magnet..............you have just rediscovered the principle of the ion pump!! A magnetic field will always curl up the electrons to improve ionization probability and efficiency in any volume. The magnet mimes an increase in pressure or voltage, all which, ionize gas at any pressure. Ion pumps work up to 10e8 or higher! How? They glow clean, but they use an intense magnetic field to force ionization in a gas that will not allow it normally.
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
Re: Endless Confusion and other observations
There's a piece of this view that bothers me somewhat But, maybe I just missed the significance of your explanation, Richard.
Gas "discharges" are in fact avalanche processes.. that require a certain number of electrons to create. The Townsend criteria for such things is that the electron avalanche has about 10^8 electrons or contains some 160 picocouombs of charge. This requires a certain number of generations of ionizations which depends on the attachment and ionization coefficiants for the gas species involved.
My problem in understanding arises from the low gas density and the apparent lack of sufficient collisions except for sporadic occurrences. The question is then: What causes these occasional pressure increases, which must be rather localized within the fusor volume? I am wondering if this is the work of secondary ionization and/or electron induced desorption of gases from the center grid structure, ( or somewhere else).? One could imagine these miscellaneous gasses being gettered or scavenged by the clean metal surfaces and then from time to time, under electron bombardment, releasing the gases as ions which would then tend to travel somewhere...in sufficient quantities to cause a current pulse. Ejected up into the fusor volume, these gases might well become neutralized and avoid the pump inlet a number of times by being adsorbed again onto another surface.
The problem with stable operation under a re-admission of D2 gas,might simply be the clean surfaces are "gettering" the first round of gas, and thus dropping the pressure, and extinguishing the discharge. Following this picture to its conclusion, a soak or flood of gas above normal operating pressures, by a few microns, and then a pumpdown to operating pressures should see the operation stabilize.
This suggests, (if reasonably correct) that one should keep the fusor under a low D2 pressure when not in use. Should be easy to check out.
Dave Cooper
Gas "discharges" are in fact avalanche processes.. that require a certain number of electrons to create. The Townsend criteria for such things is that the electron avalanche has about 10^8 electrons or contains some 160 picocouombs of charge. This requires a certain number of generations of ionizations which depends on the attachment and ionization coefficiants for the gas species involved.
My problem in understanding arises from the low gas density and the apparent lack of sufficient collisions except for sporadic occurrences. The question is then: What causes these occasional pressure increases, which must be rather localized within the fusor volume? I am wondering if this is the work of secondary ionization and/or electron induced desorption of gases from the center grid structure, ( or somewhere else).? One could imagine these miscellaneous gasses being gettered or scavenged by the clean metal surfaces and then from time to time, under electron bombardment, releasing the gases as ions which would then tend to travel somewhere...in sufficient quantities to cause a current pulse. Ejected up into the fusor volume, these gases might well become neutralized and avoid the pump inlet a number of times by being adsorbed again onto another surface.
The problem with stable operation under a re-admission of D2 gas,might simply be the clean surfaces are "gettering" the first round of gas, and thus dropping the pressure, and extinguishing the discharge. Following this picture to its conclusion, a soak or flood of gas above normal operating pressures, by a few microns, and then a pumpdown to operating pressures should see the operation stabilize.
This suggests, (if reasonably correct) that one should keep the fusor under a low D2 pressure when not in use. Should be easy to check out.
Dave Cooper
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Alex Aitken
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Re: Endless Confusion and other observations
I wonder if it would be possible to home wind an EHT inductor to prevent the flickering with DC power supplies. Or maybe putting the secondary of a neon sign transformer in series would be enough.
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Richard Hull
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Re: Endless Confusion and other observations
There can be many theories about what goes on in the pulsing fusor. The important thing is that it is normal and somewhat unavoidable even in a flowing D2 regime.
The instant plasma extinguishes there is always a rise in pressure. Every human being who has operated a well instrumented, deuterium gased fusor has seen this and it is obvious that it is desorption.
Every Farnsworth team member, in separate interviews, noted this to me and recognized that I was a true fusioneer when I also concurred. Hydrogen burys itself in all metals rather easily at any pressure. Force it in by ion bombardment or high speed neutral collision that is uniform, constant and unrelenting as in the 300 watt plus environment of a fusor and the instant your plasma energy ceases........YOU WILL GET A PUFF OF GAS. This is as common as the sea sickness and you can't make it go away.
There are a lot of issues that can cause a fusor to pulse, extinguish, reignite, etc. Only a few are easily controlled. That is about the best one can do. The plasma is a smooth and continuous pump for D2 into large surface areas..... When it goes away, the osmotic pressure to retain the hydrogen surface gas load also goes away and you get the pressure pulse or spike as Gene Meeks calls it.
Richard Hull
The instant plasma extinguishes there is always a rise in pressure. Every human being who has operated a well instrumented, deuterium gased fusor has seen this and it is obvious that it is desorption.
Every Farnsworth team member, in separate interviews, noted this to me and recognized that I was a true fusioneer when I also concurred. Hydrogen burys itself in all metals rather easily at any pressure. Force it in by ion bombardment or high speed neutral collision that is uniform, constant and unrelenting as in the 300 watt plus environment of a fusor and the instant your plasma energy ceases........YOU WILL GET A PUFF OF GAS. This is as common as the sea sickness and you can't make it go away.
There are a lot of issues that can cause a fusor to pulse, extinguish, reignite, etc. Only a few are easily controlled. That is about the best one can do. The plasma is a smooth and continuous pump for D2 into large surface areas..... When it goes away, the osmotic pressure to retain the hydrogen surface gas load also goes away and you get the pressure pulse or spike as Gene Meeks calls 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
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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Jon Rosenstiel
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Re: Endless Confusion and other observations
Question about your grid. What type of wire?
Jon Rosenstiel
Jon Rosenstiel
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Brian McDermott
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Re: Endless Confusion and other observations
The grid is made from 304 stainless steel.
Re: Endless Confusion and other observations
Brian,
I would be very interested to hear if you found out the cause of the arcing noise from your psu.
Henry and I have been experiencing a very similar problem, we were having no end of problems with interference and even once we stripped our system right down to basics we still didn’t find the cause. We did however notice a quiet arcing sound coming from somewhere which coincides with and interference we get. We have looked for hours to find the source of this noise with no success. Obviously it’s outside the chamber somewhere, and it isn’t simply due to any oscillation effects due to the fusor as it still occurs when our chamber is vac'd down to zero. Our psu is a regular xray tranny one, no silicon to complicate things
The only other thing we noticed is that our output resistor on the pot div has lost about 15k since its installation, and we have killed two meters on it. We have replaced this but have yet to check whether we still get arcing.
We've been frantically getting ready, trying to eliminate any bugs last weekend as our deuterium is coming this morning, so hopefully we will be fusioneers by the afternoon!!
Cheers,
Fergus.
I would be very interested to hear if you found out the cause of the arcing noise from your psu.
Henry and I have been experiencing a very similar problem, we were having no end of problems with interference and even once we stripped our system right down to basics we still didn’t find the cause. We did however notice a quiet arcing sound coming from somewhere which coincides with and interference we get. We have looked for hours to find the source of this noise with no success. Obviously it’s outside the chamber somewhere, and it isn’t simply due to any oscillation effects due to the fusor as it still occurs when our chamber is vac'd down to zero. Our psu is a regular xray tranny one, no silicon to complicate things
The only other thing we noticed is that our output resistor on the pot div has lost about 15k since its installation, and we have killed two meters on it. We have replaced this but have yet to check whether we still get arcing.
We've been frantically getting ready, trying to eliminate any bugs last weekend as our deuterium is coming this morning, so hopefully we will be fusioneers by the afternoon!!
Cheers,
Fergus.
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Brian McDermott
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Re: Endless Confusion and other observations
You may have a completely different problem. I took a look at my system yesterday and found that the grid was misaligned by nearly its full radius. I pulled it forward a bit and the problem went away. I still get some flashing, but there is no noise associated with it.
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Frank Sanns
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Re: Endless Confusion and other observations
Fergus,
I am sure you checked all of your electrical connections but check them again. At 50 microns, a connection only has to be close to be working. Just a few volts and connection is made. Take a wire cold soldered to another wire or loosesly connected to another element. It will behave just like a good circuit. As the pressures get down and the voltages start to rise, there is not enough air or deuteium to carry the current and you end up with a sporatic insulator. Check the connections, (or maybe you have a faulty ballast resistor). The other reason that leads me to believe it is a connection is that you are getting high RFI. Th is the number one reason for RFI in a circuit is poor connections. These things can turn any length of wire in to a radiating antenna. ALL connections need to be snug and no mixing of metals so that galvanic action builds up a insulative layer between electrical parts. I know from my fusor, that if my inner gridd is not wound tight enough, it will light and extinguish and give tons of RF noise and the like.
Frank S.
I am sure you checked all of your electrical connections but check them again. At 50 microns, a connection only has to be close to be working. Just a few volts and connection is made. Take a wire cold soldered to another wire or loosesly connected to another element. It will behave just like a good circuit. As the pressures get down and the voltages start to rise, there is not enough air or deuteium to carry the current and you end up with a sporatic insulator. Check the connections, (or maybe you have a faulty ballast resistor). The other reason that leads me to believe it is a connection is that you are getting high RFI. Th is the number one reason for RFI in a circuit is poor connections. These things can turn any length of wire in to a radiating antenna. ALL connections need to be snug and no mixing of metals so that galvanic action builds up a insulative layer between electrical parts. I know from my fusor, that if my inner gridd is not wound tight enough, it will light and extinguish and give tons of RF noise and the like.
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS