Fusor Initial Operation

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Dennis P Brown
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Fusor Initial Operation

Post by Dennis P Brown »

The new window/electrode feed thru is in and I ran the unit to season it with deuterium. While that worked and I did get a bit more stable system - that is, I was able, after an hour or so of seasoning to get 22 kV at 38 ma with that current rock steady ( a rather high power - over 800 watts); however, the pressure during that two minute run was an unknown due to the plasma leaking through the screen that covers the TC gauge (likely the higher voltage causes this issue.) The reading on the TC varied over nearly the entire range of its display including atm during that run; I know those readings are not physical because the current did remain steady as did the plasma glow - not possible if the pressure changes even by just two or three microns.

An issue that puzzles me is why I can't get a stable run in the high end of my voltage range - more on this after some details on what is related to this problem.

During most all the runs the diffusion pump has a strange noise that occurs once every minute or so and the vacuum will suddenly fall 5 or more microns (depending on the starting pressure in the 10 - 20 range.) I am lost as to what could cause this odd behavior/sound - the sound is not unlike balled up aluminum foil being crushed or a slight metallic rattling sound. Maybe the oil level is wrong? (Too high or too low? Of course, no way to determine that without removing the DP and pouring out the oil to measure the volume. That would be an extreme pain.)

The sudden noise can't be water vapor or organic contaminates out gassing because I get a large pressure drop just after the sound - the exact opposite of what would occur with out gassing from the hot oil. This problem and sound also occurs at high vacuum (no deuterium feed) - that is, at 7 * 10^-5 torr I will get the temporary sound and the pressure will quickly drop to 2 * 10 ^-5 torr. Then slowly creep up due to chamber wall out gassing (the system has been open to the air for a number of months.)

For now I will add a second metal screen at the base of the chamber to further protect the TC.

For all runs I do establish a base pressure of 10-15 microns of deuterium gas but the system then oscillates between 5 to 20 microns (no plasma!) due to the effect of outflow caused by the varying performance of the DP - the D2 inflow is at a constant feed rate using a many turn micro-needle valve so doubt that is an issue. For plasma runs, as the current goes up so does the out gassing so that is a separate issue (but one that will surely get better as I further season the chamber and the special silver epoxy for the electrode/ceramic mount better cures during heat cycling.)

This problem is rather aggravating since it generally prevents me from achieving a steady current and especially prevents me from getting my voltage above 22 kV - when the pressure is correct for operating the voltage in the 26-30 kV range (the conductivity of the gas) the pressure then always swings a great deal - first suddenly dropping then rapidly rising as D2 continues to enter the system (so at the higher voltage my current will then rapidly go off scale high (over 60 ma and then (after I lower the current to under 60) fall to zero.) Any ideas relative to the pressure fluctuations and the DP sounds would be appreciated.
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Dennis P Brown
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Re: Fusor Initial Operation

Post by Dennis P Brown »

Quick up date; the second metal screen in my fusor chamber works and the TC reads well and is stable even with high current/voltage plasma's now. I was lucky the TC is installed below the throat of the larger chamber allowing an easy fix.

I did get a stable plasma (after a lot of bad runs) at 26 kV and 35 mill-amps for 2 - 3 minutes at 6 microns. (The TC is fairly accurate since I did do a calibration a while ago with an accurate gauge.)

That specific run led to my realizing that the electrode I made gets too hot and causes the epoxy that binds the copper rod to ceramic to out gas - I now know this for two reasons: first, the pressure in that stable system started to suddenly rapidly rise: so that wasn't chamber wall out gassing; and second, I can see burned contaminates all around the electrode area.

I still had the noise issue and sudden and very rapid fall of the chamber pressure but I did manage a work-around. This problem may be a serious issue that returns but as I discovered (no surprise here) I have a far more significant problem to now solve.

On the bright side that level of energy and power, I would think, should be sufficient to produce measurable neutrons if I had a detector.

I may try water cooling the ceramic section of the electrode. That isn't ideal nor terribly safe so I will weigh my options first before trying that idea. Forced air cooling would be safer but is far more involved to do - really, how to add cooling fins that are effective?

If I solve this electrode problem, guess like Steve and his post today, my next job is to work on the neutron measurement issue.
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Dennis P Brown
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Re: Fusor Initial Operation

Post by Dennis P Brown »

Well, had to forgo HEAS due to a family issue; at least I got to make some good progress on my fusor.

The system is fairly stable now and runs well at any current I desire at its maximum voltage of 31 kV (power is from 600 to over a 1000 watts!). I tend to operate between 25 to 35 milli-amps to keep the x-former cool - it has a large fan to keep heat build up to a minimum. I have some images of the system running at max voltage. I ran the system for a minute at 40 -50 milli-amps (& max voltage) and the electrode went to white heat, but the upper assembly remained cool. This is a rather important "fix" for my system since over heating of the electrode cause its binder to out gas (leading to pressure variation issues) but far worse, if that section gets too hot, then it can fail completely (the fusor would be open to the air!)

The over heating issue has been addressed by using a fan for forced air cooling on a large metal mesh (a high current metal strap.) Even as the electrode is glowing white hot, the electrode upper assembly now stays cool to the touch (I touch this only after all HV is shut down!) See the photo of the electrode fan cooling system. I use non-conducting thermally conductive paste to improve cooling between the ceramic and metal mesh.

I am rather pleased with the systems performance. Once I set the voltage, my current is easy to adjust using my deuterium micro-valve feed. Very small changes up or down - a division or so on the scale - changes the current in the plasma. The response is instantaneous, which rather surprised me. The base pressure of 7 microns (which isn't necessarily the real pressure but is certainly close) but is consistent for my current setup allows me to obtain 31 kV with a current between 20 - 40 milli-amps. Fine adjustments sets the exact current.

The system runs at a fixed current for up to a minute before slowly drifting (some out gassing may still be an issue); I can easily control the random pressure variation that does occur with small D2 flow adjustments.

My system appears fairly seasoned now; I keep it under vacuum and re-pump it every day (mechanical only.) When I do fire up the DP it gets to the low 10^-5 torr in under ten minutes.

I guess I am done with this system until I get a neutron detector - may play with it a few more times but little point to run it; I wasn't going to get a neutron detector until I obtained a stable, useful fusor that could run at a voltage and current (power) that could reasonably guarantee I could obtain neutrons.

Guess now I will look at a He-3 tube since I have a fairly good quality adjustable high voltage power supply/pre-amp/counter system that can run either Geiger or scintillation tubes so I'd think a He-3 tube would work well with this system.

Aside: apparently, once leaks (virtual or heat induced out gassing) are done away with a fusor is more stable than I had imagined. Fair easier to operate, too.

Not that getting neutrons is so easy since that is still Terra incognita for me, for now.

One aspect that is satisfying is that as problems developed that set me back, I managed to over come them using both techniques/advice found from here, as well unique solutions I arrived at using stuff I had on hand. Now for the real battle ... neutrons (?)
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The electrode red hot and the star mode can be seen (deuterium gas)
The electrode red hot and the star mode can be seen (deuterium gas)
The upper electrode fan/mesh cooling system
The upper electrode fan/mesh cooling system
The HV power supply system - displaying 31 kV and 35 milli-amps
The HV power supply system - displaying 31 kV and 35 milli-amps
Close up of the HV gauges- lower current (normal max without an extra fan for the x-former.)
Close up of the HV gauges- lower current (normal max without an extra fan for the x-former.)
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Richard Hull
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Re: Fusor Initial Operation

Post by Richard Hull »

Looks very good. You should have no trouble doing fusion from what I see.

Sorry you couldn't make HEAS. It was a perfect day here, no rain, fabulous flamarket and record making run on fusor IV Friday evening during the pre-HEAS get together.

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 Initial Operation

Post by Dennis P Brown »

Thank you Richard. And I really regret I had to miss that flea market! I bet their were a lot of nice items!

This fusor want-a-be still lacks a neutron detector and that will be my next goal; any suggestions or ideas are appreciated. But my main goal is not to demonstrate fusion in a fusor (but yes, that is important!) but to do more accurate detection for another experiment. One is a fun idea to cause neutron emission using Pd under extreme temps (via collapse) and the second goal is to look into a new type of detector for neutron work.

So, what I am seeking is a detector that will, of course, demonstrate fusion in a fusor. Also, the detector must be fairly reliable device that is fairly sensitive but not a new project in of itself. I have a fairly high end voltage source/pre-amp system (Spectech ST360) so the detector tube type is the issue. He-3 looks the best candidate but I know some have had success with the Russian tubes.

I am including a picture of the mirror I added to the fusor so I can better avoid any minor x-ray exposure. I can also add a shield but the x-ray threat at this 30 kV level isn't likely very high. The steel walls of the chamber and the glass window is rather thick so these should be enough; maybe add some extra shielding for something to do as I look into detectors. Projects are, by definition: projects! And that means doing something with them because ... you can!
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Dennis P Brown
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Re: Fusor Initial Operation

Post by Dennis P Brown »

Quick update; decided to increase the length of the existing electrode by machining an extension rod and ceramic section. Installed these on the original electrode and pumped out the system; including another main chamber bake out. After cooling, the chamber's diffusion pump (DP) got the chamber to 1.2 * 10^-5 torr; in a full system test, the plasma ran at 31 kV and with a 3.2 microns deuterium pressure. These voltages/pressure holds very steady - a nice change! Also, I can set any current I desire from 10 to 60 milli-amps continuous without any issue. Just have to make tiny changes in the deuterium valve for a fixed voltage.

So, a few low runs (with plasma at the 2 - 3 micron range) and repeated bake outs really does appear to make the system more stable.

Looks like my pressure is now in line with what Richard generally obtains. Also, the DP is far more quite but will, on occasions, make the rattling sound and the pressure drops a bit (strange.)
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