Alexey's fusor progress

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Alexey Khrushchev
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Joined: Thu Jul 06, 2023 3:36 am
Real name: Alexey Khrushchev
Location: Moscow

Re: Alexey's fusor progress

Post by Alexey Khrushchev »

If the problem is gas contamination, I don't know how to fix it. I get the deuterium in a PEM cell, then the gas goes through a silica gel cartridge (with color indication) to remove water. The gas is then bubbled through vacuum oil over a layer of granular KOH. Should I install an activated carbon cartridge to remove traces of oil?

Yeah, I noticed by the way that the color of the plasma has turned blue lately, without the red tint like it used to be.
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Dennis P Brown
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Real name: Dennis Brown

Re: Alexey's fusor progress

Post by Dennis P Brown »

No expert but I think your deuterium is fine (red or blue is typical for deuterium discharge color.) I would avoid bubbling through oil or KOH; no real need. Some here don't bother to dry their PEM cell D2 either.
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Liam David
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Location: PPPL

Re: Alexey's fusor progress

Post by Liam David »

The arc that you're describing is absolutely caused by some kind of field enhancement, and in your case the triple junction is to blame. The path from triple junction to ground is across the flat glass surface and surfaces have lower breakdown thresholds than volumes.

I don't have enough experience with PEM cell deuterium to really comment on its purity (I use bottled gas only), but it may not be the gas itself that is to blame. Consider, for example, the adsorbed gases on the surface of your stalk and cathode. Under plasma bombardment, that gas will be driven off which will locally enhance ionization and thus a positive feedback loop forms. Locally, the current density becomes large and you see a brief arc. This is one of the reasons conditioning is important. Running a lower-energy plasma helps remove this gas, which corroborates Dennis' explanation of his system misbehaving unless brought up slowly. In fact, this is the main issue plaguing my system, especially with my cathode design.
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Rich Gorski
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Re: Alexey's fusor progress

Post by Rich Gorski »

Alexey,

I agree with Dennis and Liam on this arcing issue. It may be worth redesigning your HV feedthrough to increase the surface path length along the glass. Maybe look at a commercial HV feedthrough like from K Lester vacuum to get a look at their proven design. They have one that claims to handle 100kV.

Good luck,
Rich G.
Alexey Khrushchev
Posts: 118
Joined: Thu Jul 06, 2023 3:36 am
Real name: Alexey Khrushchev
Location: Moscow

Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Thank you all for the discussion!

Vacuum oil is the working fluid of my gas storage system. It is an inverted dividing funnel that is placed in a wide vial. Initially the funnel is filled with oil and when I feed deuterium the oil is forced out of the funnel into the vial. In this way I can store up to 125ml of pure deuterium. Underneath the oil layer are KOH pellets to remove traces of water.

I agree that the breakdowns are a consequence of having a triple point, but I can't find a professional insulator at the moment.

I always burn the chamber before working, for this I increase the pressure to 50 microns and set the current to 20-30 mA, the cathode is white hot. I think all adsorbed gases fly out of the chamber as a result of this procedure.

If it is not the purity of the deuterium, why do breakdowns occur at high gas flow rates? Again, at 1 ml/min and 20 micron pressure, the plasma is stable, but at 10 ml/min and 20 micron pressure, there is no plasma, and when I try to increase the voltage, breakdown occurs.
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