Theoretical Question Regarding Fusor....

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Matthew Kwak
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Real name: Matthew Kwak

Theoretical Question Regarding Fusor....

Post by Matthew Kwak »

Hello, I have been building a new Fusor, with better vacuum system and an upgraded HV electrical grid, and I noticed a phenomenon that was present in my past (first) Fusor but was much more noticeable and prevalent in the new one....

Image

Image

This 'phenomenon' was..
1) The small 'clumps' of light that were appearing on the outer grid, specifically on the intersection between metal rings, and
2) Streams of light connecting outer and inner grid. The location changed on every operation....

If somebody could explain these phenomenon in theoretical aspect, regarding plasma, it would be extremely helpful...

Thank you!

P.S) Also, is the temperature of the grids related to a Fusor's operation in some way? Like, changes in resistance and voltage? The phenomenon seemed to decrease after prolonged state of usage... and I thought the only changing factor was T. of the grids...
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Dennis P Brown
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Re: Theoretical Question Regarding Fusor....

Post by Dennis P Brown »

No experience with and almost as little knowledge of fusor operation but from the picture, it looks as if you are creating arc's/plasma from where the wires are joined; as such, my guess is the braze or some flux remaining is being emitted/out gassed from the solder causing the arching/plasma "balls". Also, any sharp edges or spikes created on/by the solder can cause some concentrated glow. The decrease in the effect is consistent with what I am proposing. As for resistance in wires due to temperature, yes that can cause local increases in the wire's resistance helping to heat the local section causing more diffusion from the joint/solder leading to an increase in local plasma due an increase in the contamination ions around that section; again, my best guess - others may have better ideas.

If that is the issue, time should help correct the problem (consider changing your flux/braze.) Consider using steel wool to smooth/polish the wire joints (might help) followed by a good organic cleaning. Could also be caused by poor connection between wires leading to hot spots, which then results in some local sputtering (production in metal vapor (really; the spell check uses the english spelling for this word?))
RealBorg
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Re: Theoretical Question Regarding Fusor....

Post by RealBorg »

Looks like your grid is not as smooth as it is supposed to be. I suggest you use fine sanding paper.

Tom
Matthew Kwak
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Re: Theoretical Question Regarding Fusor....

Post by Matthew Kwak »

So the slight discrepancies in the distance between outer and inner grid could be the cause of those 'clumps'?

Um... what does 'contamination' mean here? And how does plasma form in such areas specially? Could it be concentrated charges in sharp location, resulting an increase in electron collision? And, what is the 'streaming' of light, or plasma (uncertain) between the two grids? Sometimes that 'stream' becomes a 'plane(as in, geometry)' which shows a wave pattern of high frequency.... i do not have a video of that phenomenon, because it is rare and doesn't last long...

I have read about something called Langmuir Wave - could this be something related to it? The description in the book did sound a bit similar..

Forgive me for my lack of knowledge! :( But I want to learn.
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Liam David
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Re: Theoretical Question Regarding Fusor....

Post by Liam David »

By contamination we mean oil, dust, dirt, etc... (Fingerprints should also be thought of as contaminants). Inner and outer grids are usually dipped in acetone or alcohol to remove these impurities. You did mention the phenomenon faded after a while, leading me to believe that the bright spots are impurities and contaminants burning off.
-Liam David
prestonbarrows
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Re: Theoretical Question Regarding Fusor....

Post by prestonbarrows »

Surface interactions in a plasma are generally quite complex. The background pressure, local electric field, presence of surface contaminates and surface micro-structure all can have large effects. In a home brew system like this, none of these parameters are going to be extremely well controlled.

In general though, looks to be concentrated at joints with sharper points which will have the highest local electric fields. Any oils or dust or hair or scratches will cause similar discharges. Over time, there is a negative feedback effect as these points get sputtered away faster by ion impacts.

If you really want to get into it, Principles of Plasma Discharges and Materials Processing by Lieberman has good descriptions of these types of things.
http://books.google.com/books?id=m0iOga ... navlinks_s

Relavant topics would include:
-Langmuir probes
-plasma sheaths
-Poisson's equation
-Child-langmuir law
-ambipolar diffustion
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