Archived - New light

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
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Adam Szendrey
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Archived - New light

Post by Adam Szendrey » Sat Jan 10, 2015 7:08 pm

Just to get some plasma into my vacuum chamber after such a long time I hooked a small flyback to it. My HV diode doesn't seem to be able to keep up with the frequency or it's busted otherwise, so what you see here is AC air plasma, making everything quite a bit more diffuse. Still it was nice seeing "life in the flask" again! And no matter how many times I see it I find plasma phenomenon absolutely beautiful. I'll dig up a couple of HV diodes eventually and test using a proper supply.
I made a video of the pumpdown and venting in HD. It's realy nice to see how the plasma changes with pressure, in both "directions" (decreasing, or increasing pressure). A pressure display in the corner of the video would be great but I don't have my (good) gauge yet. Would be rather educational to those here who build demo fusors and very often get the pressure wrong, not knowing how the plasma "should" look.
I can't seem to pump the chamber to plasma extinction but this might be due to using AC (causes more ionisation, plasma stays alive to a lower pressure...?). Although I'm pretty sure I have some leaks too. Nothing horrible tho! The fact that the two jets are still visible tells me I'm not pumping as far down as I used to years ago.

https://www.youtube.com/watch?v=gZzKyN0iee0
acpoissor2015.jpg
AC plasma

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Adam Szendrey
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Re: New light

Post by Adam Szendrey » Sat Jan 10, 2015 7:58 pm

A very quick and dirty toroid grid! The center grid is grounded. Interestingly the toroidal plasma is much more defined if I use a grid as the center "anode" instead of a solid cylinder. I tried both.
actorus.jpg

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Chris Bradley
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Re: New light

Post by Chris Bradley » Sat Jan 10, 2015 10:34 pm

Your [top] fusor will act as a rectifier when you can see the 'beaming' as this is a self-stimulating beam sputtering electrons that ionise locally and therefore sustain the beam.

You could try monitoring the currents, and it would be interesting to see if you can quantity the degree of rectification.

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Adam Szendrey
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Re: New light

Post by Adam Szendrey » Sat Jan 10, 2015 11:35 pm

Aye! I could try to do that with my scope, with a proper HV probe, and a current meas. resistor in series with the fusor. My other instruments won't measure in the freq. range of the flyback, and they are not TRMS (I need to get some proper instrumentation...).

All the while I found a replacement diode, and the result is the trademark star! (not this bright to the naked eye of course, I did increase the contrast slightly)
starmode_2015_small.jpg
Although the torus in this setup was above the center grid, it did produce a really pretty pattern at low vacuum levels (it formed a plasma helix basically).
torus_lowvac.jpg
I did take a photo at micron levels as well but it's very diffuse because of the fact that the toroid grid is above the spherical one. I'll do a different experiment to improve the toroidal mode.

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Richard Hull
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Re: New light

Post by Richard Hull » Sun Jan 11, 2015 7:47 am

Nice images. Thanks for sharing.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Adam Szendrey
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Re: Archived - New light

Post by Adam Szendrey » Mon Jan 12, 2015 8:57 pm

Having two HV feedthroughs is really nice. Although these voltages are quite low (relatively speaking).

Next steps:
Buy KJL vacuum gauge
Build a couple of decent grids from something more suitable than copper or aluminium wire (tungsten or titanium, or stainless wire maybe).
Get some proper metrology together (electrical, and radiological). I was thinking about how to quantify grid geometries without using deuterium to indicate efficiency by neutron count. I haven't really thought it through but I was considering maybe measuring x-rays. Actually the lack of 'em...maybe less xrays would mean better electron trapping? Less off the buggers wasting energy in the form of x rays... I'm also considering combining a cylindrical grid and an axial magnetic field (ala "magnetron").
Decent HV supply. For which I'll first need a better place for the system than my kitchen. And this is the most difficult part. This might not happen for a year or so, until I can get that cellar built.

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Adam Szendrey
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Re: Archived - New light

Post by Adam Szendrey » Thu Feb 26, 2015 12:30 pm

A little note here:
It's interesting to observe the degradation of the spherical grid. I did it quick and dirty quite a few years ago, and it was used several times, on occasion for a long period of time. And even though the power supplies I used never had a power rating high enough to make the grid glow red, it clearly is affected by operation. Originally the loops, which are made of welding wire, had a copper coating, it came as no surprise that this coating is long gone, it was basically plasma etched, sputtered away (it ended up, on the ceramic of the feedthrough and on my viewport glass, and on the inner chamber walls). The loops, originally had some tension, they wanted to "open", now they are very stiff (caused by temperature cycling). And, the soldering at the "northen" pole of the sphere is gradually becoming brittle. I wonder how much the grid heats up in there, even though it doesn't glow from the heat, I'm sure there is considerable temperature cycling, annealing, going on (although the highest temperatures are below the melting point of the solder, so most probably below 200-250 deg. C). Just thought I'd share, although I'm sure pretty much everyone here with a fusor has observed the same effects.

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Richard Hull
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Re: Archived - New light

Post by Richard Hull » Thu Feb 26, 2015 10:06 pm

Such grid effects are as common as the sea sickness. water breakdown to hydrogen and oxygen causes embrittlement. No amount of heat cycling in a true fusor will ever anneal the wire. Quite the opposite. The deuterium, (hydrogen), will embrittle the grid as the hydrogen is constantly driven into its interstitial structure. Hydrogen embrittlement is a long known and well studied phenomenon in the metals and material science biz. Tungsten, titanium, nickel, the platinum group and many refractory metals are especially susceptible.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Adam Szendrey
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Re: Archived - New light

Post by Adam Szendrey » Thu Feb 26, 2015 11:17 pm

Thanks Richard! That makes perfect sense. Now I kind of recall reading about that, my memory failed me!

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