Chamber wall rainbows

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Greg Courville
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Chamber wall rainbows

Post by Greg Courville »

Last night I unbolted a couple of flanges on my chamber and a glint of color caught my eye. I shone a flashlight inside and saw this:
fusor_depo_colors.jpg
Quite a neat rainbow effect going on. I'm going to take a wild stab and speculate that we're looking at a range of oxide species formed by tungsten ions being shot into the stainless chamber wall and stealing oxygen from the chromium oxide layer.
A bit of quick research indicates that tungsten trioxide has a yellow color, and various non-stoichiometric species (near WO_3 but very slightly oxygen-deficient) produce colors such as blue, violet and chocolate brown...

Edit: Speaking of chocolate brown...
275cf_brown.jpg
Anyone else noticed an effect like this in their fusor?
John Futter
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Re: Chamber wall rainbows

Post by John Futter »

Greg
or more likely deposits of tungsten and general contaminants that are thin enough to interfere with differing wavelengths of light
hence the rainbow hues.
Clue does it rub off with a cotton rag rubbed very hard
if it stays more tungsten than contaminants
if it comes off little tungsten and much general rubbish off the walls
Greg Courville
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Re: Chamber wall rainbows

Post by Greg Courville »

John Futter wrote:Greg
or more likely deposits of tungsten and general contaminants that are thin enough to interfere with differing wavelengths of light
hence the rainbow hues.
Thin-film interference was my first thought as well. However, it struck me that the colors are out of order (yellow to violet to blue). XXXX EDIT: On second thought, I take that back. That is actually totally consistent with the color sequence you'd expect as the film thickness increases.

The subsequent discovery that yellow, violet and blue happen to be characteristic colors of tungsten oxides is what put me on my current hunch.
John Futter wrote:Clue does it rub off with a cotton rag rubbed very hard
It is quite resistant to cotton rag attack (no change, no deposits on rag).

When I have time I'll take another look and see if there's any angular dependence...
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Richard Hull
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Re: Chamber wall rainbows

Post by Richard Hull »

Very common and noted years ago. It is light interferance colorations based on monolayer depths, material compositiion, etc., all very pretty. The fabulous, lovely diamond patterning is also common and is a function of grid design and ion streamlining from same.

An old discussion related to glass viewport cleaning was had in the past. I have found that with a tungsten grid, only using a polishing compound and a lot of elbow grease will remove the brownish to bluish deposits from the glass.

For stainless steel grid deposition on glass, simple muriatic acid ( hydrochloric acid) will suffice to remove the deposits. Make sure to super wash, clean and maybe bake out in an oven, all ports after cleaning, before re-installation to cut the pump down time.

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
danielchristensen
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Re: Chamber wall rainbows

Post by danielchristensen »

Richard,
Is the reason why the diamonds form known?
Daniel
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Liam David
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Re: Chamber wall rainbows

Post by Liam David »

Since I have a small 2.75" 6-way chamber, running the grid white-hot for about an hour resulted in the disappearance in the rainbow pattern as the walls turned black. I have looked at the effects of this tungsten "bombardment" on aluminum foil under a SEM, and compared to regular foil, the damage is pretty clear. Just thought it might be interesting.

Regular Foil
Image

Tungsten deposited foil that was about 1cm from the plasma for about 10 minutes
Image

-Liam David
prestonbarrows
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Re: Chamber wall rainbows

Post by prestonbarrows »

The rainbow patterns are from dissimilar deposits creating thin film diffraction.

Once a thick enough layer is built up, the color shifts towards the natural appearance of whatever material is being deposited, usually greyish or brownish for steels/refractories or cuprics respectively.

Incident ions sputtering surfaces is a tried and true industrial method for deposition of materials. This is well known and covered in the literature and inDIY youtube videos.
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Richard Hull
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Re: Chamber wall rainbows

Post by Richard Hull »

The diamond patterns are typically related to the shapes of the outlets of a formal, spherical, geodesic grid structure. This structure was very common in early amateur fusors. This was the case years ago for me until we all realized that the geodesic shape grants nothing except beautiful multiple star rays and a grand needless complication associated with construction of the device's inner grid. There has been no data advanced to show that the far less complex three or four loop longitudial grid sphere is any less functional or produces more or less fusions than the stunningly lovely and carefully crafted, idealized, geodesic spherical wire grid.

I made all my grids to the geodesic from about 1997 until about 2004. They were all rather poorly made and not even close to the ideal symmetric sphere. However, they were all 100% fabulous in any and all images "through the looking glass". They were real things of beauty to behold. It reminds me of Morbius in the sci-fi movie, "The Forbidden Planet", telling all of the Earthlings to look away from the secret reaction that powered the planet as he opened a window to the core, and saying, "No one looks into the eye of the Gorgon and lives".

Image attached from fusor III. (circa 1999), Click on images to enlarge.... you just don't see cool fusion images like this these days here. AND.....You don't need to either. They signify nothing.

The learned here know it is the manner of operation and not a pretty grid that feeds th' bulldog in doing fusion.
Attachments
Fusor III looking like it is working in the ideal megawatt range!  In reality, it was barely getting 100,000 n/s!  Proof looks aren't everything or anything in fusion.
Fusor III looking like it is working in the ideal megawatt range! In reality, it was barely getting 100,000 n/s! Proof looks aren't everything or anything in fusion.
This is the "critter" you need to make for "them purdy pitures".  Probably my finest, but still short of the mark, geodesic (made of Hafnium wire)
This is the "critter" you need to make for "them purdy pitures". Probably my finest, but still short of the mark, geodesic (made of Hafnium wire)
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
Dan Tibbets
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Re: Chamber wall rainbows

Post by Dan Tibbets »

Tungsten oxide coating the chamber and electrodes has been a problem for Lawrence Plasma Physics- the dense plasma focus machine. since going to tungsten electrodes, they have been wrestling with this problem for about a year.

http://lppfusion.com/experiments-confer ... mpurities/

Dan Tibbets
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Richard Hull
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Re: Chamber wall rainbows

Post by Richard Hull »

Tungsten can have a continuous "water cycling" issue. This is a "conveyor belt" issue of outgassing and re-absorption. It is identified in many 40's and 50's texts on vacuum tube manufacture.
it is especially problematic in monolayer and thin film W depositions. Not a real issue with fusors and their higher pressure working regime. I think it was dubbed the "tungsten water cycle" in old texts.

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
Dan Knapp
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Re: Chamber wall rainbows

Post by Dan Knapp »

In an effort to understand why I am seeing contamination of the anode (left in attached photo) but not the cathodes (right) in a Penning trap, I turned up a very old paper that explains these deposits as carbon formed by electron bombardment of organic surface contaminants (e.g. pump oil vapor). This is a likely source of the "chamber wall rainbows" in fusors.
Insulating contaminant layers create problems in ion optical systems when the surfaces charge up. An old preventive was to coat electrode surfaces with colloidal graphite (Aquadag). If these electron induced contaminant layers are elemental carbon and therefore conductive, it may be that they aren't problematic in regard to surface charging and might even be helpful.
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electron induced contamination2.pdf
electron induced contamination paper
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photo of Penning trap anode contamination.
photo of Penning trap anode contamination.
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