FAQ - A Demo Fusor Plasma Pictorial

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Jon Rosenstiel
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FAQ - A Demo Fusor Plasma Pictorial

Post by Jon Rosenstiel » Mon Jan 14, 2008 5:48 pm

Setup:
Bell jar demo fusor running on air. Outer grid is constructed of 0.025” stainless steel safety wire and has a diameter of 6". Inner grid is constructed of 0.020” tantalum wire and has a diameter of 1.24”.

Power supply consists of a full-wave rectified 12 kV, 30 mA neon sign transformer controlled by a variable transformer. (Variac)

Vacuum system consists of a small Leybold D1.6B two-stage direct drive pump. (1.6 cu-meters / hour) Lowest attainable pressure in the bell jar is ~15 mTorr. An MKS 10 Torr capacitance manometer was used to measure the chamber pressure. The bell jar had been vented to and was at atmospheric pressure just prior to pump-down and image capture.

Images were taken with a tripod mounted Canon EOS 400D. All images were captured using the same camera settings. (1/8 second, f5.6, ISO 400) Images were cropped, sharpened, and reduced in size using Paint Shop Pro.

For the sake of load times I’m dividing up the ten images I have to share into two separate posts. This post will comprise of 1 Torr through 100 mTorr, and the next post will comprise of 50 mTorr through 15 mTorr. I took two photos at 15 mTorr; the first was taken when the chamber pressure first reached 15 mTorr. (20 ~ 25 minutes into the pump-down process). The second image was taken after a good five hours of pumping.

Jon Rosenstiel
Attachments
1 TorrA.jpg
1 TorrA.jpg (48.94 KiB) Viewed 2657 times
600 mTorrA.jpg
600 mTorrA.jpg (41.17 KiB) Viewed 2657 times
400 mTorrA.jpg
400 mTorrA.jpg (39.54 KiB) Viewed 2657 times
200 mTorrA.jpg
200 mTorrA.jpg (45.37 KiB) Viewed 2657 times
100 mTorrA.jpg
100 mTorrA.jpg (49.88 KiB) Viewed 2657 times
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Jon Rosenstiel
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Re: A Demo Fusor Plasma Pictorial

Post by Jon Rosenstiel » Mon Jan 14, 2008 5:50 pm

The remaining images...
Attachments
50 mTorrA.jpg
50 mTorrA.jpg (50.48 KiB) Viewed 2655 times
25 mTorrA.jpg
25 mTorrA.jpg (58.18 KiB) Viewed 2655 times
20 mTorrA.jpg
20 mTorrA.jpg (49.75 KiB) Viewed 2655 times
15 mTorrA.jpg
15 mTorrA.jpg (62.23 KiB) Viewed 2655 times
I like old-timey heavy electronics that you don't have to hold down
with one hand while pushing the on/off button with the other.

DaveC
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Re: A Demo Fusor Plasma Pictorial

Post by DaveC » Mon Jan 14, 2008 8:52 pm

Very nice series, Jon!

This should make a good set of reference shots for everyone.

I particularly like that you were able to maintain 5 mA current level so that the rise in potential with the fall in pressure can clearly be seen.

You apparently had no problems from the plasma "rays" doing localized heating at the bell jar walls, at lower pressures.

Nicely done, indeed.

Dave Cooper

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Re: A Demo Fusor Plasma Pictorial

Post by Wilfried Heil » Mon Jan 14, 2008 9:49 pm

Nice tutorial and photographs.
Hope this gets reference status here and can be found again later. As a FAQ maybe?

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Re: A Demo Fusor Plasma Pictorial

Post by Starfire » Tue Jan 15, 2008 11:43 am

I second previous comments - nice work Jon - well worth while.
Tks.

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Richard Hull
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Re: A Demo Fusor Plasma Pictorial

Post by Richard Hull » Tue Jan 15, 2008 2:54 pm

I have FAQ'd this one on my own. This is a real winner for newbies to the vacuum world. and a great set of "gauge blocks" for folks wondering whether their surplus TC gauge is telling the right story or not.

Often the old hands have seen an image like the 100mtorr image and the user has said his gauge was reading 15 microns. We knew better. With this set of images, the amateur who hasn't got a clue can set his TC gauge pot to a relatively close value. (though a simple current match to the gauge tube spec is what is really needed) Some amateurs have no way of hitting the required submicron level needed to zero a TC gauge.

A long overdue exercise and very well presented Jon.

Ricahrd Hull
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Jon Rosenstiel
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Re: A Demo Fusor Plasma Pictorial

Post by Jon Rosenstiel » Tue Jan 15, 2008 4:11 pm

Dave-

I did a couple of things to minimize localized heating of the bell jar walls. One, I kept run times as short as possible (~10 seconds). And two, I used an NIB magnet to "steer" the main electron beam away from the bell jar wall.

Jon Rosenstiel
I like old-timey heavy electronics that you don't have to hold down
with one hand while pushing the on/off button with the other.

Jon Rosenstiel
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Joined: Thu Jun 28, 2001 5:30 am
Real name: Jon Rosenstiel
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Re: A Demo Fusor Plasma Pictorial

Post by Jon Rosenstiel » Tue Jan 15, 2008 4:19 pm

Richard-
Adding "FAQ" to the subject line was a good idea... something I hadn't even considered.

Jon Rosenstiel
I like old-timey heavy electronics that you don't have to hold down
with one hand while pushing the on/off button with the other.

mobious
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Re: A Demo Fusor Plasma Pictorial

Post by mobious » Wed Jan 16, 2008 3:24 am

Very helpful Jon....as a newbie this gives a little illustration to put with the instructions.

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Carl Willis
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Re: FAQ - A Demo Fusor Plasma Pictorial

Post by Carl Willis » Wed Jan 16, 2008 5:21 pm

Welcome to the Plasma Club, Jon. (Hah!)

This is a beautiful and definitive photo set. "FAQ" would be an appropriate designation even if no writing whatsoever accompanied them.

-Carl
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