First plasma

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Finn Hammer
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First plasma

Post by Finn Hammer » Sat Jun 10, 2017 9:39 pm

It takes time to build a real fusor, and anyway, I thought I had better get my hands on creating low pressures so I set out to build just a demo type fusor.
The vessel is a pot from Ikea, it measures 260mm diametre by 200mm deep, and has a glass lid, which I found to be handy, since it could then double as high voltage feedthrough and viewport simultaneously.
tn_DSC_9574.JPG
Grid and highvoltage feedthrough in the centre of the viewport
I jerry rigged it up with plumbing fittings, and this did not get pretty. The hose from the pump to the kettle is also less than good, but this is what I had laying around.
You can see the setup here:
tn_DSC_9565.JPG
Pot from Ikea, cheap pump, digital thermocouple and homemade 20000:1 voltage probe
During the construction of the demo, I thought I would replace the Ikea lid with a nice 12mm thick glass disk I had from a record player, this turned out to be a disaster, because it imploded with a loud crack, and one fragment cut me deep in the chin, so I had to go to hospital to get it glued together. No, they don't use stitches anymore, but at least it did not hit me in the eye.
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Schrapnell from improper use of hardened glass
Back from the hospital, I started to pump down and hunt for leaks. I am not a fan of teflon tape, so in the end, all the fittings got soldered together with tin, and the hoses got tied with wire. In the end, the pressure setteled at 100micron, that is as deep as it would go.

The powersupply is a halfbridge switcher from Science First, I had it laying around from some plasma globe work I did some years ago, and it turned out to work fine. The plasma lights up at around 2,5kV and on the pictures the voltage is 8kV. The current measured across a 1K resistor is 8-10mA
tn_DSC_9558.JPG
First Plasma
Here from another angle:
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Interesting to see, how shiny and clean the copper grid was after just about 10 minutes of being submerged in the plasma.
It does not seem to make a huge difference whether the grid is driven by AC, or if it is negative with respect to the kettle. But if it gets positive, things get really funky, the whole volume lights up quite uniformly, and the grid does not create any effects that makes it stand out, like when it is negative.
DSC_9562.jpg
Kettle when the grid is positive
Anyway, a good and learningfull day, I can't wait til the nice litle inverter tig welder arrives, so I can get some tight joints.

Cheers, Finn Hammer

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Richard Hull
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Re: First plasma

Post by Richard Hull » Sun Jun 11, 2017 4:46 pm

We have constantly warned in the FAQs against the use of glass enclosure evacuation chambers. Even xppensive bell jars of Pyrex made for vacuum work are dangerous as simple demo fusors due to ion beam impact.

Learning the hard way always works great, if you live to apply the lesson learned. Suppose the glass shard had hit your jugular?

At least you got back on the horse. Lesser folks would have abandoned the effort all together.

Thanks for sharing the images of the disaster and full disclosure. this post will act as a hard reminder to many, I am sure.

Good plasma, You are now placed in the plasma club listing.

Richard Hull

P.S.

My first demo fusor was in a plastic dessicator designed to function under vacuum made of unbreakable polycarbonate. The ultimate pressure was limited by outgassing and ion impact vaporizing the plastic at higher currents. The best I ever did was about 35 microns.

This and several other archived postings of my fusor image history are all on page #15 in Images du Jour. I gathered and posted them in order back in 2008 and all are on page 15.

I have saved you a bit of trouble here are the links my first fusor mentioned above is in link 2 below.....Be sure to click on the images to enlarge. Check out the whole series of progressive historical images:

viewtopic.php?f=18&t=7793
viewtopic.php?f=18&t=7794
viewtopic.php?f=18&t=7795
viewtopic.php?f=18&t=7796
viewtopic.php?f=18&t=7797

There is a lot of great images in the older pages in image du jour.
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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Finn Hammer
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Re: First plasma

Post by Finn Hammer » Sun Jun 11, 2017 8:09 pm

Jugular? well that would have been bad....

Anyway, thanks for putting me on the plasma list. Having spent the better part of the last 15 years trying to _avoid_ corona in my constructions, I frankly did not expect problems creating a plasma, but I forgot the challenges of the vacuum, which is new to me.
For a while I have been pondering that perhaps I would have been better off spending some time with a simple bell jar, to get a feel for things, but it is my nature to plunge directly into things.
I know now that there are no shortcuts when it comes to creating a solid sustainable vacuum, proper construction techniques are needed, and what has up to now seemed to me like terrifically overbuilt, is now understood as being a necessity.
I also want to thank you for the links, where one in particular sparked my interest, and that is the one which leads to the pictures of Joe Zambelli's efforts, since he was on the path where I am just about to embark, the hands on construction of the fusor vessel. The jigs and fixtures he created to aid during tig welding are very usefull to me.

Cheers, Finn Hammer

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Re: First plasma

Post by ian_krase » Mon Jun 12, 2017 3:31 am

Yeah, I imagine you now see why safety shields and/or protection film are so important, especially when applying vacuum for the first time. Most successful large glass elements are either hollow (tubes, cylinders, bell jars) or much thicker than yours for the diameter. Plus a drilled hole (not sure if you drilled one before shattering) or nicks/chips/cracks massively weaken glass.

The thing about ion beams heating up glass in spots and breaking it is no joke either. My vacuum chamber (with a 4 inch, 1/4 inch thick glass cylinder) was originally used as a sputter chamber, which does coat glass with metal but doesn't heat it up very much. Later, with a demo fusor grid installed, I was surprised by how quickly a warm spot developed. It surely gets worse with more power. And that was the end of testing that.

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Richard Hull
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Re: First plasma

Post by Richard Hull » Mon Jun 12, 2017 7:50 pm

I have told this before. I actually pushed fusor III towards fusion. As seen in my references above, fusor III was a formal kimax bell jar. I ceased the effort when I had about 150 watts going into it with the fabulous needle pointed star mode of 9 rays and saw the glass at two points heat to a brilliant yellow in tiny spots....Suddenly, a 1/4-inch flake of glass popped off the inner wall at one ray point!

I never ran fusor III again, except as an under powered, show and tell device as I machined fusor IV's chamber into being over the next two months.

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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