Yet another demo fusor (first runs)

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LucaTrussoni
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Yet another demo fusor (first runs)

Post by LucaTrussoni » Sat Aug 05, 2017 9:03 pm

This post describes my demo fusor and shows its first runs. I have been reading things in this forums for a while, but I decided to build something only when I found a bell jar at a reasonable price on ebay.
I started making the fusor around the bell: first, from an aluminium plate, four holes were drilled (three for pump, vacuum gauge and gas inlet, all ¼” SAE, and one for the electric feedthrough):
Piastra.jpg
Then a viton sheet was put between the aluminium plate and the bell jar, and an electric feedthrough was built form a spark candle:
VitonAndFeedThrough.jpg
Vacuum grease is applied on both sides of the viton sheet. A cylindric inner grid was built and connected with a bolt to the spark candle: the grid is made of harmonic steel wires kept together by 5 cents coin (euro cents has a 12 star circle, quite easy to find where to put six holes!).
This is the final setup (I had to build a wooden support for the fusor), you can see also the ground grid (that is a spring of harmonic steel):
FinalSetup.jpg
The electric power supplier is an unbranded unit, with knobs that can adjust voltage between 5 and 30 kV and current protection from 5 mA to 10 mA: I plan to build a HV voltmeter to check indications, but, if you trust the knobs, all the following pictures are obtainted at 5-7 kV with 7mA limit.
Vacuum is obtained with an air conditioning vacuum pump, and checked with a digital gauge (with a 200 micron Hg resolution). Unfortunately the minimum pressure I could achieve was 3.6 mm Hg: I think this can be due to poor pump or water contamination (lot of fog coming out of the pump…), since the chamber can maintain vacuum at its minimum pressure for about 6 hours.
These are a couple of pictures of the plasma obtained at 3.6-3.8 mmHg, the plasmoid has a nice clessidra shape:
clessidra_plasma.jpg
clessidra.jpg
Another picture:
oldrun_fusor.jpg
Here is a run without the ground grid (and a little higher pressure) showing discharges rising from the plate:
PlasmaNoGrid.jpg
During the first run I also built a guard around the bell (it has, in fact, imperfections) that was removed since it doesn’t heat and seems to survive vacuum safely.
Future plans are to try different gases (all there runs used air), to build an HV-voltmeter to check input voltage, and possibly to improve vacuum. Best everybody,
LT.

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Richard Hull
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Re: Yet another demo fusor (first runs)

Post by Richard Hull » Sun Aug 06, 2017 2:41 am

Interesting images and work. I have placed your name in the plasma club listing.

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.

ian_krase
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Re: Yet another demo fusor (first runs)

Post by ian_krase » Sun Aug 06, 2017 6:53 am

I highly recommend that you keep some form of shield on that bell jar. The larger the jar, the worse the risk for shattering, and that is even more the case with your power supply, which sounds to be rather more high performance than the average demo fusor supply. If you can feel a spot that's hotter than the rest on the outside of the bell jar, you need to cut the power and let it cool.

As far as getting the vacuum to be better:

Check the spark plug (some may have leaks, a leak that doesn't matter in a car is not good in vacuum, can possibly improve with Loctite 290), and all of the tubes. Also, may want to make sure the rim of the belljar is nice and flat and to maybe wiggle it around a bit as this can represent a kinda elusive slow leak.

LucaTrussoni
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Re: Yet another demo fusor (first runs)

Post by LucaTrussoni » Sun Aug 06, 2017 8:19 am

Richard: thank you very much!
Ian: I had a steel wire fence around the bell in the first run: I removed that for making photos, but I think I'll put that back on. Thanks for the advice on the loctite, I will definitly try it.
safeguard.jpg

ian_krase
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Re: Yet another demo fusor (first runs)

Post by ian_krase » Mon Aug 07, 2017 10:09 am

Loctite 290 is also good for sealing pipe threads if you don't want to solder them.

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Dennis P Brown
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Re: Yet another demo fusor (first runs)

Post by Dennis P Brown » Tue Aug 08, 2017 5:39 pm

Your power supply might do fusion if you make a proper chamber - people have achieved fusion at 19-20 kV and your supply might hit the required current at that voltage level. As such, you need to carefully design a chamber that best uses that supply (never use a glass chamber (except a small window) for real fusion work!) - a small chamber/cathode system with a higher pressure (30 microns) might be your best approach for that low power level (your power maybe is enough but very much on the low end which can make detection an issue.) Getting deuterium appears to be an issue that you might want to solve sooner rather than later. Neutron detection is straight forward but does require either money or a lot of electronics work. Your vacuum level is terrible and I agree with the suggestions assuming you have first checked the pump head pressure - that should be under twenty microns or else something isn't right with the pump! Don't chase phantom leaks if the pump isn't doing its job!

Building a high voltage meter is absolutely trivial compared to what you have already accomplished - a voltage divider works with any cheap voltmeter (place the resistors under oil makes it easier/more reliable); since your supply is highly dangerous, be very careful with it and be certain your ground is good and all wiring can handle the 30 kV. A HV meter shouldn't even be an issue. My guess is that the pump isn't going to do the job unless it is a two stage design and has enough capacity.

LucaTrussoni
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Re: Yet another demo fusor (first runs)

Post by LucaTrussoni » Wed Aug 09, 2017 7:01 pm

I think that the problem is in the pipes. Today I took one of them and I tried it with a different pump (double stage, 42 lt/min): a system made of the pump, the pipe and a gauge achieved 3.4 mm Hg only. So I suppose that I should include "get better pipes" in my future plans...

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Richard Hull
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Re: Yet another demo fusor (first runs)

Post by Richard Hull » Wed Aug 09, 2017 7:24 pm

A good pump at the inlet should hit .030mm of mercury (~30 microns). So, your pressure is 100 times too high!

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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