Conversion to a Small Chamber Fusor

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Dennis P Brown
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Conversion to a Small Chamber Fusor

Post by Dennis P Brown » Thu Dec 28, 2017 4:14 pm

Due to the results from my experiment showing that a "smaller" chamber can significantly increase a fusor's neutron flux for identical power levels, I dis-assembled my existing fusor and removed its main chamber. Lucky, (or maybe, just good design on my part ...no, luck) I already have a rather small chamber that formed part of my original fusor/vacuum system.

This small chamber was used as an adapter to connected the large chamber body to the DP. Also, this small chamber had attachment ports for my micron (TC) and ion gauge tubes, and provided the support and mechanics of my butterfly gate valve. Better still, since the upper adapter plate that is part of the small chamber system - and was used to adapt to the large chamber - has an o-ring seal that allows my current high voltage feed-thru system and view port to still work. All I had to do was shorten the inner ceramic standoff to allow the cathode to be centered in the new small chamber.

I just tested the new system (no HV) and it is holding high vac (mid-10^-5 torr as before. With time this should improve to 10^-6 torr as before; likely some water got into the system when I broke down the water cooling lines.)

I need to still install my deuterium line/entry port to the small chamber. Also, ground lines have to be reconnected and a few minor issues addressed before I can test the system and see what neutron flux I get (assuming other issues don't occur preventing this - if it is one thing I've learned with building/operating a fusor system: What can go wrong, generally does go wrong whenever anything has been changed.

Well, step one (dis-assembly), step two (re-assembly), and step three (Vacuum test) have, at least, all gone smoothly and successfully (of course, my DP heater wires broke off requiring that to be repaired - well, needed to be updated, anyway.)

Below are some related pictures.
Attachments
MVC-038L.JPG
Entire Fusor System (Power supply to Left; D2 supply to the right)
MVC-035L.JPG
Small Chamber Fusor (note electrode on top)
MVC-036L.JPG
Small Chamber in Support System
MVC-037L.JPG
Close up of the new fusor chamber (small)
MVC-039L.JPG
Original Large Chamber with attachments and water cooling lines (a future boat anchor?)

User avatar
Dennis P Brown
Posts: 1712
Joined: Sun May 20, 2012 2:46 pm
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: Conversion to a Small Chamber Fusor

Post by Dennis P Brown » Fri Dec 29, 2017 5:26 pm

Added the D2 line and tested the system under high voltage. Very difficult to control - seasoning helped but didn't cure that issue at all.

Found (finally after a lot of effort) a semi-stable operating region for my system - 20/21 kV @ 43 microns. Power (after chasing both the current and pressure) finally stabilized at 20 ma. Managed only a bout two minutes and detected no neutrons on the bubble detector (not too surprised considering the length of time.) However, didn't like the color of the discharge so need to look into leaks now (maybe the heat caused issues on my electrode feed-thru.)

At least for may unit, operating at these high pressures is not stable; while size and geometry of the chamber/electrode will play into this I will say that at these high pressures due to small volume, even with the greater increase in ions, there are, apparently, innate issues with controlling the pressure - that is, such a small volume really will change pressure a good bit when the plasma starts up and heats the gas. Also, little buffering when voltage varies leading to current changes which causes pressure changes; these can grow exponentially and that isn't fun to deal with on a control side.

Either my system design needs improvement (not unlikely) or people did not bother to report these issues when determining neutron production for their working small fusors.

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Richard Hull
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Re: Conversion to a Small Chamber Fusor

Post by Richard Hull » Fri Dec 29, 2017 10:07 pm

You should remember that others with small systems grew into them and you may have to do the same. Controlling the system might be more difficult or just completely different from the manner we folks have become used to controlling larger fusors. There is a trick to it all, for sure.

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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