My New Fusor design; update

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Dennis P Brown
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My New Fusor design; update

Post by Dennis P Brown »

Without a doubt my high voltage (HV) feed is leaking on my new fusor and it is significant; though tests indicate - via dust off - that it is 'minor' relative to 10^-5 torr (Turbo running, of course.)

Apparently not. Dust Off and alcohol have limitations in detecting significant but not major leaks. They can locate an issue but certainly not determine its magnitude - a very powerful two stage pump and turbo can make any non-major leak look small (apparently) during operation and leak detection (in the 10^-5 torr readings range applying dust off only varied the gauge by three or four values, not decades as I would expect for a significant leak.) Till I replaced the questionable components (located with dust off) with a 'blank-off", the full extent of the problem was not readily apparent. Then it was obvious.

With just that HV component removed my complete system reach's 1.5 micron in a few minutes (the system has a lot of connections and a rather large chamber) and leak back rate is one micron a minute (unbaked, right after exposure to air. But for a clean, seasoned system generally held under some vacuum I've found that this is normal if there are only virtual leaks present caused by the short exposure.)

To better confirm this value I cross checked the installed TC reading against a cold cathode gauge when the fusor system was at bottom pressure (for the TC.) The two units agree within half a micron (1.5 micron vs. 1.9 micron.) The pump has been previously checked against a calibrated gauge some years ago (under1.5 micron pressure on the head using a minimum of connections) but it is nice to get a cross reference between dis-similar vacuum gauge units simultaneously and recheck the pump after a few years in storage.

Then in a test with the 'bad' HV feed/plate assembly installed, the bottom pressure was only 20 microns at best (mechanical pump on the system) and leak back rate of 250 microns/min.

So, I will return to my original design for a HV feed-thru - a large glass plate with a stainless steel rod anchored with epoxy (This time, ceramic epoxy); this design was rather successful with my first fusor. I'll need to diamond cut the hole (far too easy with these inexpensive diamond hole saw units from China - I have a whole set (to 1 inch dia.) for under $20. Ridiculous price and they hold up very well.) I'll use part of the old HV system so that isn't wasted.

I am slowly collecting and getting my host of neutron detector systems together and hopefully, ready sooner rather than later. But certainly first order of business is that I need a working fusor - lol. Getting activation, as Richard so correctly pointed out, is the ultimate first proof and best manner after a bubble detector. Aside: been testing my Geiger counter system - one tube failed but I have a spare that works.

In time, I will test each neutron detector type: a new 3He tube with an amp & power supply that interfaces & controlled by a computer & special software program; a BF3 tube proven years ago, and another 3He tube (untested) - both these units can be hooked up to my Spectech system (which now interfaces to a computer as well.) Finally, a neutron sensitive scintillation detector I built from scratch - needs lead shielding, badly. Needless to say, I'd really like to check all these systems and if I don't go off a tangent (not holding my breath - there are a lot of neat experiments I really want to do), move to calibrate these detectors via a bubble detector.
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Richard Hull
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Re: My New Fusor design; update

Post by Richard Hull »

Ever since 2004 on fusor IV and now fusor V, My HV feed through has had a leak, slow, on the order of 1 micron/min in a sealed dead fusor right after shut down, and yet, it serves to do great fusion.
Good luck with your new design and ideas for experiment.

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
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russssellcrow
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Re: My New Fusor design; update

Post by russssellcrow »

Good report!

Dennis, can you post a pic of your glass plate feedthrough? As you know, porcelain feedthroughs are outrageously priced from suppliers, and any help in breaking the cost barrier is appreciated.

Today I'm experimenting with a melt-in CPVC insulator for the bottom of a spark plug. CPVC has 4X the standoff voltage of porcelain, ~50kV/mm. The downside is heat resistance and thus outgassing. So the plan is to drive the CPVC insulator to full contact with the spark plug bottomside, inside a Borosilicate jacket for heat shielding. Then I'll close the Pyrex jacket with a torch around the electrode (Tungsten Oxide wets Borosilicate well and the thermal expansion coefficients are very close). It's a balancing act for sure, but I think an experiment worth spending the day upon.
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Joe Gayo
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Re: My New Fusor design; update

Post by Joe Gayo »

Not everyone has $162.18, but it seems like the most economical way to achieve a high voltage feedthrough with good performance (if the airside is submerged in oil, 50kV+ is possible) is the classic fluted design - https://mpfpi.com/shop/power-feedthroug ... a0230-1-w/ . This could be welded or a radial o-ring seal could be used with a custom flange (use a step in the flange to stop the feedthrough from being sucked into the vacuum).
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Mark Rowley
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Re: My New Fusor design; update

Post by Mark Rowley »

Joes suggestion is almost exactly what Richard did years ago and which I followed suit with soon after. By adding Carl Willis's oil socket design more than 80kV was achievable. Highly recommended fool-proof arrangement.

Mark Rowley
Matt_Gibson
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Re: My New Fusor design; update

Post by Matt_Gibson »

Any ideas how one could go about using an oil socket design for a feed through oriented on top, instead of below, the chamber? It would be a major pain for me to relocate the feed through on the bottom…
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Richard Hull
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Re: My New Fusor design; update

Post by Richard Hull »

Oil sealing in connection with a feedthrough in a vacuum system is always a real pain. One silly oil or even its vapor leak and you have a mess. Good luck.

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
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Dennis P Brown
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Re: My New Fusor design; update

Post by Dennis P Brown »

I hope to disassemble the fusor soon and I will post detailed images of the feed-thru. For now, I'll include some of the external shots. The glass plate I got from a person that sells Pyrex glass telescope blanks. I used a very inexpensive diamond circular drill blade that easily cut thru the pyrex. Use epoxy to seal. The main rod is threaded brass (had on hand.) The lower section (not visible) is a ceramic hollow tube that the metal rod passes thru. The actual cathode cage is just a steel welding rod bent into a cage-like form.

Right now, it handles the full 33 kV at 30 ma and without any leakage or corona issues. Also, stays rather cool while the cathode glows white hot. I need to test my 3He detector before I break seal on the fusor - the system is out gassing very little (20 microns/hr) and I want to make a real run before opening to the air.

Relative to sealing a cathode I'm not sure an oil seal is ideal (spillage can be a mess to clean up - been there) but I keep my ballast resisters under oil to cool them and prevent any corona issues. Use to keep the diodes but that was just a bridge too far, mess wise.

That all said, I house the metal section of the cathode (the part in the air) inside of 1/2 inch plastic plumbing tubing to further insulate it. This simple system appears to work well.
Attachments
Cathode Assembly
Cathode Assembly
Cathode w/o plastic piping & HV cable
Cathode w/o plastic piping & HV cable
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Richard Hull
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Re: My New Fusor design; update

Post by Richard Hull »

A very interesting feed through to say the least. The huge relief, (giant opening under glass), is great for electrical stress reduction.

Do you rely on the vacuum to compress the glass onto the gasket via the vacuum? I would imagine you have some sort of machined, bolted ring on top to bolt the glass lightly to the gasket?

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
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Dennis P Brown
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Re: My New Fusor design; update

Post by Dennis P Brown »

I use to lock it down via the tapped holes but realized it was a waste of effort (and a good way to crack the glass when I used thinner pieces). So yes I use pressure differential and it works very well - the rate of leakage is very low for the system/HV feed but between that and out gassing I see 20 microns an hour. For the short runs I've done (10 minutes) the cathode turned white hot but the upper HV post remained cool.
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Dennis P Brown
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Re: My New Fusor design; update

Post by Dennis P Brown »

Here are the promised images of the inner side of the HV feed-thru; the leakage is extremely small - even after opening to the air (for pic's) and closing, the system rose from 17 microns to 2.6 torr in a day. Obviously, mostly out gassing.
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Cathode assembly
Cathode assembly
Cathode at 17 kV
Cathode at 17 kV
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Richard Hull
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Re: My New Fusor design; update

Post by Richard Hull »

I'm glad you are busy at doing stuff. My lab is like a refrigerator. Not fusion friendly this time of year. ( sorry, not people friendly) Fusion is not afraid of the VA weather as at 40kv the hottest possible deuteron would be at 440 million kelvins. Of course most would be much cooler in the 100 million kelvin range. Still, I gotta' stand their and run the thing. I don't enjoy bundling up like Nanook of the north, resembling the Bibendum.

A case for remote and televised operation from a warm easy chair with pizza and a soda. Just need a bunch of geared motors, feedback stuff and a trunk cable. Good luck with me doing that...Then I'll just wanna' sit in the air conditioned easy chair in the summer to run th' thing. Let's keep it difficult and tedious. I have always been up close and personal with my fusor. A touchy, feely kinda' guy.

I assume you smaller lab is heated. Sometimes bigger is not better. Good luck in getting all that air and moisture out after the "open up and look-see"

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
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Dennis P Brown
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Re: My New Fusor design; update

Post by Dennis P Brown »

Yes, mine is heated (and has AC for the summer.) I'll spend some of this weekend trying to calibrate a series of vacuum detectors (both micron and high vac) and a number of vacuum detectors. Something I've been needing to do for some time for this and other future projects. If I get the time, I might look at the 3He detector.

But at some point (sooner rather then later) I really need to build a very low current variable 2 kV power supply that uses a battery for primary power (made one in in the past but that has long since been parted out/cannibalized - it was too space intensive and supplied far too much current.) Then I need to build a voltage divider to adapt a counter system for use with a higher voltage detector (my old BF3 tube). It seems there are always side projects to complete before a main project can be addressed - working on fusors seems to create side projects like the mythical hydra grows new heads ;)
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