Fusor V construction - the process long running

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Jim Kovalchick
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Re: Fusor V construction - the process long running

Post by Jim Kovalchick » Wed Apr 01, 2020 1:03 pm

With my cross, the xrays are where you might imagine, the view port and feedthrough. At higher voltages, the cross tubes become transparent. The conflat fittings have some bulk them so that helps except out the beam target ends. I have now wrapped the cross tubes with a double layer of lead for a total of about 1/8" inch. I have a piece of thick lead on each beam end and a piece over my view port. Not much I can do about my feedthrough, but I have it facing to the back. I would like to do something different with my camera situation, but that's what I have for now. I dont have to spend time near my fusor except to take a neutron reading with a PNC and placing a neutron oven target. I am less than 1 mrem/he generally about 1 foot out at 40 kV now that I shielded.
I am working on permanent mounting of neutron detection to eliminate that dose as well.

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Richard Hull
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Re: Fusor V construction - the process long running

Post by Richard Hull » Wed Apr 01, 2020 7:43 pm

I was thinking more in the line of a single total shield. I think, at first, I'll just do a "shadow cone" shield for myself if it gets intense. Thanks for the input. Lead wrap of the tube portion is a good idea.

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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Richard Hull
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Re: Fusor V construction - the process long running

Post by Richard Hull » Sat Apr 04, 2020 6:50 am

Well, take a good look at what is the finished fusor V. It may be the last time you see it!

I ran the system most of the evening and did fusion, but only a tiny amount. Extremely disappointing. Running at 29kv, 10ma and 23 microns. I got only 100 counts on the He3 counters in a minute on my best run.
I am ready to tear it down and put fusor IV back up in modified form. Boy, am I ready! However, I might try one of two more things in the effort before going back to fusor IV. It will keep me busy, at least.

I find that the heating is an issue and in spite of the additional fuel pressure, I did not see much to my satisfaction.

I am convinced it is all about the uniform huge surface area of the sphere that is the winner and 6-inch hemispheres are ideal up to about 60-70 kv.

For those with these systems, have any of you measured a favored direction for neutron emission, like the target conflats? I will probably try to cobble up and test a BC-720 system that is reliable and compact.

Richard Hull
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Fusor V 4.4 (2).JPG
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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Jim Kovalchick
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Re: Fusor V construction - the process long running

Post by Jim Kovalchick » Sat Apr 04, 2020 11:49 am

I sit my pnc on top of one of my beam end blanks. At 40 kV and 10 mA I get about 750 cpm. The same BF3 tube measured 400 cpm held against your fusor IV doing a million n/sec. I'm sure my total neutrons are less, but the effective neutron flux I can get close to seems higher.

I think Jon R said that small grid size differences changed his numbers a lot. I would try different grids before giving up.

I'm also concerned about grid and chamber heating. I perceive my neutron numbers flattening as I raise voltage and current as things heat up. I really need to connect my tube to a scaler to really understand it.

I am also toying with the idea of putting metal inserts on my cross ends to bring it all closer in. If you look at Jon's cube, his blanks are closer to the grid than a 6 way cross brings it.

Just some thoughts,
Jim K

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Richard Hull
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Re: Fusor V construction - the process long running

Post by Richard Hull » Sat Apr 04, 2020 10:51 pm

As I see it, the grid in the cross systems are electron emitters, located where we do not want them. We want electron emitters at the blanks/targets where they can ionized the deuterium. To this end I hope to try a couple of things to save fusor V. Tungsten needles embeded in a circle way from the center of the flange might help. I attach a diagram here.

Also, some electrostatic ion guns might help if attached to both facing flanges. Another diagram here Note: the more current you can pour into the gun, the better. 10-20 ma is fine. The supply being positive is a snap to build.

Richard Hull
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Electrostatic Ion gun.jpg
W needle ionizer.jpg
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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Scott Moroch
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Re: Fusor V construction - the process long running

Post by Scott Moroch » Sun Apr 05, 2020 12:46 am

I am curious why the tungsten needle in your ion source is at a negative bias with respect to the shell?

I would also suggest a single hole or group of holes around the center axis, rather than many perforations.

I have attached a picture of a successful deuterium ion source I have built. 1.2 kV across the glass, followed by a 20kV accelerating gap (in this case you would just use the grid).
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Deuteron Ion Source.jpg
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Richard Hull
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Re: Fusor V construction - the process long running

Post by Richard Hull » Sun Apr 05, 2020 4:53 am

In the gun, I did get the polarity backwards. Sorry 'bout that. I have corrected it, now, in the above original post. the bias on the needle makes it an electron high field emissive source to ionize the gas and the grounded (now negative) perforated plate attracts the deuterons some, as canal rays will go through the plate and see the huge attractive negative grid electrode. The patterned hole plate is a very inefficient positive HV extractor.

I did not mean to shotgun blast holes. Look at the nicely patterned electrostatic guns in the photos of Farnsworth's team......holes like that...

I repost the image here from my Farnsowrth history group. note the rather large radial circular holes and a rather tiny central hole




Richard Hull
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Electrostatic guns.jpg
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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Maciek Szymanski
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Re: Fusor V construction - the process long running

Post by Maciek Szymanski » Sun Apr 05, 2020 12:10 pm

That’s very interesting idea. I’m looking forward for the results.
The peripheral holes in the cathode makes sense for me. As the most of the ionization in the discharge is done in the cathode region by the secondary electrons the central solid portion works as a target for ions and secondary electron generation. Of course these ions will be lost for the fusor, but the anode-cathode discharge current is the “engine” producing ions. some of them will pass through the holes and will be extracted by the main fusor cathode. For other hand I doubt if the needle type anode will do any help. The main function of the anode is collecting electrons and repelling ions in the positive column so to my humble opinion the flat plate may perform better. But as always the experiment will give the answer.
Also looking at the photo of those electrostatic ion guns I’m wondering if the black rings are the ferrite magnets for improving ionization?
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Dan Knapp
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Re: Fusor V construction - the process long running

Post by Dan Knapp » Sun Apr 05, 2020 7:54 pm

If you need a way to make really sharp tungsten tips, I suggest using the electrochemical etching method used to make scanning tunneling microscopy probes. I used this approach when I tried to make a sharp focus cold cathode electron source. I wasn't able to get the electron current I was seeking, but I did manage to make some very fine points. The method is the following:
I used 0.020 inch tungsten welding electrodes with 2% cerium. The points were electrochemically etched in 2 molar sodium hydroxide solution using 4.0 VDC at about 20 mA. The tungsten rod is the anode, and a carbon rod is used for the cathode. The trick is make the etching occur only at the water air interface. You insulate the end of the tungsten rod (I used teflon insulation stripped from insulated wire) and then support the rod hanging into the etching solution with only about a millimeter of the rod above the insulation wetted. The etching takes place at the air solution interface until the bottom insulated section of tungsten drops off. You have to watch it and immediately turn off the current when the tungsten end falls off; contineed etching will eat away your point. The photo below shows one of these tips.
W tip.JPG
W tip.JPG (231.37 KiB) Viewed 3099 times

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Richard Hull
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Re: Fusor V construction - the process long running

Post by Richard Hull » Sun Apr 05, 2020 9:09 pm

The second drawing ( circles) is not related to the ion gun at all.. it is a totally separate idea for field emission ionization at the two conflat end plates to create local ionization in that desired region.

The first drawing is the gun by itself. Yes, a magnet (premanent or coil) could be slipped over the gun to aid ionization. There is nothing to prevent a filament replacing the needle in the gun. Tests would be needed to show any results. These are the only reasons I am giving the cross any chance at all in my future.

I did just about quadruple my fusion rate to over 500 counts per minute last night as I approached 30 kV, but arcing stem-to-sharp edge of the cross juncture to ball stem foiled any increase. I will have to alumina tube the thing, I guess to see if that improves things. I would typically get 50,000 cpm at the mega n/s mark with fusor IV using the identical 3He system.

Finally, hyper fine points would be ablated away instantly as they would become incandescent due to the current and round off, to become a W deposition source.

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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