Lithium vapor injected into fusor with deuterium fusion initiation.

For posts specifically relating to fusor design, construction, and operation.
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Carl Willis
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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by Carl Willis » Tue Feb 24, 2009 11:13 pm

Hi Rick,

You can make significant numbers of neutrons with common alpha sources and pieces of beryllium, and you can do activation, inelastic scattering, and other experiments with those neutrons. My AmBe source is mentioned here (although certain details are purposefully concealed to help prevent little problems for me).

http://carlwillis.wordpress.com/2008/07 ... on-source/

A couple other people on this forum have similar things. They are rarely discussed in full detail. The alpha emitter can be Po-210 from antistatic brushes as well. A healthy amateur AmBe source can produce a few thousand neutrons per second.

>the stand off distance should be less then 39 mm

Much less (unless done under vacuum). The yield of Be-9(a,n) is strongly dependent on energy. You want the alpha particles to arrive in the beryllium with the maximum possible energy, and that means effectively no air attenuation is tolerable.

-Carl
Carl Willis
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Lithium trick
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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by Lithium trick » Wed Feb 25, 2009 1:34 am

Carl,

Thanks for the info about your website, a well done site it is. I knew about the vacuum, but I don't want to give out too much info for the same reasons you did not say more about your device. I consider any info we can share here or else where to be purely a topic of interest and of scientific interest at that. As a laser engineer and applications specialist, I am always interested in the applications end of physics. I get to laser cut all kinds of things people tell me one cannot cut, like 2.5 inch think glass filled concrete, granite, and I have never found a material that cannot be laser cut save for soda glass, and automotive safety glass. That is not saying I would cut alloys that are hazardous, such as beryllium alloys, Brass I don't like because of the zinc and zinc plated steels, and some types of plastics as they are not healthy for humans to be around when vaporized. Copper is a tough one to cut.

I always check the MSDS on all material safety for the process. In some cases water jets are the safest tool for the job. In others a conventional hard tool such as a milling machine.
I would like to assist others with their efforts to make suitable grids for their home made fusor's, as some day I would like to build one of my own. Laser cut grids are the answer for an accurate and durable and reproducible grid. The people at NSD Fusion do have what appears to be a very respectable and durable Fusor design. All are welcome to share.

Any idea's on a wave guided neutron design, Teller did it, so it is possible, proper shielding and neutron transparent and reflective materials would be my guess of where to start.

Good day sir!

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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by gamempire » Wed Feb 25, 2009 1:42 am

Rick,

I agree that laser cut grids are the way to go. I've attached a picture of the first grid I made last April.
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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by Lithium trick » Wed Feb 25, 2009 2:19 am

Stainless steel? What about using more segments in the design as well.

One should check out Unitednuclear.com

Uranium Ore samples, and Receiver tubes for home made Xray machines, and other cool stuff. Lithium, and Beryllium sources.

Got to run...

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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by Lithium trick » Wed Feb 25, 2009 4:17 am

Josh, how did it work for you? Do you have any recommendations on the diameters of these grid pieces. As you know they can easily be made to about any size needed, What about the inner grid? And what material did you use?

I can get time in a shop to make many of these, and TIG weld them up as well. How about the electrical hook ups? Maybe even electro polish and passivate them. I have a pretty good idea on how to do this, But it's nice to see what worked and what can be improved on. I can get vacuum fittings easy enough.

Richard Hull should know this stuff, Any ideas Richard?

Rick

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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by gamempire » Wed Feb 25, 2009 7:12 am

For the grid in the picture, I used 316 stainless, .055" thick. I cut 3 rings with notches in them. I've attached a drawing I did for inclusion in a report.

The only way I've managed to make an electrical connection is welding a piece of SS rod (1/8" works) to one of the joins on the electrode. I then made a barrel connector with 2 set screws, one connects to the rod on the HV feedthrough, the other to the rod coming off the electrode. I'll try and take some pictures of it tomorrow if I have time.

I actually would like to figure out a way to modify the grid to old a small disc to use as a target. Maybe you can work some wizardry for that (I can provide the Autocad files for the current grid).

Richard did some research on different types of electrodes, I remember reading about the Tungsten tip electrode on the forum somewhere. Even if you made a grid out of tungsten wire, I don't think it would be such a great choice. Even though it can withstand a ton of heat, the resistivity of it the metal makes it a very unfavorable when you have alot of power going through it (try putting 500 or 1000 watts through a tungsten filament from a lightbulb, or some tungsten wire the same size as other wire used in grids, and you'll see what I mean).

Also, you probably don't need to electropolish it even when cut on the laser cutter. Any rough edges were sanded down, and after about an hour in a helium plasma, the grid completely stopped arcing from any microscopic edges.
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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by Lithium trick » Wed Feb 25, 2009 3:38 pm

I can easily create such DXF files and in fact I have stated to do so even before your reply posting. I will add in the slots simply to make assembly a snap, literally. With a few tack welds it would be done. Tungsten is durable, but due to it's lack of ductility and brittleness and resistance electrically, it has some issues that make it a poor choice for such work. I use nitrogen as the assist gas to laser cut the stainless steel, so the edges will be clean.

I have lots of options on the electrode hook ups, the one issue to be resolved is the insulation between the incoming electrode wire and the chamber walls. I suggest a Aluminum Oxide ceramic tube of the right size ID and OD to fit into a vacuum fitting, such as an ultra torr fitting made by a company who specializes in such vacuum fittings, Cajon, and/or a Parker vacuum fitting product come to mind. View ports are available from the same companies suitable for vacuum applications. What is the operating pressure so as to select the pump? I assume some where around 10 to 40 microns of pressure? A Diffusion pump along with a mechanical 2 stage roughing pump might be over kill, but? Home made Deuterium made from heavy water and seems possible enough via electrolysis of D2O and a dissicant to dry it. With my practical applications experience in building such vacuum systems, it would be easy for me at least to build such a chamber, complete with vacuum instrumentation and vacuum pump controllers. Neutron detection components would have to be sought out, but all are possible given enough time and money and scrounging around, it could and can be done, obviously.

Any input from others would be appreciated. I assume your idea of a solid core target could be a lithium source? It does seem to be an interesting idea. Of course lithium is a hazardous metal to work with as you know. Other then that I have no clue as to what your solid target could be, or the end goal of such development. More details please, perhaps a DXF file of your flat work on the grid would be useful, the three d model is useful conceptually, but a flat work DXF file is what I need to laser cut such grids. My laser posting software requires such a file format to generate the CNC files for the machine tool and would save me some time as well.

Rick

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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by Lithium trick » Wed Feb 25, 2009 8:33 pm

Josh here is my copy of a bit map file of the flat patterns I worked up. I have created them in DXF format for my laser programming software, minus dimensions as they are not needed to program the parts. I am not going to use a cutter compensation as it won't be needed. The beam when focused is only .008" in diameter, so this will cut the geometry will split the tool diameter in half. This way I'll have the little bit wiggle room afforded for assembly, and tack weld the pieces together by way of TIG welding.

Any thoughts on a inner grid design and I can work out the rest, as well as the target within the inner grid. I assume this target will not be electrically charged. Simply in the focus of poissan (sp?).

I attempted to send a copy of the BMP file I have but for some reason it wouldn't show on the website.

Rick.

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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by David D Speck MD » Wed Feb 25, 2009 8:50 pm

Josh,

I think that the resistivity of the tungsten wire would not be a significant factor in fusor design. You may be pumping 500 watts into the fusor, but it is being delivered as 33 mA at 15,000 volts or so.

Resistive power losses are measured as I Squared R. That's why long distance power transmission is done at high voltages. Only the current carried, and the resistance of the wire matter in power loss (at least till you get into corona losses!). Jacking the voltage lets you deliver more power without increasing the I^2 R losses.

Even if your tungsten grid element had a resistance of 100 ohms from one end to the other (a pretty high estimate for a decently thick piece of tungsten wire strong enough to be self-supporting), the resistive power loss in the grid element (assuming all the current passed through a single grid conductor) would be only (0.033^2) * 100, or 0.1089 watts, an insignificant loss. In reality, the loss would be even less, as most grid assemblies are a continuous loop, and most grids have at least 3 loops, which would cut the resistance by a factor of 6.

Therefore, you could make your grid out of nearly any conductor. As I understand it, the major deciding factors are the ability of the grid to resist sputtering, and the effects of heating, softening, deformation, and melting due to electron bombardment. I thought I read once that aluminum was the metal most resistant to sputtering, but it certainly would have problems due to its low melting point. I have some tantalum wire put away for my "someday" fusor. Stainless steel is cheap and readily available, but I would think that tungsten might be better if you can find some surplus material that isn't too expensive.

Another issue is how you would be able to clean off the sputtering residue from the inside of your chamber, or from the windows. With some metals, you can just drop your windows into some hot acid to get them transparent again. If you get into exotic grid materials, it may be difficult to find an acid that will dissolve them effectively without attacking the windows.

Dave

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Re: Lithium vapor injected into fusor with deuterium fusion initiation.

Post by gamempire » Wed Feb 25, 2009 9:26 pm

Dave,

As my mind has been completely elsewhere the last couple weeks, I completely forgot to mention the sputtering issues. I thank you for doing so. Tungsten would definitely cause some severe sputtering issues. The only way we'll find better material for the electrodes is by experimenting though.

-Josh

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