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

Posted: Tue Feb 24, 2009 6:13 pm
by Carl Willis
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

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

Posted: Tue Feb 24, 2009 8:34 pm
by Lithium trick
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!

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

Posted: Tue Feb 24, 2009 8:42 pm
by gamempire
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.

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

Posted: Tue Feb 24, 2009 9:19 pm
by Lithium trick
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...

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

Posted: Tue Feb 24, 2009 11:17 pm
by Lithium trick
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

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

Posted: Wed Feb 25, 2009 2:12 am
by gamempire
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.

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

Posted: Wed Feb 25, 2009 10:38 am
by Lithium trick
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

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

Posted: Wed Feb 25, 2009 3:33 pm
by Lithium trick
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.

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

Posted: Wed Feb 25, 2009 3:50 pm
by David D Speck MD
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

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

Posted: Wed Feb 25, 2009 4:26 pm
by gamempire
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

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

Posted: Wed Feb 25, 2009 4:56 pm
by gamempire
Attached is the DWG file for the design I posted.

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

Posted: Wed Feb 25, 2009 6:48 pm
by Lithium trick
Dave, We have not talked before, here on this forum, but here's a thought, a sacrifice disk/ cover glass, can be placed in front of the real window to take the sputtering contamination beating from burning in a grid. A simple solution as it's done very often for expensive laser lenses used in Laser cutting, they typically run around 15 bucks or so each in orders of 10 or more, and are made out of KaCl, as a expert in CO2 laser cutting I have seen them used many times commercially, saving my customers thousands of dollars a year as beginning operators during training tend to destroy the focus lens during their training months. I don't use them and have never needed to do so as I have 15 years of cutting behind me, so my training days are well behind me. I don't trash optics at all.

Many good acids will clean out a chamber as you pointed out. My thinking is though a inner grid would be worth exploring as it would collect the majority of contamination by way of electron flow to the inner grid. Would this not be true? Of course these devices do need a burn in period understandably to clean up the chamber and grids.

Rick

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

Posted: Wed Feb 25, 2009 7:15 pm
by David D Speck MD
Rick,

Thanks for the info. I had no idea that you could get optically clear KCl discs in that size so inexpensively. Any suggestions as to a source? Perhaps we could arrange a group buy to get past minimum quantity requirements.

I though I would just use discs of flat window glass, or Pyrex, if the ordinary glass shattered. I could probably turn off the system pretty fast if I saw a failure of the sacrificial window. Not sure where I'd find Pyrex discs, though.

Any reason to think that the KCl would have a significant advantage over Pyrex, especially since we're only using them as viewports, not as high power IR laser transmission windows?

Dave

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

Posted: Wed Feb 25, 2009 8:17 pm
by Lithium trick
Dave, Here's a tip.
lenssavers.com The company is International Crystal Laboratories. You can look on their web site for the lens saver product. They tend to be hydroscopic, so one must keep them dry, but the system would be under vacuum, by simply closing a valve at the vacuum pump to hold the vacuum while not running the system. Why waste time out gassing the system again unless you are doing internal maintenance? Pyrex blanks could be sourced from Edmonds optical, but I will warn you they are not a source I recommend as everything they sell is expensive as heck.

I, myself, would look around on the web for vacuum fitting companies, and in particular ask about view port windows, and shield windows for this application. I chose ICL simply as a cheap throw away heat tolerant window that I knew could be made to work. Many other options should work as well. No plastic though for obvious reasons. I would suggest a local scientific glass shop Weiss Scientific Glass in Portland, OR. Or Hayward Quartz in Hayward CA, both companies work with Quartz glass, and they can make these windows however I have no idea what they would cost. The whole deal depends or the size of your view port. So those are just a few idea's for suppliers. Certainly there are many options here. No need to waste a good view port window because of some contamination.

I'm still interested in the dual grid setup as originally designed, I have specific reasons for this choice.

Rick

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

Posted: Wed Feb 25, 2009 9:32 pm
by Lithium trick
Josh, I have downloaded a DWG reader.

I have also worked up my copy's of the Auto CAD file you posted and I have the math all worked out, I plan on cutting them out this week if I can get the machine time. It's just a couple of minutes on the machine, I'll cut one set, and check out the assembly. Then cut several sets just to have them around, I can get double insulated high voltage wire I use for laser repair, and the PFA tubing I use to triple insulate this wire, it's proven beyond 70,000 volts at WAY BEYOND the currant draw I could ever put through it. So the next step is the biggest hurdle, the vacuum system, by far this will be the biggest part and expense so far and the instrumentation to run it, and hold a set point A good set of idea on the grids I have posted already, it seems to me a long term issue for system performance and stability. The sputtering issues do concern me, I hope you find it useful. How well do the stainless steel ones work for you, and when do you start to see the sputtering problem show up at what voltage and what amperes? You indicated you had to burn out the cavity and grids for about three hours with helium, how is it now?

Rick

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

Posted: Wed Feb 25, 2009 9:48 pm
by Carl Willis
This thread seems to be treating a number of disparate topics at this point. It would be better, going forward, if individual topics were given their OWN threads or put in the appropriate existing threads. For instance:

- Josh's laser-cut grid and related discussion
- Optical windows and how to clean them
- Cold neutron beamlines
- Commercial neutron generators
- Be(a,n) neutron sources
- Lithium vapor and whatnot, previous thread located here (viewtopic.php?f=14&t=6731#p42414)

Some of these topics do not really even belong in Fusor Construction and Operation, but in the other forums.

The disadvantage to having long, multi-directional, Faulknerian stream-of-consciousness threads is that it defeats the site's organizational structure and makes it harder to search out material in the archives.

Thanks...

-Carl

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

Posted: Thu Feb 26, 2009 11:14 am
by Chris Bradley
I was at the point of posting similarly.

What *was* this thread about?

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

Posted: Thu Feb 26, 2009 2:16 pm
by gamempire
Carl Willis...bringing sanity back to the insanity