Fusor Forums

I wanted to have a thread for my project as it progresses. This is my first time trying to build a fusor. I am initially going with a similar design to the Makezine model to use as a demo fusor in my science classroom. Once I get that working well I would like to build a second model intended to actually perform fusion. My biggest hurdle here is available funds. As a public school teacher, these are somewhat limited. So this may be a long-term project, but sometimes the best ones are. I will update this thread only as I get things completed.

Enclosure minus the glass and gasket, The feet are made out of Delrin bar, with 1 inch aluminum top and bottom plate. Grid electrode prior to TIG welding (Stainless Steel TIG rod) The grid electrode after welding. My brother did this for me as he is a much better welder than I am and has access to equipment that I do not. He said the TIG approach did not work well for some reason so he used stainless steel MIG wire instead and spot MIGed it. I still have to clean up the welds and attach it to the bolt that will go into the HV feed through.

A demo fusor is a great starting point while you slowly work up to some better equipment. For anyone with small funds, their best ally is time and patience. Check ebay regularly and for some items set up a notification when things get posted.

Knowing your way around electronics is an indispensable skill. I have found some killer deals on parts that were labeled as 'broken' but only needed a switch replaced or something. Tricky though knowing whether a broken part is truly broken or just labelled as such, never want to waste any of the precious funds.

Anyways, good luck on your efforts!
Quaid

A proper vacuum system is the first major sub-system in building for any demo or future fusor. A proper two stage vacuum pump, proper connectors and a micron level gauge are essential. The nice thing about a good vacuum system is that far more can be done with that basic system than just building a fusor. So building a good vacuum system is both useful and a great first learning experience.

Once I get the fusor chamber somewhat assembled (should be within a week) the vacuum system is my next sub-project! It just so happened that I had easier (and less expensive) access to the materials for the fusor chamber itself first. Maybe some Xmas money will help me along! (Just kidding, who gets Xmas money at 35!? But hey, you never know...)

By the way, what else CAN I do with the vacuum system?

A simple vacuum system can be used to sputter metals onto glass - I did this as a high school student. It can also be used to create plasma glows in tubes - like observing Cook's dark space (of course both these processes require a cheap power supply of a few hundred volts. But those are very cheap and available on ebay.) Most materials will melt at lower temps under vacuum. One can freeze dry specimens/foods under vacuum. If you want to create an ion gun or small low power accelerator the vacuum system is essential. One can use such a system (there is a nice Sci. Am. Amature Scientist piece on this) to liquify some gases or create very cold chambers (again, I did this in H.S. and got to -50C.) One could empty a glass tube, place a feather in it and show that it falls with no air resistance just as fast as a lead shot. A basic vacuum system combined with a high vac pump (i.e. diffusion pump or turbo) can be used to do metal vapor deposition onto glass. Or create a higher power accelerator.

The basic vacuum system is the heart of that more advanced system. And since for a fusor, of course, such a system is required but one must first start with the simple two stage pump and related plumbing/gauges.)

There are a number of more exotic applications one can find besides these - with a NST one could build a very powerful (a few watts) CO2 laser (again, did this in H.S.) Again, the old Sci. Am Amature Scientist has a number of projects that require vacuum systems. All require a basic system - there are other applications but this should paint a picture. Yes, one needs to add various extra parts but all these applications require that basic system.

A basic vacuum system and gas management system can also be used to make gaseous radiation detectors. With a pump that could reach about 10 microns you should be able to avoid the worse effects of electron attachment created by oxygen residue. Backfill this with a P10 mixture (commonly available) through a pressure reducer and you can have either a proportional or Geiger tube by operating the contraction at different pressures.
Richard had various posts about homemade Geiger tubes, and all this is explained in various books (Electron and Nuclear Counters by Korff most prominently)

Here is my high voltage feed through. It began as a 6" long by 0.75" diameter ceramic tube. The stainless steel standoff was only 4" long, so I had to cut 2" off the tube. I underestimated how hard this ceramic was. The only diamond cutting device I had was a diamond concrete saw blade for my skilsaw. Well it worked, though not a perfectly clean cut as you can see in the piece that was cut off in the background. After cutting, I ground the hex edges of the stand off down just a bit and epoxied it in the tube, taping over the threaded holes to keep epoxy out of the threads. Next step is to epoxy the feed through into the bottom plate!

Good luck with your home brew feed through. Did you get the expensive machine able ceramic?

I used this one: https://www.mcmaster.com/8746K575/

The feed-thru needs to be vacuum tight; so getting epoxy to seal well is critical; also, these electrode tend to get rather hot so use a grade of epoxy that can handle that.

I used Devcon 5-minute epoxy (https://www.amazon.com/Devcon-Epoxy-Min ... B005JZVJMO). I hope it works well. If it doesn't, well, that will be a learning experience. I try to plan things out and not be impulsive or impatient with my projects, but that doesn't always happen and sometimes I learn best after doing things wrong the first time. Anyhow, we will see!

I still have yet to glue the feedthrough into my lower plate. Any recommendations as to what kind of epoxy I should use for that, assuming what I used above is no good?

EDIT: I found this in the reviews: "Minimum to maximum operating temperatures are -40 F to +200 F"

So maybe this isn't such a great one to use. I guess I will try it anyway and see. Maybe just for short runs, it is just a demo fusor anyway for classroom demonstrations. I will keep this all in mind when I get ready to build my real fusor, but at that point it will be a different design anyway and might not use any epoxy.
Not glued in yet, but fits nice and tight. I bought some high temp silicone gasket maker. I was thinking of using that to seal the gap around the perimeter of the ceramic tube, then some titanium epoxy putty as a cap of sorts over the gap. I could also make a cap with the titanium epoxy putty at the end of the tube to seal off the inner diameter as well.
All assembled, though not permanently. Still have to seal the feed through in. Glass and gaskets should arrive this week. Then all that will be left is the high voltage and vacuum systems. Already have the NST and HV diodes, just have to build the supply with them and then fork up the cash for a vacuum pump and gauge.

A demo using a NST shouldn't get too hot - that metal plate should keep the seal at the ceramic/metal interface stable with its large heat capacity and cooling area. One thing I'd suggest is don't use multiple layers of different materials to seal the feed-thru. The differntial thermal expansions rates tend to create more issues. Be certain the surfaces are very clean - use alcohol to clean the pieces before expoxy is applied.

Looking good!
The key is to not have the epoxy in anyway directly exposed to plasma. If plasma gets close or touches it, outgassing, burning, carbonizing, etc will become a big problem.

How long is the insulator on the other side of the plate?

Mark Rowley

Thanks!

It's hard to tell in this pic because it sank down since it isn't glued in, but the feed through is 4" long and the plate is 1" thick, so when I center it and glue it, it should extend 1.5" to either side of the plate.

When you say the epoxy shouldn't be exposed to the plasma, do you mean not exposed to the vacuum at all, or just the part where the plasma concentration is higher or visible? What is the best way to achieve that? I have added a stainless steel nut and washer below the grid and above the epoxy line kind of as a cap. Would that protect it enough you think?

A washer and nut should protect it fine. I wouldn’t attempt any re-do at this point.

If you were ever to make another, it’s best to only fill the ceramic tube 25 - 50%. That would be more than strong enough to support the center conductor. The open half would be in the fusor and the part where the epoxy is flush with the bottom would be on the outside where you connect your HV cable.

It’s a general practice to not have directly exposed epoxy in the vacuum chamber. If it’s covered, protected, and at a thermally inconsequential distance you’d be ok. -Demo fusor only-

Mark Rowley

Excellent advice, thanks!

I will try it and if it doesn't work great I will redo at that point.

Better image of progress so far. You can see my two Tesla coils in the background.

Everything but the glass and gasket. Since this is a demo fusor, I may have to try it without a vacuum gauge at first until I can find one I can afford. But I do plan on adding one soon. Next up, I need a vacuum pump.

The cost of large diameter and long glass cylinders is rather up there - especially the thick glass you will need for safety; also, a plastic housing will be needed if you want to operate in a school environment. Pumps (on ebay) can be cheap if one waits for deals.

I found rather inexpensive vacuum stuff on ebay and one piece made a nice chamber; I just needed a glass plate 8" across for one face. A telescope blank worked great and the price was reasonable.

Also, try to rotate your pics so they are corret when posted.

I have the glass ordered already, just waiting on it to get here. I ordered 2 just in case. Borosilicate tube, flame polished ends, 6"h x 5"dia x 0.196" thick. I'm not sure why the images are sideways, if you click on them and enlarge them they show up correctly orientated. It may have something to do with uploading from my phone.