Progress on my first fusor project

[Drew Scott]

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.

[Dennis P Brown]

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.

[Mark Rowley]

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

[Drew Scott]

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?

[Mark Rowley]

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

[Drew Scott]

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.

[Drew Scott]

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.

[Dennis P Brown]

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.

[Drew Scott]

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.