Demo fusor first light

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Demo fusor first light

Postby Pablo Llaguno » Wed Mar 15, 2017 2:17 am

About two months ago I started looking for parts and getting ready to build a demo fusor. After some work, we, my team and I, were able to make our demo fusor, which was intended to be used as a science fair project, which was this last weekend and overall it worked very well.

In the video I will link below, you can see how we were able to create a purple plasma, needless to say, this "demo fusor" is not as good as lots I've seen here, but this is just a start and we hope to get better at it and in a few months be able to produce neutrons (I know it will take a lot of redesign). Obviously, this will take a lot of work and research, and I am sure I will find lots of info here.

Some things to note:
·We used a 15kV @ 30mA (rated) NST, we didn't use a voltage meter or current meter, but judging by a consumption chart and what most people say about NSTs, we probably are in the 7kV range or less.
·Our vacuum system wasn't very good, mainly because of our gauge, because we didn't have the funds at the time to get a nice thermocouple gauge, so this is something we will try to improve and hopefully we will be able to give some readings.
·Also is worth noting that in our video the plasma was purple because of possible leaks and not letting the vacuum pump enough time, in our science fair we let it pump for about 5 minutes and instead we got a blue almost white plasma and it was more confined. We will try to record that.
·Talking about our plasma, in our science fair our glass chamber suddenly turned black, possibly because we were producing a lot of heat, so we had to disassemble and clean (which was very difficult) but we managed to do it quickly. After this, we restricted the time our fusor was running.

And that's all! Hope you enjoy and any suggestion/comment/critic would be appreciated.

Link to video: https://www.youtube.com/watch?v=RCsls0o6kHI

Image
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Re: Demo fusor first light

Postby ian_krase » Wed Mar 15, 2017 5:21 am

My comments on this:

1. Don't forget the possibility of a Mini Convectron or MicroPirani gauge (make sure it's the version with the built in digital display!) which come up on Ebay routinely. These have the nice feature of working all the way from medium vacuum to atmospheric, and the full setup (used!) may be cheaper than a themocouple. It's what I use, anyway.



2. If you were able to get to the point where the plasma turned whitish, but it took a very long time (for a chamber that small), then it sounds like you have fewer leaks than I ever have had, but very slow pumping speed. That long, thin foreline may be the problem. With a chamber this small, you can possibly do what I do and bolt it to the top of your pump (make sure to use some kind of screen or horizontal run so nothing falls in if there's an accident).


I'm curious what you are using as a feedthrough.
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Re: Demo fusor first light

Postby Dennis P Brown » Wed Mar 15, 2017 2:28 pm

If the chamber turned black - that is a sure sign that either pump oil (back flow) or gasket material is being "burned" by the plasma. Until you have some type of working vacuum gauge, you will remain in the dark on possible leaks and performance of your vacuum pump/system. A vacuum gauge is rather critical to move forward in using your demo system.
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Re: Demo fusor first light

Postby Pablo Llaguno » Wed Mar 15, 2017 10:57 pm

Thanks for the comments/suggestions,
Yes we will look into a new gauge, those mini convectron gauges seem to be fairly common on ebay and not expensive, We just have to figure out what thread size/fitting we want. I am not familiar with ConFlat or KF, just with standard milimetric or NPT/UNF fittings, any suggestions or links to where I could learn about them? From what I read, a ConFlat works with an o-ring and an edge making pressure on it, which would mean I will need to machine/buy an adapter for my chamber, and in that case maybe I should probably make a new chamber anyways. What do you say?

Also yes plasma started purple, turned blue and then almost white but didn't took a lot of time. Something like 5 minutes or so. BTW our chamber's volume is 0.9 liter (something like 54 cubic inches) and since the vacuum pump was borrowed, we don't know the specs because the printings on it aren't visible anymore, but it is a robinair and looks like a two stage. In the CFM rating, I can barely see a 6.

We used a lawnmower sparkplug, cut a bit of the threads and then welded a #10 SS screw to it, which is welded to the grid.

As for leaks, we may have some in the seals, we are not to proud of them, and we are not even sure they work all that well. If we had the equipment, we could make a groove in each plate for an o-ring and it will probably seal way better, but in that case maybe we will just make a new chamber.

We did some leak testing with a nitrogen tank and filled the chamber to about 40psi (had to replace vacuum gauge with a pressure gauge) and checked for leaks with soppy water, we fixed the big ones at the fittings but not the ones around the rubber seal...
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Re: Demo fusor first light

Postby Pablo Llaguno » Wed Mar 15, 2017 10:59 pm

Dennis P Brown wrote:If the chamber turned black - that is a sure sign that either pump oil (back flow) or gasket material is being "burned" by the plasma. Until you have some type of working vacuum gauge, you will remain in the dark on possible leaks and performance of your vacuum pump/system. A vacuum gauge is rather critical to move forward in using your demo system.

It could be burning but the weird thing is that it turned black instantly just after a big blue arc appeared, so I think maybe we just run it for a very long time.
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Re: Demo fusor first light

Postby ian_krase » Thu Mar 16, 2017 5:32 am

A sudden "big blue arc" is... something going badly wrong, but I'm not sure what it would be, I'm afraid. Was your grid (and everything else) intact afterwards? What kind of arc was it?




Conflats don't use O-rings, although you can use O-rings or a special rubber gasket with them for quick temporary setups. They are expensive and use a soft copper "crush gasket" -- the knife-edge rings on conflats bite into the copper gasket, and you can generally only use the gasket once.

For a demo fusor, conflats are of questionable utility and I'm not sure if they are absolutely needed for a real fusor (can somebody more knowledgable chime in?). They also are large, bulky, heavy, and expensive. You will probably want to stay away from it for anything like a small gauge port.

VCR fittings are like tiny Conflats. Also very expensive and not really relevant for this.

I'd aim for a KF16, KF25, or NPT fitting. For gauges the 1/8 NPT seems common and is probably a good enough choice.

KF fittings, and their bigger brothers ISO flanges (sometimes ISO LF) are easier to work with since they use O-rings to seal (of course, this means that they are not very heat resistant). A cool thing is that you can buy solderable/brazable brass KF fittings and then use ordinary plumbing solder to connect them to copper tubing, which lets you build small assemblies cheaply.

Personally I wouldn't be too quick to throw much stuff out -- I can't quite see how your chamber is constructed -- but incremental improvements do a lot. Things will suddenly get much better when the last leak is sealed.


Do you have vacuum grease? If so, you can probably improve your chamber seals. Also, with a can of Dust-off you can probably do leak checks using a glow discharge -- it will abruptly change color (to paler and brighter) and get larger when you spray the gas around the leak. No need for a gauge with this trick (though it is nice to have). This will find lots of leaks that are not really visible with pressure and bubbles.
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Re: Demo fusor first light

Postby Pablo Llaguno » Mon Mar 20, 2017 9:16 pm

I am not sure if it was an arc or what was it, but what I do know is that it was like a flash and suddenly my chamber was black, maybe it was the heat from the plasma? Also regarding NPT fittings, do they work well enough even for a real fusor? And lastly, yes I did use vacuum grease, how can I improve that?
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Re: Demo fusor first light

Postby John Beutz » Tue Mar 21, 2017 2:47 am

Simple google search with the keywords "fusor" "NPT" and "vacuum" gives some good results.
viewtopic.php?f=10&t=4246

Your plasma looks a lot like my old demo fusor's. I found that a minimum amount of vacuum grease over the rubber gasket worked better than a slather. The black on the chamber might be burning rubber. Does your gasket extend into the chamber? Hard to tell without pictures.
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Re: Demo fusor first light

Postby Pablo Llaguno » Tue Mar 21, 2017 2:59 am

So for a real working fusor I would probably want KF fittings, thanks. Here is a picture of my chamber Image
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Re: Demo fusor first light

Postby John Beutz » Tue Mar 21, 2017 6:12 am

From what I've seen on the forums and with my experience with a much inferior pump, I bet with a pump like yours a KF chamber should get down to a couple dozen microns easy, even with a few NPTs. KF crosses and tees can be found on eBay for less than 100$
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