Fusor Plan

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Pablo Llaguno
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Fusor Plan

Post by Pablo Llaguno » Tue Jul 24, 2018 6:18 pm

So for my plan to build a neutron producing fusor I've been designing a CAD and looking around for ideas on what would be the best approach for me. Basically what limits my project is the budget, so I am looking to streamline as much as I can but also having a system that will work. Here is what I have in mind.

Image

Image
Sorry for the quality of the renders, but I have attached the STEP file if anyone wants to see it more detailed in a CAD software.

So in theory, my system would consist of a chamber made up of a KF50 to KF16 reducing tee, which would have a brazed KF25 nipple for the viewport. The vacuum system would consist of a diffusion pump (which has been very difficult to source at eBay) connected to a machined adapter to a KF16 nipple, which would be connected to a KF16 right angle bellows valve connected to a KF16 tee which would house my vacuum transducer (MKS901p) and then the final connection to the KF16 of the chamber. The chamber electrical connection will be made by a KF50 compression fitting, similar to Liam David's DIY feedthrough. While not in the CAD, there will be a Swagelok fitting (1/4"?) for the gas supply. Finally, I will blank the remaining KF50 port, though I put a viewport in the CAD just for the sake of it.

What I am worried about are basically these things: (but if anyone sees another problem go ahead and please point it out)
  • Brazing: I've talked with some members, and they assure me that brazing small KF fitting isn't difficult with some practice and can get me leak-free joints. I am planning on just brazing the KF25 half nipple for the viewport, is it a good idea?
  • Viewport: I am also planning to save some money in the viewport, so instead of buying a $100 viewport, I am thinking of using a KF25 bored weld flange ( https://www.ldsvacuumshopper.com/1boresize.html ) and then using some epoxy or JB weld to place a 1" disc of borosilicate glass.
  • Feedthrough: the design I am after is the one Liam David made for his fusor, but I am worried that it may be overkill/overpriced because alumina tubes are expensive, could a spark plug or a glass disc feedthrough work for fusing levels of HV (+30 kV)?
    Here are some cutaway images of the feedthrough:
    Image
    Image
    Image
    /Credit for these pictures goes to Liam David, thanks for the help!
  • Diffusion Pump: Finally, I've been having problems looking for some equipment, and looking for a well priced diffusion pump has been a problem. I've been thinking of even going the DIY route, but if anyone has a recommendation here it will be greatly appreciated.
So that's all for me as of now, I just want to hear people's opinions/recommendations before I start buying things. I am still a long way off and need to solve some other problems like the electric, gas and detection systems, but getting a good start with the chamber would greatly help my voyage to fusion.

Fusor KF50 Reducing Tee.zip
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ian_krase
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Re: Fusor Plan

Post by ian_krase » Wed Jul 25, 2018 4:42 am

1. It looks like you have a pretty narrow pipe between the diffpump and the chamber.

Diffusion pumps are the large diameters that they are for a reason, and the valve doesn't help. This may make initial pumpdown a lot slower. (That isn't to say this is a showstopper by any means, just that it's less favorable).

2. Your drawing has the ceramic tube for the feedthrough going into normal Swagelok fittings. To make sure you know, you actually need to replace some of the ferrules with rubber O-rings or something -- the ferrules cannot bite into hard, brittle ceramics.

3. For safety I highly recommend making the connection of the HV supply wire to the top of your feedthrough as secure as humanly possible.

4. I don't think spark plugs are suitable, and almost all of them have resistors (built-in ballast?). Glass disks just seem risky --- though maybe glass pipe might be an alternative to alumina pipe.

Pablo Llaguno
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Re: Fusor Plan

Post by Pablo Llaguno » Wed Jul 25, 2018 7:41 pm

Thanks for the input Ian,

I planned a narrow pipe because operating a small chamber with big pipes/valves would make balancing the pressure very difficult, and thus with a narrower pipe, it may be easier to balance the pressure in the chamber.
3. Is very true, maybe I could rig something up to avoid the HV supply wire getting where it isn't supposed to; alternatively, I could put the feedthrough in the lower flange.
As for the feedthrough, for the moment I have been using a sparkplug for my demo fusor but it only handles the NST HV, so I am not sure if it will be enough for +30kV.
Last edited by Pablo Llaguno on Thu Jul 26, 2018 7:34 am, edited 1 time in total.

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Richard Hull
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Re: Fusor Plan

Post by Richard Hull » Thu Jul 26, 2018 5:43 am

Pablo,
Please do not re-quote what is in the post immediately above in a thread. Everyone has read it already. We just do not quote unless it from another thread entirely. We have to constantly re-iterate this as a lot of folks love to re-quote, but this is something we despise. We are capable of reading all posts in the thread, taking it all in and do not need a refresher quote.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Pablo Llaguno
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Re: Fusor Plan

Post by Pablo Llaguno » Thu Jul 26, 2018 7:35 am

Thanks Richard, I corrected it.

Any input on my plan? It would be very valuable.

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Richard Hull
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Re: Fusor Plan

Post by Richard Hull » Thu Jul 26, 2018 1:14 pm

I think the insulator will fail as shown. The length is great, (actually a bit too long), but wasted as the body diameter is too small if you plan to reach fusion voltages needed for easy detection of fusion.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Pablo Llaguno
Posts: 60
Joined: Sun Feb 05, 2017 11:00 pm
Real name: Pablo Llaguno

Re: Fusor Plan

Post by Pablo Llaguno » Thu Jul 26, 2018 8:58 pm

The insulator consists of 4 ceramic tubes: 3/4", 1/2", 1/4" and 0.187" respectively. With the 1/2" alumina tube telescoping inside the 3/4" tube, the wall thickness should be 1/4" along the whole length, and at the end where the other ceramic tubes telescope wall thickness should be even thicker.

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Richard Hull
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Re: Fusor Plan

Post by Richard Hull » Thu Jul 26, 2018 9:04 pm

As we always say, build it and report back to us.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

ian_krase
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Re: Fusor Plan

Post by ian_krase » Fri Jul 27, 2018 5:32 am

You want to be careful with stuff like that; in some cases the voltage will first blow through one layer of insulation and then blow through the other. Still it is worth a test.

This kinda reminds me of a design by Thomas Rapp where the feedthrough was "hollow" (a tube exposed to air on the outside, i.e. the air jutted into the fusor and inside the air in the tube was a cable insulated to 50 KV so it was already known to be good. You could imitate that.


Don't forget field control.

Pablo Llaguno
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Re: Fusor Plan

Post by Pablo Llaguno » Fri Aug 03, 2018 6:26 pm

That would indeed be a good idea, and I would only need one alumina tube. What other alternatives could I have as feedthroughs?

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