Budget and Insulator Questions

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Ben_Barnett
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Budget and Insulator Questions

Post by Ben_Barnett » Thu Sep 27, 2018 1:36 am

Hello everyone,

Budget question:
I am an undergraduate student considering building a demo fusor as a research project with a professor that will run 2 semesters, within a budget of $2000. From what I have read, this is reasonable given adept hands-on ability and scrounging around for components for cheap. However... as a university student I do not have access to a lot of the machining tools necessary to assemble a cheap DIY solution. I looked into the 2 SS half spheres spherical chamber approach and it seems too intensive for what I am able to do. I could outsource work to a local machine shop but it would be pay by hour.

As far as buying parts right off, my results from a preliminary CAD model using a 6" OD 3-way Tee assembly runs to be almost $50 right under $2000.
(This is capped off both sides with zero-length reducers, terminating with a 2.75" viewport and 2.75" HV feedthrough respectively. The open flange will go to a vacuum pump.)
Obviously this won't do as the gaskets, bolts, insulator standoff, wire grids, deuterium gas, camera, etc all will cost money.
section_view_fusor.png
Is this a feasible project or should I back out while I can? I am determined but I am also no fool. I know many here have been constructing fusors for years.

Insulator question:
Regarding the insulator, I am unsure how to approach this. In my design I have a HV feedthrough but would somehow have to protect the ~2kV power for a length of 3" to terminate at the inner grid. How should I go about this?

Thanks,
Ben

Dan Knapp
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Re: Budget and Insulator Questions

Post by Dan Knapp » Thu Sep 27, 2018 4:26 am

Ben
I see from your introduction that you are an undergraduate electrical engineering student, but I don’t know the nature of your university. If you are on a research university campus, there could be sufficient opportunities to scrounge or borrow needed items to get to a working system in a year. If yours is a primarily teaching campus with not a lot of hardware around, such opportunities could be slim. If you have to buy everything, and are on a time schedule such that you can’t wait for bargains to appear on eBay, your $2000 budget won’t be adequate to get to a working system given that you will need a high vacuum system (chamber with pumps, HV feedthrough, viewport, and gauges), an adequately powered high voltage power supply, a gas delivery system, deuterium, and a neutron detection system. Even given the worst case situation, I would urge you not to bail out. You could learn a lot in the pursuit even if you do not reach fusion capability in your one year pursuit. Consider the possibility of starting a longer term project that could be picked up by a future student(or students) to carry further. If that does not appeal to you, consider doing a project doing computer simulations of fusor systems. You can explore a lot of designs much faster than actually building and testing them, but keep in mind that you can do a lot of things in a computer simulation that may not actually be doable in real world hardware (e.g. using electric fields between electrodes that exceed breakdown levels in the real world).

Edit - I just reread your post and realized you said “demo” fusor. If your goal is just to light up a plasma in a year with a $2000 budget, you should be able to achieve this given some creativity. You don’t need a conflat flanged chamber just to make plasma.

ian_krase
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Re: Budget and Insulator Questions

Post by ian_krase » Thu Sep 27, 2018 5:42 am

You may not need to insulate the stalk inside your fusor - Paschen's Law is a funny thing. I didn't in my very rudimentary demo fusor If you do, you can buy alumina ceramic tubing or "fish spine" beads from McMaster. Not too costly. Or even use kapton tape (very cheap dirty solution).

You can use KF50 or ISO flanges rather than conflats. 6 inches is quite large for a pipe tee fusor, most are half that size or less.

On a university campus with significant research or engineering stuff there's almost guaranteed to be a machine shop. Even if you can't get access to that you might make friends with somebody who does. Alternatively I made much vacuum Hardware in cheap dirty fashion using a drill, Dremel, hacksaw, files, hole saws, a borrowed drill press, angle grinder, Mapp Gas blowtorch, and silver brazing rod. This provides a way to convert cheap castoff surplus vacuum assemblies of wierd shape into functional Chambers using cheap tools.

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Dennis P Brown
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Re: Budget and Insulator Questions

Post by Dennis P Brown » Thu Sep 27, 2018 9:28 am

All the above posts are excellent advice; however, a better approach is to use a four way cross vacuum connection rather than a three way. In this manner, you can more easily upgrade to a real fusor later if the extra equipment becomes available.

Also, consider that instead of building a demo fusor, rather build a viable neutron detector using an inexpensive russian He-3 tube. That is an excellent electronics project. Later, after that is complete, then maybe build a real fusor since being at the college/university, buying deuterium gas in a lecture bottle through the school could be done. I bet finding a viable power supply wouldn't be too difficult at the school.

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Richard Hull
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Re: Budget and Insulator Questions

Post by Richard Hull » Thu Sep 27, 2018 4:56 pm

All this goes back to the original discussion. "Am I just going for a demo only fusor and never beyond that?" If so, you can do it on the very cheap and it will function flawlessly and look like a kluge. If, instead, you are still interested in a demo device to show and reuse a lot year after year, you might want a more presentable model of the demo fusor. This will cost you a bit more in the form of a conflat Tee or Cross with a view window,etc.

Used professional conflat Tees and crosses show up at bargain prices on e-bay and with a bit of luck and ingenuity, I would think a simple minimalist, but good looking fusor pro-demo might be built for $1000. such an effort would make a college proud to have students study plasma dynamics, gas vs. pressure vs. voltage and current.

The added benefit of the more professional looking demo device is that you might just have the bug bite deep once you see star mode in a plasma and decide to move on to fusion. If so, and you have a pro-demo system, you are already well on your way to just bolting on some key add-ons and you can do real 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.

Robert Dwyer
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Re: Budget and Insulator Questions

Post by Robert Dwyer » Fri Sep 28, 2018 3:05 am

If you are on a campus that is doing research that requires vacuum equipment, almost certainly you can find a professor that knows of a storage cabinet that contains spare gauges, flanges, pumps etc... I was AMAZED at what I have found laying around in old storage closets at my university, under piles of scrap metal, and in old cabinets. Tings like turbopumps the size of garbage cans, big Alcatel workhouse roughing pumps, Pirani gauges, MFCs, old Maxwell Shiva style 20kj capacitors....

Talk to faculty and staff see if they have anything. If you are partnering with a research professor that will also boost their confidence in you, perhaps make them more willing to aid you or give you leads on where to find equipment for cheap. Check out surplus stores. They often get stuff that Ebay never sees (you can waste hours just gawking at their inventories).

Also, things like 4-way 2.75" ConFlats can be found on ebay or other vendors for cheap nowadays. I bought my viewport and gas feedthrough for a total $60. They were form the same seller so I just asked them whether or not they could lower the price if I bought them both instead of individually. Sure enough.. they went for it. If you are just looking for a glow discharge than more traditional style 'demo fusors' using a pyrex cylinder can be had. If you want the experience with proper vacuum equipment and measurement, or are hoping to do fusion in the future, ConFlat crosses can work just fine.

Good scrounging is an art form. One that comes with experience. Patience is key, as well at networking. Good luck!
If we throw more money at it, it will have to work... right?

Ben_Barnett
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Re: Budget and Insulator Questions

Post by Ben_Barnett » Sat Sep 29, 2018 7:12 pm

Everyone,

Thank you all for the experienced replies and encouragement. It means a lot to know everyone here is so passionate to help.

Dan and Robert, good scrounging definitely is an art form so I will start asking around as soon as I get confirmation of research funding. Hopefully, I will find at least a few useful items. I will also try checking surplus and Ebay, although I had little luck finding any of this on Nebraska Surplus Sales. There is a machine shop on campus but they charge per hour so modifications can likely be done by them if necessary, I will have to try calling in some favors.

I indeed plan to only build a demo fusor at this point due my experience, the short one school-year time scale I am on, and most importantly, the absolute Hades I'd be in building a radioactive/neutron source on campus without documentation. (Getting that documentation is a real stick too.) To answer Richard's question, I am planning to go for presentation of this device, which I why I opted for a ConFlat setup. In a year, after building and testing it, either someone is going to come behind me and keep on (maybe take it to fusion), or it will be given to the Physics or Engineering departments for display.
A live display would be really cool but hard to achieve. Perhaps it would be the chamber and an accompanying video... but back to point.

As both Dennis and Ian pointed out, 6" is a large size for a 4-way or tee.
My research proposal involved the idea of changing the inner and outer grid geometries to observe effects and I thought I would need such a size in order to fit the inner and outer grid inside the chamber. Perhaps this was a faulty assumption? No point buying such a large 4-way or tee if one that is half the size will do. I assume with both the inner and outer grids internal to the fusor, the vacuum chamber is grounded...

I will wait and see if insulation is required. If it is, I can buy some fish spine beads perhaps, as Ian suggests.

The hope is for a "quick" build so I can get right into the physics and optimization of those plasma dynamics.
The good news is that my research professor has a sufficient voltage supply and a vacuum pump, ridding the project of some additional issues others have had to face.

Ben

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Richard Hull
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Re: Budget and Insulator Questions

Post by Richard Hull » Sat Sep 29, 2018 7:34 pm

It is found that the outer grid is not needed in a Tee or cross conflat for the small plasma ball to form within the central grid. The spherical device is just for more uniformity of field and of the classic design type.

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.

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