Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

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Maxwell_Epstein
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Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

I'm considering upgrading my demo fusor's vacuum chamber from a homemade vacuum chamber based on the design in Make Magazine with a steel high vacuum chamber. I found a supposedly decent one on eBay that is well within my budget and that I think will work well for my purposes (ideally, I'd like it to be future-proof as long as possible). The only potential issue is that the interior is rectangular instead of cylindrical as I have seen in most fusor chambers.

If I go for this chamber, what can I expect as potential issues? Will there be any problems with arcing due to the sharp edges? Does it matter whatsoever that it's square?

I would greatly appreciate any advice as I am very new to the world of industrial vacuum technology. Thanks!

(Attached is a picture of the chamber from the eBay listing)
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Here's an interior view of the chamber from the eBay listing
Here's an interior view of the chamber from the eBay listing
s-l400.jpg (17.23 KiB) Viewed 3229 times
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Dennis P Brown
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Dennis P Brown »

Hard to tell but you will need a number of ports so you can add a observation window, high voltage input, exhaust port, made a small inlet for deuterium gas. I cannot tell what ports that chamber offers nor its size. Having sufficient room to prevent serious arc overs is useful. I assume it has a cover plate of some type - that image would be useful as well.
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

Thanks for your response! I've attached all of the pictures from the eBay listing below as well as the eBay link.

I currently envision using the 4.5" port closest to the chamber (as opposed to the one at the end of the beam) for voltage feed-through to the grid, adapting the large 8" port down to a smaller one that connects to the vacuum system, and using the 4.5" port at the beam (is there a technical name for that?) as a viewport. I found a 20kV insulated feedthrough on a 1.33" flange that I could adapt the 4.5" port to (I should probably try to avoid adapting things a lot, though). It's rated for 30 amps, which makes me think that I'd be paying extra for something that I won't need. Is there a better option? I found a viewport (McMaster Carr: 3993N13) that I think will work, but would like to find something similar used if possible, do you have any suggestions?

I don't know very much about how this should go together and would greatly appreciate any advice. I've read through the FAQ, but am not sure exactly how to apply it to this chamber - or if using this chamber is even worth it. If there's a better option for an affordable UHV system that I've overlooked or if I'm coming at this from the wrong direction, please let me know. Thanks!

Vacuum chamber link: https://www.ebay.com/itm/224580355875
HV Feedthrough Link: https://www.accuglassproducts.com/cf-fe ... 133-flange
Attachments
square chamber 12.jpg
square chamber 11.jpg
square chamber 10.jpg
square chamber 9.jpg
square chamber 8.jpg
square chamber 7.jpg
square chamber 6.jpg
square chamber 5.jpg
square chamber 4.jpg
square chamber 3.jpg
square chamber 2.jpg
square chamber 1.jpg
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Liam David
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Liam David »

I don't think it would be in your best interests to go this route. While I'm sure this chamber could be made into a functional fusor, it's a rather awkward geometry and the ports are not ideal. I'd suggest going for a 2.75" (or 4.5") conflat 4- or 6-way cross chamber that I and a few others have had success with. It would be cheaper and easier to get everything like the viewport, feedthrough, etc. interfaced to it.

The feedthrough is rather small, especially on a 1.33" conflat. It would be fine for a demo fusor but not a neutron producing one. I have a post detailing the construction of an inexpensive, very high voltage feedthrough for <~$150 that you might want to take a look at. Otherwise I'd recommend one of the 30kV fluted feedthroughs on a 2.75" conflat that you often see used here.

Don't buy high vacuum products from McMaster as they are ludicrously expensive. Search for "conflat viewport" on Ebay.
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

Thanks for the advice! I'll check eBay for a chamber of the type you recommend (I think I've seen a few there). I think I found the feedthrough that you are referring to: https://mpfpi.com/shop/power-feedthroug ... 0234-5-cf/. I'm still very much in the demo stage, but I think that I'm going to try following your "Building an Inexpensive HV Feedthrough: The Complete Saga" post so that I won't have to upgrade my feedthrough again later once I get the necessary voltage figured out. Thanks for the tip about McMaster as well, I can't believe that I was going to spend 3x more than I need to!

Thank you very much for your help!
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Ed Meserve
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Ed Meserve »

Also check out https://www.bmisurplus.com/ ; I found some decently priced used parts there.

Regards,
Ed
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Finn Hammer »

Maxwell,

While you are at it, please get one of these viewports:

https://www.lesker.com/viewports/viewpo ... -x-ray.cfm

When you start to make neutrons, you will also get x-rays pouring out of your viewport, and a slice of lead glass will block these to acceptable levels, while you gain profficiency in operating the fusor.
Later you can use a camera, or mirrors, to avoid viewing the internals of the fusor directly, but initially, it is an asset to have a direct view of the chamber.

Cheers, Finn hammer
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

Thanks for all of the advice and suggestions! For a conflat UHV chamber, what are the best practices for connecting vacuum systems? I've seen reinforced pvc hose on demo fusors (and that's what I'm using on my demo), but I assume that that is not acceptable for lower vacuums. I haven't been able to find anything on it in the FAQ, perhaps I'm looking in the wrong place, and I've seen different, conflicting solutions in pictures of fusion systems. As this is a very different question than the initial thread, would it be best for me to make a new post in the new user chat area? Thanks!
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

Maxwell_Epstein wrote: Wed Sep 01, 2021 10:01 pm but I assume that that is not acceptable for lower vacuums
I mean higher/deeper vacuums, my bad
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Dennis P Brown
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Dennis P Brown »

For a roughing pump (a few microns to torr range), that is fine (pvc) but for high vac, no. Most use steel flex line and/or solid steel piping connectors. Type of seal, either KF (I use, simple and redoable o-ring seal) or copper gasket seal (generally needs replacement after a few uses.) Lots of pics of people in the forum showing there vacuum systems. Look at what others have done.
Around here, we often use lower vacuums when we talk about 'higher' vacuum. Terminology is secondary. As such, UHV is generally used for systems that go below 10^-6 torr and certainly are not needed for fusors. Fusor's don't need lower than 5 ^-5 torr for first clean up/pump out and generally operate in the 3 - 30 micron range.
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

So my vacuum line would look something like
roughing pump --> steel line (adapts from 1/4" connector on pump to KF?) --> TC gauge (inline) --> Valve --> diffusion pump --> steel line (KF to conflat?) --> fusor chamber?
As I do not yet have a diffusion pump, should I stick with PVC until I make the upgrade (next step after vacuum chamber)?
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Liam David »

Close.

Pump -> 1/4" (perhaps) to KF -> valve -> gauge -> diff pump -> valve -> chamber. I would recommend stainless as it's very future-proof and clean... but it depends on your budget/scrounging skills and you can get away with plastic between the roughing and diff pumps.

Ideally the only hose would be between the pump and valve or valve and gauge. The tube between the diff pump and chamber should be as wide and short as possible to keep conductance high. The valve between the diff pump and chamber must be throttleable so you don't waste deuterium. Most diff pumps also have a nonstandard flange which you'll have to adapt to conflat or KF depending on your chamber.
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

I only have a roughing pump right now so until I get a diff pump will I be able to use a thermocouple gauge or are TCs too sensitive for use without a diff pump?
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Richard Hull »

TC gauges are crude and cannot read a deep vacuum that is produced by a diff pump. That is why they are placed between the mechanical (roughing pump) and the diff or turbo pump. Another gauge is also needed it you wish to read, accurately, the vacuum in the fusion chamber. Such gauges are far more expensive gauges that can read to a far more reduced pressure in the 10e-6 torr range.

A TC gauge cannot read to one millionth of an atmosphere and a mechanical pump can't reach even that low in pressure. A billionth of an atmosphere is what most folks doing fusion try to achieve as a clean system. You need to read a lot of the vacuum FAQs and understand pressure capabilities of each pump, system and all the possible gauges used in vacuum work.

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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Dennis P Brown »

Hold off on getting a diffusion pump (DP) until you learn the issues - there are many. First and foremost - size. Too large and you will go through too much deuterium gas and/or have an issue with adapters; that is the next issue- adapting a DP flange to your system. That more often requires custom (either you or a machinist) for many cheaper pumps; higher end pumps match commercial flanges which are 1) expensive 2) often need other parts before one can couple to their chamber. Then can you handle a water cooled DP? Or can you find an air cooled one (rare.) This also means one needs to think about a manual control gate valve to control the rate that gas is removed from your fusor and help stabilize the working pressure in the fusor. Again, that will determine your deuterium gas usage (which you need to understand gas systems and how/where to get deuterium gas - an other whole topic area.) There is much more but these are main points you MUST consider before buying a DP.

AS for vacuum gauges, that is an area of its own - far simpler but getting the wrong stuff is painful, waste of resources and can lead to fusor operation failure. Then there is the issue of neutron detection - an area very few can handle as beginners but in the long run, must be mastered or it makes no sense to build a real fusor - and a demo only needs a simple mechanical pump, not a DP.
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

Thanks for the clarification regarding TC gauges. I read through the vacuum FAQ and have a better understanding of the limitations of TC gauges as well as how I should go about setting up my system. As per Dennis's suggestion (and my budget), I'm going to hold off on upgrading to a diff pump until I get my new vacuum chamber (arriving next week!) working with just my mechanical pump. It looks like a TC gauge is my next step and I found what I think is a good one on BMI surplus for ~$200. Thank you everyone for your advice, I'm diving in headfirst and couldn't be more excited!
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Dennis P Brown »

That sounds like an excellent plan. Gaining experience with vacuum systems and related vacuum gauges is a critical first step and essential before one can do fusion in any fusor. That seems somewhat high for a simple TC gauge but I don't (any more) know what deals are out there. Maybe others could offer input. You could post it and ask for feedback.
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Richard Hull »

Seems high for used TC gauge and tube. There are two parts to all TC gauges. 1.the tube, 2. the controller/readout with cable and plug. I hope you have a fully working and warranted used device that includes working tube and readout controller. If a digital readout, it is about right for that price.

Richard Hull
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Maxwell_Epstein »

The TC gauge and tubes were the "TC Vacuum Gauge for DV-6M Tube" ($125) and the "Teledyne DV-6M Vacuum Gauge Tube" ($70) on BMI surplus (link below). I decided against buying those, however, when I saw Steven Haid's "Working Fusor - Parts for Sale" post on the Parts for Sale section of the forum. I contacted him and am in the process of purchasing his thermocouple gauge setup and high voltage feedthrough. I do not currently have the equipment or experience to weld my own fusion-ready grid, so his will be very helpful - and having a TC gauge for cheap that I know has been properly calibrated and maintained will be great too. I read through his initial neutron club application post as well and learned a lot. Thanks for the quick replies about the price of the initial gauge, even with the resources here, it's been difficult for me to determine what's a fair price and where I'm being ripped off, so your help is very appreciated.

BMI Surplus Links:
Gauge: https://www.bmisurplus.com/product/tc-v ... v-6m-tube/
Tube: https://www.bmisurplus.com/product/tele ... ge-tube-2/
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Dennis P Brown
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Re: Is a Rectangular Vacuum Chamber a Good Choice for a Demo Fusor

Post by Dennis P Brown »

If fairly accurate, the 0-10 micron range display has good resolution and would appear ideal for a fusor - standard fusors tend to operate in that region; smaller fusors operate higher but that display has that range as well. You should ask about returns (and a two week window to return) if the unit does not work before buying. If not, then maybe steer clear.

On e-bay, one can often do better on price with many types of surplus units but getting a good unit can be hit or miss. With e-bay, one must be patient to find the right system. Unfortunately, finding the right deal requires some knowledge and skill since bidding can be involved.

However, if the unit Steven is selling here is working, that is a good bit lower in cost and proven in a system.
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