Fusor Forums

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)?

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.

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?

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.

Richard Hull

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.

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!

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.

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

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/

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.