Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

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Rayan Alyousef
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Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Rayan Alyousef »

Currently planning out the parts to buy for my fusor build. I'm going to use a 3-way cross pipe tee vacuum chamber, with the vacuum pump + gauge connected to a KF-16 cross flange on one side. On the 2nd port I'll connect the HV feedthrough, and the third will serve as a viewing bay. I'm unsure right now on where to connect the gas inlet. Would appreciate any suggestions or guidance!
JoeBallantyne
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by JoeBallantyne »

If you want to guarantee that the gas flows across the cathode before getting pumped out of the chamber, put the gas inlet on one side of the cathode, and the vacuum pump connector on the opposite side.

Simplest way to do that is to either just use a 4 way cross instead of a 3 way tee, or use 2 3 way tees connected together. (I did the latter, although I think it probably would have been a simpler solution to just use a 4 way cross.)

Put vacuum on one side, put gas inlet exactly opposite. Put HV input on one of the other ports, and the viewport exactly opposite that. This does mean the viewport will be looking at the cathode from the bottom instead of the side, but that doesn't really matter.

In the end, at the pressures where fusors typically work, and depending on how you actually run your fusor, ensuring that gas flows across the cathode may not really be required for successful fusor operation, but from the point of view of not wanting your precious deuterium from getting pumped directly from inlet to outlet without ever even getting in the vicinity of the cathode, its nice to NOT have the inlet and outlet right next to each other with the cathode further away.

Joe.
JoeBallantyne
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by JoeBallantyne »

It is probably less expensive to get a 4-way KF50 cross, than it is to buy 2 3-way KF50 tees.

KF50 vacuum hardware works great for a fusor, and it is cheap and easy to use.

Much simpler than dealing with conflat, and you don't have to have a big chamber to do fusion.

If you want to minimize your costs, use KF fittings to build your fusor. In my experience KF50 works very well.

KF40 is getting a bit small in inside diameter IMO, you will have to build quite a small cathode if you use it instead of KF50.

Joe.
Rayan Alyousef
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Rayan Alyousef »

Hi Joe, with the 4-way setup you mentioned, where would I connect the vacuum gauge? Also, I'm looking at the KF50 online, and I notice they don't have screw holes to bolt onto, will I need to DIY make drill holes?
Rayan Alyousef
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Rayan Alyousef »

Btw, why are CF difficult to deal with?
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Liam David
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Liam David »

Rayan, I suggest you do a little more reading about the standard vacuum flanges and their connection methods. Searching "kf flange" or "conflat flange" pulls up a myriad of images demonstrating how they work. KF flanges use clamps and o-rings with centering rings. They're a lot easier to assemble and take apart than conflat flanges and are probably a better option for you.

A tee chamber is rather limiting in ports unless you were to use multi-way flange adapters. I'd suggest at least a 4-way, if not a 6-way.

Use CAD or make a drawing of your ideas--we can give you much better feedback that way.

Conflats are assembled with bolts, which are inherently more of a pain than a simple clamp. Unless you use Viton o-rings, the conflat copper gaskets are technically one-time use (multiple uses are ok if you know what you're doing). If you keep disassembling and reassembling your chamber, the copper gasket cost can start to add up. I have a stack of ~50 used gaskets from my years of fiddling with these systems, and that's only from a few major reassemblies. KF flanges have none of these concerns, although they do have their own drawbacks.
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Dennis P Brown
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Dennis P Brown »

It isn't important where you connect the gas inlet or generally most of the various devices on the fusor body; at the pressures a fusor works the gas will spread out uniformly regardless of the exhaust port. Ditto the vacuum gauge. This assumes these are connected to the main chamber and are not off on an extended adapter.

That said, locations for various equipment is best determined by equipment size/weight & build location. The main fore pump and the required high vacuum system pump (turbo or diffusion) location relative to the chamber require enough room so long vacuum lines are not required. These often are the big and heavy pieces. Also, the high voltage adapter - these require a high voltage cable and location for that - again - is best determined relative to the power supply location. Keep an eye on safety. Power supplies tend to be heavy and/or large.

A view port is an essential when first trying to learn how to control the plasma ignition on start up. If you are using a power supply over 15 kV, start considering X-ray issues.

I like KF connectors because they are less expensive, work great for a fusor, easy to remove when changing the fusor configuration or making repairs, easy to leak check, are generally available on ebay cheap and easy to repair. Not good for really high vacuum or ultra clean systems. Generally, fusors are neither of these.
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Richard Hull
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Richard Hull »

I'm glad you pointed this out Dennis. Before I studied vacuum to a greater degree I was of the opinion that Joe espoused. At fusor pressures we are in molecular flow. In this regime molecules are just free to bounce all over and never see the turbo as a source of negative pressure as would be the case in viscous flow regime at higher pressures. All Deuterium gas molecules just as soon hit the walls or the viewport as go down the throat of the turbo.

Of course, you can locate the gas inlet any where you want and opposite the turbo side of the chamber is fine, as suggested, if it makes one feel good.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Liam David
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Liam David »

Just because fusors operate in the molecular or transitional flow regimes does NOT mean that the location of the gas inlet is unimportant. For example, if your gas comes in and has a 50% chance of "turning left" and entering your chamber and a 50% chance of "turning right" and heading towards your pump, you've effectively just wasted half your gas. There may not be viscous flow and hence no pressure force on any given molecule, but kinetic physics and probability certainly still apply. This is, of course, very geometry dependent. Put the gas inlet as far away from the pump inlet as is reasonable.
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Richard Hull
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Richard Hull »

In an active spherical fusor you have a velocity space of a mix of neutral and charged particles. All gas entering the system is neutral until ionized by the hail of electrons mostly heading for the wall of the vessel. (Where the gas inlet is located) Once ionized they are urged electrostatically to the inner grid. The probability of any given percentage turning left or right or going in any direction cannot be 50% that is a dream. For spherical systems I prefer to locate at a right angle on the sphere to the pump port. (Quadrature) In this manner there is very tiny chance of any significant number of neutral molecules just entering the maelstrom ending up heading un-impeded immediately for the pump port. As we are differentially pumping, there will forever be lost gas and most of this loss is due to fast neutrals as anything positively charged with attempt a run at the grid.

Gas just introduced rarely stands much chance of remaining a slow moving neutral making a beeline for the right angled vacuum port as, in a sphere, a perfect right angle turn would hit the wall first.

In a working fusor, in velocity space, there is a mime of, but not a true, directed, viscous flow. The hole to the pump is still just a port for things to wander into or get blasted into.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
JoeBallantyne
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by JoeBallantyne »

Rayan, you asked me where to connect the vacuum gauge.

I built my fusor using KF parts. If you want to read about the whole saga and what I learned you can find it here:

viewtopic.php?p=98090

I'm planning on building another fusor with a 6 way KF50 cross, but those are a LOT more expensive than a 4 way.

Unless you want to lay out $300+ for a new 6-way KF50 cross, just use a 4 way (more like $50 or so), and connect appropriate adapters and other smaller KF hardware to get additional connection points.

Joe.
Matt_Gibson
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Matt_Gibson »

This is something that I’ve been thinking about for some time now. Here’s a shot of where my gas comes in. It’s definitely not in what one would think is “ideal”. What do you guys think?
IMG_2306.jpeg
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Rich Gorski
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Re: Where to Connect Gas Inlet in a 3-Way Cross Pipe Tee Vacuum Chamber

Post by Rich Gorski »

Rayan,

In my opinion a 3 way Tee does not have enough ports. As indicated above a 4 way KF50 (or larger) seems like a minimum place to start. Listing the minimum needed ports below we have:
1 Vacuum pump
2 HV feed through
3 View port
4 Vacuum gauge/gas feed

So, if you combine gas feed and vac gauge a 4 way Tee is the minimum needed. I would not put the gas feed on the same port as the vacuum pump as that seems like a way to waste precious deuterium gas (at fusor pressure of 10 mTorr were in the transition region between viscous flow and molecular flow). In my system I have a gate valve installed between the vacuum pump and chamber as a way to control the pumping speed and not waste deuterium gas. The gas inlet is on another port. The gate is fully open for pump down into the 10-5 10-6 Torr range and then closed so that it's only open a crack to maintain normal fusor pressure between 1-20mTorr by adjusting the gas feed through a leak valve.

Here's a simple sketch of how I would start off.
vac-sketch.jpg
Good luck with your build.
Rich G.
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