Fusor 1.0 - Conceptual Design 1

[lanewaddell]

Okay guys,

This is my first attempt at a conceptual design for my fusor system. I realize that the model itself has a few issues (for one the viewport is backwards. It also doesn't have bolts or connection clamps and the structural components are not shown so it is defying gravity); the point here was to model the general concept.

Color Code

Green - Needle Valve (gas regulator will be downstream of a fleixble 1/4" NPT gas hose on the lecture bottle)
Red - KF-16 all in one (screen on box) digital pressure sensors. Piezoelectric. One on gas supply side and one on vacuum side
Purple - Atmosphere vent /breaker valve - not sure if I actually need this. I have to look at the pump I'm going to buy and see if it has a vent valve on it.
Yellow - KF-25 manual butterfly valve
Not shown on the back will be the famed 30kv passthrough https://mpfpi.com/shop/power-feedthroug ... 0234-5-cf/ going through a CF 100 to CF 2.75 zero-length reducer flange.

<<<CLICK FOR IMAGE>>>
https://imgur.com/a/kVxtgZn
^^CLICK FOR IMAGE^^



What are your guy's thoughts?

Some of my questions:

• 1. CF 100 vs ISO 80/100 for the main chamber, any strong feelings there? It isn't too late to change, I just need to rework the design.
  2. Does it make sense to put the butterfly valve on the inside or the outside of the pressure sensor? Thinking about it, putting it inside of the butterfly (not what's shown) is what you HAVE to do to be able to see the differential between the chamber sensor (on left) and the roughing pump pressure (on right). So answered my own ? there.
  3. Specifically for the PRESSURE SENSORS and the NEEDLE VALVE, are there any more commonly used ones that might be cheaper easier to find that you would recommend? These are compatible but expensive (one-offs) made by specialty companies.
  4. Any other suggestions on how to make this easier, simpler, cheaper and more likely to work?

Thanks!

[lanewaddell]

[deleted]

[JoeBallantyne]

Based on the drawn layout there is no point in having 2 vacuum gauges. They will be measuring exactly the same pressure, since there are no valves in the connected system between them. So one is completely redundant. I would just remove the one close to the gas supply.

ISO and CF are both overkill in terms of the vacuum specs they meet vs what you will be pulling on that system. CF is more expensive when you add up all the costs. CF is more of a pain to work with. CF does not have reusable gaskets (assuming you use what it was designed for, which is copper).

CF is flashier, people think it is cooler. Its like driving a Mercedes/BMW/Lexus vs a Honda/Toyota.

I don't think that using KF25 vs KF16 for your pump to system plumbing is going to make much difference in your pump down rates. Especially if you keep the bellows length reasonable.

What is the point of going with a straight CF100 cross? Especially if you are going to just immediately zero length reduce it? All it does is add wasted volume to your chamber (takes longer to pump down and uses more D2) and expense (you have to buy adapters to go down to the KF you are going to use). Two legs of that cross, you are going to immediately take down to KF. So why not get it built that way to start with?

If you are getting a custom built chamber, and are worried about the diameter, I would go with an ISO100 to KF50 reducing cross. Or maybe just an ISO100 to KF25 or KF16 reducing cross. Since conical KF reducers are cheap, and the larger KF connecter gives you more options, I would probably go with the ISO100 to KF50. I like the reusable seals of ISO and KF. But if your heart is set on CF because it is the "best". Then do that. You are the one who is going to have to pay for it. In the end will using CF over ISO get you a system that makes more neutrons? Nope.

You might consider getting a bellows valve instead of a butterfly. If you go with a butterfly, I would suggest getting a KF40 or KF50 sized one as I think that gives you a bit more fine grained control over the pressure than a KF16 or KF25 butterfly.

Now if you are going to sell everything immediately after you make neutrons, it will likely be easier to sell a stock CF100 full cross for more money, than any of the alternatives proposed above.

If you go with CF, just make sure you don't damage the knife edges before you get the joints assembled. My advice would be to leave the plastic covers on each connector until you are assembling that particular one.

Joe.

[lanewaddell]

Thanks Joe this is all good stuff.

For point 1 regarding the 2 vacuum gauges, I'd love to get rid of one. I think a mistake I found is that the other gauge needs to be on the other side of the butterfly valve (facing the pump) that way the pressure differential can be measured between the mostly closed butterfly and the main chamber.

I admit CF looks much cleaner than ISO or KF...especially ISO which although it works as designed..kind of looks like a hack job with clamps holding it together. I'm trying not to let that weigh heavily on my decisions though. A digression - I also consider Toyotas to be luxury cars - I looked at one of their 'economy' models and they wanted 35k for it out the door...so I bought a chevy bolt EUV instead : p.

To the last point - and I know we've been back and forth a couple times on the chamber size. The whole idea is that I'd like to be able to do 1e6 fusions/sec. Richard Hull stated that the smallest he's seen that in is a 2.75" chamber. Separately he also said that 4" is the absolute minimum he'd do for "real fusion". So the absolute minimum is about 3" (ISO 80) based on the first statement and then ISO 100 or CF 100 (~4") based on the second statement. I don't have the ability or no-how to do complex plasma modeling so that empirical information is the best I have to go off of. That said, do you still think 3-4 inches is too large given the goal?

Thanks!

[JoeBallantyne]

Was Richard talking about 2.75 CF flanged chambers? 2.75 is a standard conflat flange size, and there have been quite a number of folks who have used 2.75 CF crosses as their chambers. Those have an actual chamber diameter of about 1.5 inches. They line up with KF40 dimensions in terms of the tubing. KF50 tubing is larger than the 2.75CF flanged tubing.

If you could post a link to the Richard Hull post you keep referring to, that would be helpful.

I have looked at some of Joe Gayo's cube fusors, and I don't think their inner diameter is 2.75 inches. I think it is less.

I am pretty sure some of the folks who built 275 CF chambers did 1e6 n/s or more in them.

I know for a fact that Joe Gayo did much higher than 1e6 n/s in his very small cubes.

You are basing a fundamental requirement of your design on like one line of text in one post.

Be very careful about that kind of thing.

The pressure differential between the pump side of the butterfly and the chamber is completely irrelevant. It doesn't matter at all. What you want to know, is the pressure of your chamber.

Joe.

[lanewaddell]

Hey Joe,

I'll dig up the posts and repost here. I don't disagree with you, but I'm kind of at loss for information there. Again, there are some things I can model well because I have the background and the information I need - plasma physics isn't one. So in principle I agree with you, but if you known any better source of information I'm all ears.

[JoeBallantyne]

Here for example is a post from Liam describing his first cube. He did well over 1e6 n/s, and its inner bore diameter is 5cm. Or just about the same as the inner diameter of KF50 tubing.

viewtopic.php?p=96481#p96481

Joe.

[lanewaddell]

This is great and really helpful! Thanks Joe!

I'm not trying to be bull-headed....believe me not trying to go broke...I just didn't have any sort of justification to go smaller.

FYI-

These are the posts I was referring to.

viewtopic.php?p=99614&hilit=fusor+size#p99614
viewtopic.php?p=87970&hilit=hard+nosed#p87970

[JoeBallantyne]

I can't find anything in the first thread of posts that says you have to have a 2.75 inch diameter chamber to do 1e6 n/s.

Neither do I find that in the second post by Richard.

And he is CLEARLY referring to 2.75 inch CF flanged chambers, which means that 2.75 is the diameter of the CF flange. NOT the diameter of the chamber itself.

KF50 tubing is about 2 inches in diameter.

CF275 tubing is about 1.5 inches in diameter.

Joe.

[JoeBallantyne]

Based on what I have seen posted on this forum over the last few years, I think it is safe to say that the vast majority of high performance fusors built in the last 5 years or so, have been machined from aluminum, and AFAIK, they ALL have been either cylindrical or cubes and have had inner bore diameters SMALLER than 4 inches. Some of the cylindrical ones, may have been longer than 4 inches in length, but their inner diameter was less than 4 inches. I think most of them had inner diameters smaller than 3 inches.

Most of the early fusors were spherical. Most of the later ones are not.

Jon Rosenstiel built both a spherical and a cube fusor. AFAIK, his cube vastly outperforms his sphere. I'm pretty sure the inner diameter of his cube is less than 3 inches.

Yes, his cube inner diameter bore is actually 1.875 inches. Basically the same as the inner diameter of KF50 parts.

See viewtopic.php?t=12954

Joe.

[lanewaddell]

Joe,

Gotta admit.... I kind of like that thing.

Maybe back to the drawing board

[Dennis P Brown]

Some time back, I showed that the diameter of the chamber was not really the relevant parameter per-se, but spacing between the cathode and ground was the critical aspect relationship.

This enabled a very large chamber to act like one that was one quarter of its original volume. That is, this reduced cathode/ground spacing which enabled a far higher operating pressure by the deuterium in this physically "same" sized chamber. So, the system went from operating at 5 microns for a stable plasma to around 20 microns operating pressure - again, the chamber was the same volume/size but its operating pressure increased dramatically.

The exact same power supply was used operating at the same current and voltage - so, no change there.

I used a screen as the anode/ground inside the chamber to create the 'reduced' sized equivalent chamber conditions.

The net result, besides the increase in pressure, was my neutron rate nearly doubled.

So the advantage with any 'smaller' chamber or its 'equivalent' is the increased operating pressure for the deuterium (maintaining a stable plasma at this higher gas pressure.) More deuterium more neutrons. Its that simple.

Building a smaller chamber - rather then modifying a larger one - has all the advantages of higher pressure/neutron count but has the added feature of being a lower cost build. Of course, people have tried taking this to extreme only to discover that there is a limit and the plasma shorting to the ground drains away all the available energy from the power supply.

I will add that while one can do fusion w/o a high vac system having that feature is advantageous. This is due to the fact one gets a far cleaner system - that is, running the chamber at a much lower pressure enables better out gassing of contaminates (of course, a plasma burn is critical as well.)

In the past, all high neutron producing fusor systems I've seen posted here have a high vac capability. Is that feature essential, useful, or just a wasted expense? Don't know for certain (if one keeps a clean system) but just thought I'd mention this aspect of past high neutron count fusors.

[lanewaddell]

This is wonderful insight thanks Dennis!

I would imagine there is an optimal size for a given set of constraints as in most things.

In my mind I see an "infinite" reactor - the effective range would be a sphere around the grid probably controlled by voltage and pressure. The chamber size needs to be at least as large as that diameter but not smaller or it shorts out as you said.

Maybe I'll look smaller.

[Joe Gayo]

Some quick comments.

- Jon R. cube fusor had nearly identical inner bore diameter to all my cubes. I know this in part because I provided the endcaps for his chamber.

- A UHV system and bake-out strongly contribute to a high-performing system. Removing impurities, especially water vapor is key. Don't waste your precious ion current on anything other than D2+.

- Cubes demand precision for high performance. Excellent cathode co-axial alignment with the chamber bore is a must. Many fine details push cubes to perform very well (Liam has posted about much of it...).

Good luck,

Joe Gayo

[lanewaddell]

Dennis,

Could you allude to the actual values you used for your effective volume comparison test?

I.e. started with a 6 inch Fusor but used a grid to reduce it to...

Might be useful. I'm really struggling to find the right size chamber which is the first thing I want to fix. I think things will start falling into place after that.

I've been looking at 4-way crosses only until this post. CF100 and ISO 80. Now I am considering maybe a CF 63 cube or 6-way cross. Unless everyone is stomping their foot to the contrary, Im thinking CF 50 is too small. So while this is great info it increases the number of options for me to struggle with.

Some "hey man, this is a good starting size" for what you want suggestions would be appreciated!

I've spent a couple weeks now just debating chamber size.

[Dennis P Brown]

The chamber is 13 inches by 13 inches from each port face. The inner body is roughly 9 inches in diameter. The steel grid was 6 inch diameter cylinder 10 inches tall.

Currently, my phone or the computer refuse to connect so I can't download any pics. Found an old pic The face plate is about 8.5 inches in diameter

[JoeBallantyne]

Lane - the right size chamber horse is dying. Please stop beating it.

People have built successful fusors in all different shapes and sizes.

You can too.

Any chamber with an inner diameter between approximately 2-4 inches should work just fine for you.

Choose already. It's YOUR decision. Please stop asking us to tell you what to do.

Joe.