Matt Gibson Cube Fusor

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Matt_Gibson
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Matt Gibson Cube Fusor

Post by Matt_Gibson »

So I’m going the cube fusor route and decided I’d start a separate thread for it. It’s an MDC 3.38” conflat cube with 2x2.75” ports and 3x3.38” ports. The largest bore diameter is 2”. While it’s a little small, I’m hoping it’s close enough to the others that it’ll perform well.

Right off the bat, I’ve hit a snag. I picked up a 3.38” to 2.75” conflat reducer. Not sure how MDC intended for this to actually work. Here is a picture of my headache, showing overlap of the 2.75” conflat over the bolt holes for the 3.38” conflat. Am I missing something here?

9D49C9F3-3E7B-49A7-A525-CB718B9695D6.jpeg
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

Note the adapter is threaded. The adapter assumes you are looking to mate the 3.38 adapter to another 3.38 flange that is not threaded, (through-hole), AND is on a tube that will allow a proper length short bolt to come through and thread in from the other side of the mating flange!

If your cube is 3.38 "face flanged", you are out of luck.

You would need a 2-inch 3.38 to 3.38 straight coupling to make this work and hook to your face-flanged cube.

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
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Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

That’s an inconvenient design…Turns out that I already have a nice little 3.38” to kf25 conical converter in one of my boxes, so crisis over!

I’ll send this back and then get on with construction. More pictures to follow.

-Matt
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

Inconvenient!! This methodology is the one and only mass manufactured solution given the fixed nature of the design of all Conflat 2.75 and 3.38 extant flanges.

3.38 is a nasty and oddball flange with adaptations and related accessories selling at a premium. However, if one is willing to custom machine and weld in work-arounds related to adaptation to 3.38, all such issues are easily taken care of. There was a very easy non-machined path in doing this and that was the simple straight through 3.38 to 3.38 short extension. The terrible part is the very high cost of the oddball ready made extension in 3.38. In this case with a face mount 3.38 the extension was not only expensive but inconvenient. Get use to inconvenience in 3.38 CF.

In short, if you go 3.38 and buy from surplus.........You should have machining capabilities on hand along with TIG welding or have deep pockets to buy often inconvenient solutions.

Note: 3.38 is great if you design with it and only it from scratch in a system design and have the need and cash to fund it.

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
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Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

Richard, all part of the learning curve…

Fortunately, this cube has a few 2.75” ports for my other stuff and I was able to get some 3.38” blanks for “cheap”.

I should be able to simply pop off my old chamber and directly mount this in place.

Any other unforeseen (to me) snafus to be aware of?

-Matt
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

Got the cube in today as well as two endcaps for it. Unfortunately (or maybe not) the port that I had planned for the viewport is 3.38” and not 2.75”. I’ll have to get creative as there isn’t much space for bolts there. I’m hoping that a seller on eBay will help me out by parting out some 3.38” viewports from a pile of 3.38” “stuff”.

How concerned should I be about those sharp edges?

Here’s some of the parts:
6046145F-FA12-48F3-A6C7-E5551669D0B0.jpeg
7C1CE522-8EEF-4176-9B70-09CA1F544979.jpeg
4BAEC40D-2BAD-47D4-98EA-F364F64A497A.jpeg
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

Chamber has been assembled. I swapped it in, briefly, to see how well it pumped down and then did a few runs.

It pulled down to 12 microns before I turned the turbo on. It then quickly went to “0.0” microns a few seconds later.

At 30kV, 5mA, 12 microns or so, there is very strong ion beam on the window. I can see blue white fluorescence in the shape of an oval that is very hot to the touch after a minute, so I removed the chamber in order to install some fused quartz glass inside.

I also hear corona discharge at 30kV. Is this from the sharp corners formed by the cube?
42CD7F5A-1CB4-4474-B851-E7880F224C3B.jpeg
8F60C3DC-128E-4DE9-9AFB-4753CFC3BE7F.jpeg
DBA8B2DF-D3F8-492A-AC2F-A514F80BC457.jpeg
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

Nice setup. Yes, the sizzle could be a brush discharge for those sharp pointed edges. Observe in total darkness. If there is a blue glow at the points it is itching to arc. Try to avoid this by using a large spark plug boot over the hot lead packed with HV silicone putty. Also, a 6X6-inch 1/4 inch thick phenolic plate with a tight fitting 2.75" hole bored to fit flat over the top of the fusor. HDPE would be ideal but it would soften and maybe even melt in contact with the hot fusor.

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.
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

Thanks Richard! Hopefully it works out…

I’m using this setup for the top connection to the feed through. Maybe it’s moving the field in such a way that those sharp edges are getting tempted? I haven’t seen the other cube fusors with this problem. I’ll try using just the brass ball instead of the toroid. If that doesn’t work, I’ll look into getting a hole saw and some phenolic.
6C084090-F5DE-4715-AAFC-D83F713A6FDD.jpeg
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

I still think a nasty old spark plug boot using a threaded cylinder extension would be ideal.
The putty I use is distributed under the GC electronics line of products. fabulous stuff!!!

https://www.google.com/search?q=GC+high ... e&ie=UTF-8

See this quick image....

Richard Hull
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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.
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

We’ve got alot of that stuff at work (electric utility) for our underground splices. I may see if they can spare some if I keep having corona issues.

-Matt
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

Sadly this may have to retire your wisely attached field control toroid on your older system. Toroid field control works best on a spherical or cylinder type of fusor where grounded surfaces immediately below the toroid and HV terminal are smoothly radiused curves. Large flat , grounded planes are OK under a toroid but they must not have any conductive protrusions, especially if they are sharp right angled ones.

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.
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

I really like my toroid, gives it that pizzazz!

Maybe I can keep my little threaded sphere? Goop and spark plug boots…😔
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

I can't believe I did not suggest a thin aluminum flat 6X6 plate, (or larger) instead of the phenolic!!! This means you might keep your toroid and the aluminum plate could do some heat sinking. Just make sure the plate is big enough so the sharp edges do not temp the toroid to arc. More heat sink would be nice. It might hide your beautiful fusor from easy viewing, of course.

It shows a bit more cogitation on a perceived issue tends to lead to possible better and better solutions.

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.
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

You got me thinking a bit more too…

What if I used a half toroid instead of the 6x6 plate? These are two piece toroids and I have another “set” sitting in a box. I could slip one half (or both pieces) in place so that the toroid covers both the cube’s edges as well as the feed through flange bolts.

-Matt
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

Sounds OK, but only doing it will tell the tale. "Let the experiment be done!" (Ben Franklin)

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.
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

Looks like the half toroid might have done the trick. I don’t hear the crackling anymore. I need to ramp up a little higher (took it up to 54kV) and then turn the lights off to be sure.

Here it is, mounted, and getting broke in (I hope). I added some quartz glass (good for 2100F) as sacrificial glass since the cathode throws a beam directly at the viewport.

So far, this thing seems to be difficult to control:

Plasma won’t strike until I approach 40 microns, with a starting voltage of 20kV. After that, moderate adjustments in voltage causes current to shoot up and my low voltage PSU (12vdc 80A) to cut off due to overload.

By the time I do the back and forth between lowering pressure and raising voltage, all while keeping current from shooting up, my car amp has overheated and I’m done until it cools off.

Not sure if this is part of the deal with such a small chamber or if this is just the new setup having to be broken in.

My much larger chamber is a breeze…
2CB097A3-B098-47C0-9B80-00340C57DE75.jpeg
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

The big chamber concept is why I and sticking with the 6" sphere. Much easier to control suitable cylinders, crosses and spheres of moderate size. they work well. Good luck in getting you rather tiny cube to work. They typically do take higher gas pressures and with that, more current.

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.
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

That’s what I was afraid of…

I think my main problem now is my PSU. Car amps don’t like being run at “high” frequency (18khz). I’m wasting an incredible amount of power via heat.

I think the cube can work, but needs a lot slower tango to get up to operation, which my car amp isn’t going to allow. I’ll have to begin working on a replacement (half bridge driven by a PWM) for the car amp.

Going to focus on getting my deuterium bottle secured properly for now. I’m wasting gas trying to fill a syringe from the regulator…Got some swagelok doodads coming soon.

After that, I’ll put my efforts towards a half bridge and then get back to this cube.
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Richard Hull
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Re: Matt Gibson Cube Fusor

Post by Richard Hull »

That green spot looks like a real x-ray source on that window.

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.
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

It’s coming off from the cathode and (now) striking the sacrificial glass. Hopefully the quartz can stand up to the heating…

Anywho, I’ve switched back to my 4-way cross until I can get a new driver configured for my transformer/CW multiplier combo.

-Matt
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

Okay so I have a question related to my power supply:

I see, from Finn Hammers nice FAQ, that full wave CW multiplier needs a two winding secondary. What happens, electrically, with just a single winding? Does the multiplier act as a half wave multiplier?

I’ve been running my multiplier with just a single winding, one end tied to one of the AC inputs and the other side of the winding, to the other AC input. Multiplier ground is the return for the fusor. Would this be damaging anything or just running at half capacity? So instead of say, 5kV (10kV pp) I’m really running 2.5kV(5kVpp)?

Anyhow, I’ve ordered two more 3D printed bobbins to get on it!

-Matt
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Re: Matt Gibson Cube Fusor

Post by Finn Hammer »

Matt,

I tried to simulate the my own multiplier in the connection you describe:
faulty multiplier.JPG
It produces this startup voltage profile:
faulty multiplier1.JPG
When simulating the multiplier in the correct configuration, I get this same startup voltage curve:
2.JPG
However, simulating the faulty circuit, up to 2.7mS took almost 5 minutes, whereas the correct circuit simulates in a couple of seconds.
This tells me something is awfully wrong, although I am unable to tell exactly what it is, apart from what we already know.
When you get the new secondaries installed, and phased correctly, you wil be fine.

Cheers, Finn Hammer
Matt_Gibson
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

Hi Finn,

That’s an interesting result! Same simulated results, but much longer to compute…

Thanks for looking into that for me.

-Matt
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Re: Matt Gibson Cube Fusor

Post by Dennis P Brown »

Curious, why are you using a syringe to feed deuterium into the system? A fine control needle valve is very easy to operate and makes gas flow and pressure control much easier.
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Re: Matt Gibson Cube Fusor

Post by Matt_Gibson »

I’m feeding the syringe into a MFC for the actual deuterium flow control. The syringe is only being used to move deuterium from the PEM (50l bottle now). Soon (waiting on some more swagelok parts), I’ll switch over to direct connect to the bottle.

-Matt
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