Cube fusor build

For posts specifically relating to fusor design, construction, and operation.
Jon Rosenstiel
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Re: Cube fusor build

Post by Jon Rosenstiel » Tue Oct 29, 2019 10:47 pm

Richard,

The cube’s neutron numbers at 40 kV, 10 mA with the original, aluminum cathode, ID= 0.5”, OD= 1.0”, L= 0.7” was around 5.5E+05 n/s (TIER), about one-half that of my fully conditioned spherical fusor. (1.0E+06 n/s) Note that unless otherwise specified 40 kV, 10 mA was used for all testing.

Neutron numbers from my latest two test cathodes (304 SS and titanium, both with ID= 0.65”, OD= 0.75”, L= 0.75”) was around 2.8E+06 n/s, nearly a 3-times increase over my spherical fusor! (And a 5x increase over the original aluminum cathode) At 40 kV, 15 mA both cathodes produced around 3.6E+06 n/s. As to evidence of wall loading from the titanium cathode, nothing yet.

The numbers come very quickly. First run with the Ti cathode gave 1.8E+06 n/s, second run 2.4E+06 n/s. By the third run (run times: 5 to 10-minutes) the cathode reached its maximum of 2.8E+06 n/s. I remember my spherical fusor taking weeks (or more) to reach its final, best neutron output.

So, if you’re after the numbers it seems that a cross or cube is a must-have.

My simplistic take (from my simplistic mind) on how these devices get their high numbers is that they’ve taken the spherical fusor’s multiple star-mode “rays or beams” and condensed (consolidated, combined) them into two beams. Basically, the same amount of fusion stuffed into a smaller space.

Now, about TIER. TIER doesn’t really work with these devices as they do not emit neutrons isotropically. So how can we fairly compare the traditional spherical fusor’s neutron output to a cross or cube? Or can it not be done?

Jon Rosenstiel

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull » Wed Oct 30, 2019 4:00 am

I'm with Jim. Let Activation tell the tale for those of us looking for quick usable activation. It sounds like I will give the cross a shot, just to go on an adventure. I can see real advantages in the two beam system as the end plugs are easily and cheaply exchanged for experiment (beam on target). Lots of ideas and materials in mind.

Thanks for the highly detailed exposition given above. Helped out a lot.

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.

Jon Rosenstiel
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Re: Cube fusor build

Post by Jon Rosenstiel » Wed Oct 30, 2019 6:46 pm

Jim, Richard...

Right you are, it's the activation that matters. To that end, I just attempted to duplicate (as best I could) Richard Hull's HEAS silver activation experiment. A 2" diameter piece of silver 0.007" thick was placed between two 4" x 4" x 2" thick PE blocks nestled up against one of the cube's endcaps. Activation was for 5-minutes at 40 kV, 10 mA. (2.5 to 2.8E+06 n/s) At the start of the 5-minute run pressure was 22.2 mTorr, chamber temperature was 25 C. At run's end pressure was 25.7 mTorr, chamber temp was 53 C. It took about 6-seconds to transfer the silver from fusor to detector. Initial count-rate on a 2" pancake tube was over 5000 cpm. Yikes!

Jon Rosenstiel

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Jim Kovalchick
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Re: Cube fusor build

Post by Jim Kovalchick » Thu Oct 31, 2019 2:14 am

Jon,
Wow! I was hoping you would have these results. Maybe my next fusor is one like this. Activation is really on of the best amateur uses of fusion. Thanks for the careful reporting.

Jim K

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull » Thu Oct 31, 2019 3:41 am

I can't better Jim's comments, and hold with my original statement in this thread.. Jon's work is first rate,and he knows how to report to those of us who know fusion in the fusor. He knows all the key variables and what the gaining fusioneer hungers for in such reports of new ways of getting to key goals. Thanks so much Jon!

Looks like I may find myself on the cross, but hopefully, not be suffering there.

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.

Jon Rosenstiel
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Re: Cube fusor build

Post by Jon Rosenstiel » Thu Oct 31, 2019 6:47 pm

Guys, appreciate the kind words, glad I could help out in some way.

Below is a TIER comparison between my spherical fusor and the new cube.
fusor vs fusor.png
fusor vs fusor.png (47.4 KiB) Viewed 526 times
Jon Rosenstiel

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull » Thu Oct 31, 2019 7:10 pm

Nice graph! At my limit, 40kv, it appears to represent an increase of over 2.5 times in the cube/cross with cylindrical cathode. Sweet.

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.

Rex Allers
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Re: Cube fusor build

Post by Rex Allers » Thu Nov 07, 2019 3:16 am

Jon,

A few basic questions:
1) Your neutron numbers are a good bit higher with the SS and Ti cathodes vs the original aluminum, but the cathode dimensions on the newer ones also changed. Do you have any notion if the material is much of a factor vs the dimensions?

2) In one of your earlier pics you showed the two end plates after operation. The beams left a pattern on them. They seem to have a somewhat linear shape. The dimensions of the chamber and cathode are circularly symmetric. Do you have any thoughts why those patterns seem to have a linear component vs just circular.

3) Joe had originally planned to use magnets to focus the beams. Do you know if that has been done and did it have any affect?

4) Possibly dumb question: On pics of your HV feedthru there are two red rings around porcelain grooves. Do they serve some purpose like making arcing less likely or some other reason?
Rex Allers

Jon Rosenstiel
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Re: Cube fusor build

Post by Jon Rosenstiel » Sat Nov 09, 2019 11:22 pm

Rex,

Cathode construction: From what I’ve found neutron production is strongly related to cathode dimensions, and only weakly related (if at all) to cathode material.

End cap patterns: One of the reasons I posted the endcap pix was I was hoping someone would tell me about the patterns. Anyway, my take is that the dark, linear shaped patterns are where the electron “beam” strikes the endcap. (The dark material has to be aluminum from the cathode) I have no idea why the pattern is shaped as it is. I think the fainter, circular patterns may be from D2 ions. The circular patterns also seem to somewhat define the outer limits of the “neutron cone”.

Edit: Remember, I'm mainly guessing here... every time I look at those images I change my mind about what's what. With it's present SS cathode the cube has been settling down and running smoother and smoother. Perhaps in a few weeks I'll pull off the endcaps to see what they look like. Should be interesting.

Magnets: (Edited 11-10-19) Depending upon positioning, the magnets either did nothing or reduced neutron output.

HV feedthrough red-rings: Rex, those are silicone o-rings, McMaster-Carr # 1283N263. The idea came from Joe Gayo. Bore the ID of a piece of 1.25” PVC pipe out to 1.5”, slide the pipe over the o-rings and fill with mineral oil. Increases the 30 kV feedthrough’s air-side stand-off voltage two to three times. (I’ve run mine up to 70 kV and I think Joe has run his up to over 90 kV)

Jon Rosenstiel

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