Cube fusor build

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

Post by Jon Rosenstiel »

A lab get-together with Joe Gayo and 13” length of 4” x 4” 6061-t6 aluminum courtesy Bruce Meagher was the impetus I needed to embark on this cube fusor build. Start to finish took a little over one month. The following images document the build.

4 x 4 x 13 6061.jpg
4-inch square x 13” chunk of 6061-t6 aluminum courtesy fellow forum member Bruce Meagher. Thanks-much, Bruce!

Boring.jpg
Boring the 1.875” diameter through hole. Lathe is a 14.5” swing Logan.

Tapping.jpg
Tapping 10-32 thread for KF-40 viewport bulkhead clamp.

Cathode 1.jpg
I could not figure out how to make a one-piece cathode using the equipment I have on hand so I built it out of two pieces which were shrink-fit together. (Shrunk-fit??) The “torus” shape was machined using a ½” corner radius end mill mounted in my lathe’s boring bar holder.

Cathode 2.jpg
Shows the cathode in position. Shortly after this photo was taken the cube went back to the mill to have its scratched surfaces cleaned up with the fly cutter.

Cathode 3.jpg
Cathode and endcap. I initially thought that the endcaps were parabolic in shape so I didn’t even consider trying to machine them myself. I ended up getting a set of endcaps from Joe, in trade for a pulse height analyzer. Turns out the dish in the endcaps is not parabolic but spherical with a radius (as near as I can measure) of around 1.75”. Still kind of difficult to machine on manual equipment, but not impossible.

Assembled.JPG
Surfaces have been cleaned up, the cube has been washed in Citranox and then assembled. To the right of the cube are some test cathodes… it was a bit tricky getting the shrink fit just right. After assembly I sat at the workbench with the cube in front of me and wondered what the heck had just happened. Kind of threw me into a funk that the building part took a good month while the assembly part was over in a few minutes. That was it?

Under vacuum 1.JPG
I tried to configure the various connections (vacuum pump port, pressure measurement, gas feed and power) to match that of my normal fusor so swapping fusors would not be too difficult.

Under vacuum 2.JPG
Another view. Under the fusor bench is a smallish squirrel cage blower (about 1/20 HP) with its outlet directed up through an opening in the benchtop. The 10” x 10” x 3/8” aluminum plate the cube is bolted is meant to act as a radiator. It appears that the majority of the heat produced by the cube is produced where the plasma strikes the endcaps, so the best bet may be to directly cool the endcaps, either cooling fins with forced air or better yet, liquid cooling.

Plasma, 40 kV, 10 mA.jpg
Plasma image at 40 kV, 10 mA.


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Richard Hull
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Re: Cube fusor build

Post by Richard Hull »

Fabulous effort Jon! We will be interested to hear of the numbers that you get from this plus ultra little assembly. I just gotta' do a cross. I have all the stuff on hand. This maybe the last HEAS event where fusor IV will be the show. Naturally, I'll hold on to it just in case I am not pleased with the future cross effort. It has been a real trooper since 2004.

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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Re: Cube fusor build

Post by Rex Allers »

Jon,

Congratulations (again).

I recall that you originally posted this before today (Sep 12). I assume that post was one of the recent ones that was lost when the site moved.

Just for history, do you recall the approximate date you made the original posting?
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Jon Rosenstiel
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Re: Cube fusor build

Post by Jon Rosenstiel »

Hi Rex,

My original posting went up around the 15th or 16th of August.

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Re: Cube fusor build

Post by Jon Rosenstiel »

Cube fusor update… NEUTRONS!

First light occurred on the afternoon of August 15th. It was a short 3 to 4-minute run to make sure everything worked as it should. Thankfully there was no magic smoke but there were lots of x-rays and a few chirps from the Ludlum 12-4 rem-ball neutron detector. Awesome!

I managed to get in four runs the following day, total run time was 23-minutes.

Run #1: 4-minutes at 40 kV, 10 mA. (For me 40 kV @ 10 mA is somewhat of a standard as my regular fusor, when fully conditioned, will put out right at 1.0E+06 n/s TIER at a pressure of around 11 mTorr) At this same power level TIER for the cube was 2.8E+05 n/s at a pressure of 16.3 mTorr. X-rays a few inches from the cube’s endcap were well over 5 R/hr. (Measured on an Eberline RO-3C “cutie-pie” ion chamber)

Run #2: 10-minutes at 40 kV, 10 mA. Max TIER for this run was 5.3E+05 n/s at 20.6 mTorr.

Run #3: 3-minutes at 40 kV, 10 mA, then 3-minutes at 50 kV, 10 mA. Max TIER at 50 kV was 9.0E+05 n/s.

Run #4: 3-minutes at 40 kV, 10 mA, max TIER was 6.0E+05 n/s at 20.6 mTorr.

Fast-forward a month and a half and I’m still getting 5 to 6E+05 n/s at 20.6 mTorr out of the cube. I was kind of bummed about the neutron count not improving further, but a look back through my notes from the above runs revealed some real positives that I had previously overlooked.

1. 2.8E+05 n/s on the first run is very impressive. In an unconditioned state my stainless-steel shelled fusor will only do half of that.
2. 5.3E+05 n/s on the second run of the day was really, really impressive considering total run time up to this point was under 10-minutes.

Due to D2 wall loading it takes some time for the pressure in a normal stainless-steel shelled fusor to return to baseline after a run whereas the cube’s pressure drops like a brick. So next step for the cube is a titanium cathode. Let’s see if we can encourage a little wall loading.

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull »

As usual a great report from a seasoned, trusted veteran among us! Your numbers kind'a bummed me a bit, too, as I trust your numbers sometimes more than anyone else. Your work is always first rate. You might look into the hydrogen absoption rate in aluminum compared to the 304 SS alloy metals. It may not load well or unload easily.

I am a little shaky now on s--- canning fusor IV, but will still press forward with an SS cross fusor as per my recent posting in construction forum.

I will watch intently, you work..

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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Jim Kovalchick
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Re: Cube fusor build

Post by Jim Kovalchick »

I have held skepticism for some of the neutron numbers people have reported using bubble detectors for the small cross fusors because the geometry doesn't make sense to me. So, when Jon reports these numbers using his instruments my skepticism of other people's numbers is further supported.

I think that assuming point source geometry when a bubble detector is parked that close to the shell is flawed. Further we are not even fully certain where all the fusion events are happening. I think smaller fusors compound the error.

Also, are big numbers really that important? I think it depends what one wants to do with the fusor. For example, if activation is the goal, perhaps a smaller fusor allows placing the target with moderator and/or reflector closer such that a greater fraction of the total neutrons are intercepted. In a bigger fusor, the total neutrons are bigger but the target is necessarily further from the poisser, and at that point the flux is lower. Geometry is important.

I haven't seen much activation data from the small crosses reported here. Maybe that's something left to test.

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Re: Cube fusor build

Post by Jon Rosenstiel »

Jim,

I think the neutron numbers Joe Gayo has put forth are the real deal. viewtopic.php?f=6&t=12826

Joe and I have gotten together here in my lab on a couple of occasions and I feel he is on the up and up. (And as I recall, Joe does have two other neutron detectors that backup the BTI results)

The cube I built was based off of what was presented in Joe’s video and what little he told me during our visits. (Basically, what I built is what Joe started with, not what he’s currently running) Understandably, I think, Joe is playing it close to the vest and doesn’t want to spill all of the beans. (If it were me I would be doing the same)

In an attempt to determine exactly where the neutrons originated in the cube (center or endcaps) I tried applying the inverse square law to neutrons using a BC-720 replica fast neutron detector, but my results were all over the place. I’m not sure, but I think the poor results may have been due to inelastic scattering reactions, prompt neutron-gamma reactions, absorption in the atmosphere, etc., etc. In any case, I need to look into this a little further.

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Jim Kovalchick
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Re: Cube fusor build

Post by Jim Kovalchick »

Thanks for the response Jon.

I think your numbers being all over the place as you say illustrate my concern about inverse square simplicity. I think the relative size of the source, its non-point source nature, and the detector geometries confound it. I suspect MCNP would probably help but only after the true nature of the source is understood.

Regards,

Jim
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Re: Cube fusor build

Post by Jon Rosenstiel »

Jim,
I think I may have figured this out, please let me know what you think.

Off-axis tests using my BC-720 replica fast neutron detector showed that the faint circles seen on the cube’s endplates (image below) roughly define the outer limits of the cube’s neutron emission cone. Plugging the circle’s diameter (1.1”) and the distance to the cathode’s center (1.9”) into an online isosceles triangle calculator gave an apex angle for the emission cone of about 34 degrees.
Endcap, 800 x 480.png
So anyway, while looking at one of the endcaps the thought occurred to me that if one halved the emission cone’s 1.1” diameter (through clever cathode design and/or magnets) the neutron output would, if everything else stayed the same, quadruple. (Same number of neutrons packed into a much smaller area)

And one more thing… Using TIER (Total Isotropic Emission Rate) to quantify the cube’s neutron emission rate is not correct because the cube is not emitting neutrons in all directions. Question is, how should we go about comparing the traditional fusor to something that’s anisotropic?

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull »

If I remember correctly, from my old readings, fusion of D-D via tunneling is perfectly isotropic and cares not a whit about the field conditions or original collisional directions. Anisotropy is more a function of reflection and scattering after the totally isotropic fusion event, itself. This makes sense as the original directions of the deuterons or fast neutrals are under 50kev. The reaction zone at the instant of fusion produces a net energy on the order of several meV. This swamps out any lower energy directional momentum plus any electric field conditions as far as the neutrons are concerned. The neutrons go wherever they want to and that nets out to isotropic emission.

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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Re: Cube fusor build

Post by Jon Rosenstiel »

Richard,

The reaction may be isotropic in nature, but the neutrons coming out of the cube are definitely not. Both Joe and I have confirmed that the cube's neutron "output" or "flux" is about four times stronger in line with the plasma beam than at right angles to the beam.

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Re: Cube fusor build

Post by Richard Hull »

If this is true then it points to the ion streamlines impacting possible buried deuterium on the end plugs. (A form of beam on target where the source of the reaction is not within the grid and perhaps not even in the ion streamlines.) Two fusion emission points. Worth looking 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
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Re: Cube fusor build

Post by Jon Rosenstiel »

Titanium cathode testing. One of titanium's downsides is outgassing when it becomes red-hot.
Ti cathode_640_jpg.jpg
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Re: Cube fusor build

Post by Richard Hull »

Get yer red hots, right here!! The old call from vendors at ball games is apropos here. That is one hot Ti electrode.

Jon, guide me here with some of your long working wisdom and your current efforts and opinions with the cross/cube. I look at them as being one and the same.

How are the neutron numbers coming, Jon? Are they tough to get compared to your spherical system? I am about to take down fusor IV to monkey with the small CF cross idea. In your honest opinion, is it worth it for those who need neutrons? You are a solid guy with the good gear like only a few of us possess. Talk candidly here as I do not seek a new path for the sake of newness, nor am I just looking for a first pass win like so many newbies. I like neutrons and not fusion. Unfortunately, fusion is a route to obtaining those neuts. Do you think it is a good idea to cast off the old working system in favor of the cross if neutrons are the criteria?

While the cross can be an easy in for doing fusion and proving it at the newbie level, is it a real good neutron producer.

If a mega mark is tough for you to reach in the small system, I will still dismantle fusor IV and totally revamp the system to a much needed upgrade from the old 2004 original build. For the foreseeable future, I am voltage limited to 45kv max with 40kv more likely to be my limit. As you know, I struggle to get, but regularly do get, 10e6 neutrons or a bit more with luck and several days of "run in".

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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Re: Cube fusor build

Post by Jon Rosenstiel »

Richard,

I'll have some answers for you in a few days, I'm still trying to digest results I'm seeing from the titanium cathode.

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Re: Cube fusor build

Post by Richard Hull »

One has to be also concerned about the anisotropy that you noticed in the previous post related to the cylinder electrode which seems more beam on target related. The BC-720 neutron detector is about the smallest rather directional neutron detector one might employ to look for signs of anisotropy. Unfortunately you have to have a rather rich source of neutrons to rely on its typical 0.5% efficiency.

My very first fusion was detected back in 1999 using a BC-720 I paid a small fortune for from Bicron. I might have to pull it out of storage in future for use with big neutron numbers.

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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Re: Cube fusor build

Post by Jon Rosenstiel »

Richard,

Joe Gayo found an interesting paper on isotropy / anisotropy.

Link to Joe's post...
viewtopic.php?f=6&t=12149&start=30

Link to the paper... (See pages 18 & 19)
https://ir.library.dc-uoit.ca/bitstream ... Leslie.pdf

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Re: Cube fusor build

Post by Richard Hull »

I can now see how your system as made here can be more neutron directed that our classic fusor being a loose form of beam on target due to the low energies we tend to use. This being the case, why aren't the more focused directional neutron number you get far above those of the spherical more isotropic system?

Oops I re-read some of the old posts regarding the poor numbers and understand you will be running and reporting on loading with the new titanium cylinder, which you have not reported on yet. Sorry, you advised me to wait a while as you will be doing this next. Memory, ain't what it used to be.

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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Jim Kovalchick
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Re: Cube fusor build

Post by Jim Kovalchick »

Jon,
You are making good efforts trying to understand the neutron emission spatial characterization.
I'm far from expert, but I sense that emissions in your latest device are too complex to understand with conventional detectors. CR-39 plastic placed at various orientations might shed some light.

I think Monte Carlo in the right hands might be the answer.

Getting down to it, I'm not sure I would care if I were you. For me, it would be more about does this configuration let me get an activation sample in a higher flux because that is what I want to do with my neutrons. Even if fusion rates are smaller, the geometry may let you get samples closer to the point of neutron birth. Maybe you can compare activation to your original fusor. Another side benefit could be that new one uses less D. Who knows, but those questions' answers maybe more important than total numbers.
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Re: Cube fusor build

Post by Jon Rosenstiel »

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?

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Re: Cube fusor build

Post by Richard Hull »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Cube fusor build

Post by Jon Rosenstiel »

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!

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Re: Cube fusor build

Post by Jim Kovalchick »

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.

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Re: Cube fusor build

Post by Richard Hull »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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