Cube fusor build

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

Post by Frank Sanns » Sat Aug 01, 2020 5:25 pm

Ok, so I think I have it. In an earlier post in this thread I mentioned the distance of the detector from the source. It is important because a detector is not a point. It is a volume. Most importantly it has a thickness.

For a far field measurement, a half an inch difference between the face of the detector and the center of the detector is negligible to the overall distance. The near measurement though, it becomes more and more important. At the 3.5' close measurement, having the center of measuring scintillator being a 0.5" inch farther away (not sure of Jon's exact detector dimensions) thank its face, will give a significantly lower reading with the inverse square law at play. It is my belief that that is why the curve that Joe made matches it well but I think accounting for the thickness error in the scintillator distance would tie up the accounting error.

We have to realize that even with the measurements given, they are around +/- 30% of theory. This includes operating a fusor consistently during the time of the experiment and measuring those ephemeral neutrons. All in all, I would say outstanding work to Jon!

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Re: Cube fusor build

Post by Joe Gayo » Sat Aug 01, 2020 6:02 pm

All that I've trying to show, in a general sense, is that the measurements that Jon took are best described by an anisotropy volume source, not an isotropic volume source.

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Frank Sanns
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Re: Cube fusor build

Post by Frank Sanns » Sat Aug 01, 2020 9:35 pm

Either I am not understanding the original data chart or I do not understand the interpretation. I looked through everything again and I am just not getting something here. How can it be anisotropic if measured around the fusor or is it? Is this a two dimensional x,y plot or a one dimensional linear plot? How can a count be 90 dI am not sure why I am so confused by the results. My interpretation was the graph was a perimeter measurement of the output of the fusor; a 2 D plot.

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Re: Cube fusor build

Post by Jon Rosenstiel » Sat Aug 01, 2020 10:04 pm

Frank,
I sat on that graph for quite a while because something didn't seem quite right about it, but I never could put my finger on what it was.

Here is a similar chart from the attached paper.
Screenshot 2019-12-19 15.24.59.png
DD Anisotropic neutron emission.pdf
(1.99 MiB) Downloaded 10 times
JonR

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Re: Cube fusor build

Post by Jon Rosenstiel » Sat Aug 01, 2020 10:25 pm

Detector position for the 90-degree data in an earlier post was in-line with the neutron formation area (0.75” off center) not the cube's centerline.

Below find close-up 0-degree/90-degree data taken with the detector on the cube's centerline at both 0-degrees and 90-degrees.
data_1.jpg
data_1.jpg (22.12 KiB) Viewed 194 times
Each distance data-point consisted of four 60-second runs in an alternating order. (0-deg, 90-deg, 0-deg, 90-deg) Total run time, including a warm-up, recording results, repositioning the detector, and a quick bathroom break was 58-minutes. Cube temperature was 37.6 C at the beginning and 39.3 C at the 58-munute mark. Wow, water cooling to the rescue! Input power was set to 8 mA, 44 kV. At the end of the 58-minute run the current had dropped to 7 mA and the voltage had increased to 46 kV. Chamber pressure was in the 22.5 t o23.5 mTorr range. The 1” x 22” He3 detector that I used as a control was positioned 36” from the fusor. It’s highest count-rate (406 cps) occurred during the 3.75” run. It’s lowest count-rate (392 cps) occurred at the very end of the 6.25" run. Wow again, seems impossible, doesn't it? I didn’t measure the cube’s TIER, but based on previous runs it was probably around 2.0E+06 n/s.

Plotting the 0 / 90 data in Excel: Best fit (r^2 value of 0.97) was obtained with a power trendline. At this point I’m not really sure if what I’m doing is kosher, and I know it’s dangerous to extend a trendline too far out (thinking about a Corona-virus chart from our government that showed the virus gone by the end of May) but anyway, here it is.

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0-90 chart.jpg
0 / 90 chart

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull » Sun Aug 02, 2020 1:36 am

I believe and assume from Jon's report that the movable device that made the measurements was the 2" diameter BC-720 work-alike on a PMT which detects only fast neutrons, not needing a moderator with only about .1% efficiency for the scintillator. You need a hot source to make it sing. (low CPM readings) I also assume it read face on, thus a very narrow frontal volume of detection exposure. The scintillator is a 2"- dia. X ~1" thick detector. I do not think or assume his ratios were not done using the larger volume of the moderated 3He system. At least this is what I read back on page #4. Correct me if I am wrong Jon.

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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.

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Re: Cube fusor build

Post by Jon Rosenstiel » Sun Aug 02, 2020 2:04 am

Except for the detector’s thickness (it’s 5/8” thick) you’ve got it right, Richard.

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Re: Cube fusor build

Post by Frank Sanns » Sun Aug 02, 2020 11:49 pm

Jim,

I have have waited to evaluate Jon's data before I answered your question. It would seem that loading to displace gas from the shell and to provide more fuel when hit by a collision or just something coming out of the interstices of the metal then I can by into that. It seems a much harder stretch to believe there is much beam on target going on there compared to what is happening at the cathode. After all, the highest energy deuterons (with no circulation present) is at front grid surface. Any collisions there would have the best chance of having enough energy for fusion. It is also the smallest surface area and the higher current density in the fusor so it should load the fastest. And as you said, can unload the fastest at high temperatures.

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