Cube fusor build

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

Post by Richard Hull » Sun Feb 07, 2021 9:14 pm

I agree 100% with Jim. Deposition related to high field points on the cylinder. You can the it on the stalk in the photo. There is a rather even deposit due to uniform field about the smooth high field stalk

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 » Sun Feb 07, 2021 11:55 pm

I think Jim may have hit upon what's going on here.

Below images are of a brand new, freshly machined aluminum (6061-T6) cathode. I believe the greenish plasma is related to the “burning off” of aluminum oxide and/or other contaminates.

As a side note, neutron production rate of this cathode was about one-fourth that of its similarly dimensioned stainless-steel counterpart.

Jon Rosenstiel
Attachments
Al-1.jpg
9-minutes into initial conditioning run. (20 kV, 15 mA, 14.3 mTorr)
Al-2.jpg
16-minutes into initial conditioning run. (20 kV, 15 mA, 24.9 mTorr)
Al-3.jpg
2 ~ 3-hours of runtime and several runs later. (20 kV, 15 mA)

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Jim Kovalchick
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Re: Cube fusor build

Post by Jim Kovalchick » Mon Feb 08, 2021 2:14 pm

I actually posted an inquiry about the color bands before and posted some of my own pictures. viewtopic.php?f=18&t=13077&p=87033#p87033

I didn't understand them either. I have since come to the conclusion that the only things that could be making uniform and distinct color transitions are fields.

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull » Mon Feb 08, 2021 5:37 pm

I have yapped about fields for years here and a full understanding of them in the assembly of our super high voltage systems is key to avoid arcing internal or external to the system and naturally to deposition. Most of my knowledge and respect for high field conditions grew from the 12 years spent in Tesla coiling. The beautiful diamond lozenge images in the inner spherical shell of fusor III and IV due to the geodesic grid photographed 15 years ago, spoke to the field causal distribution of material via the multi-beaming ports. This is a form of incidental electrostatic focusing, deposition and heating.

For most every person in electronics 100 DC volts is considered high voltage for we fusion folks, 10,000 volts DC is considered far too low a voltage of any genuine value. Tesla coilers work in the million plus volt range albeit at RF frequencies. Field control is far more important in preventing arcing and huge electrical losses due to corona, (which can foster arcing). However it can also affect and control deposition in high voltage components in a vacuum system. I have grown so use to such depositions over these many years, I just do not give such things a second thought beyond being an indicator of high field regions, which are to be avoided or looked at as a possible danger point in the system. It also indicates a point of lost energy in the system or, conversely, a point of successful deposition where desired.

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: Characterizing the cube fusor’s neutron flux

Post by Jon Rosenstiel » Mon May 03, 2021 10:31 pm

Previous work with a 2” BC-720 replica fast neutron detector showed that the cube fusor’s neutron emissions were anisotropic in nature. viewtopic.php?f=6&t=12954&hilit=anisotropic&start=30

In order to “see” this in more detail I used a Hornyak button 8mm in diameter by 5/8” thick coupled to a Hamamatsu R6095 28mm PMT. This detector was then swept across the cube’s left end from edge to edge (100mm, 4”) using a linear stage. Data was recorded every 5mm. (One turn of the stage’s crank handle)

As I had no idea of the sensitivity of such a small Hornyak button I decided to cast three buttons of 8, 10, and 12mm in diameter. The buttons consisted of a mixture of ZnS(Ag) and casting resin. Mixing ratio was 5.7% by weight. The buttons, once hardened, were centered in HDPE molds 28mm in diameter and back-filled with clear resin. After hardening, the ends of buttons were machined flat, wet sanded, and then polished on a buffing wheel.

The 28mm Hamamatsu PMT and its housing are SAIC surplus. I have a few of these on hand courtesy of George Schmermund, but they are also often found on eBay. The machined aluminum endcap was my doing.

The SAIC units have a plus/minus 5V powered preamp attached to the PMT’s base, but the output is a 1-micorsecond wide pulse that doesn’t play well with spectroscopy electronics. I ended up taking the output off of the anode’s coupling capacitor and feeding it into an Ortec 113 preamp.

NIM electronics were comprised of a Canberra 3102D hv supply, an Ortec 572 spec amp, Ortec 550 SCA, Ortec 773 timer/counter and an Ortec 778 dual counter.

The “control” fast detector used to monitor NPR was a 2” diameter by 0.45” thick Hornyak button coupled to an EMI 9266 PMT. Electronics consisted of a Ortec 113 preamp, Ortec 571 spec amp, Ortec 550 SCA, and a Canberra 3102D hv supply. SCA output was fed into the 778 dual counter.

As each data run took around 30-minutes to complete, stable operation of the fusor was critical. Some of the steps taken to ensure stability. 1) Using another fast detector to monitor NPR. 2) Running at low power, 50 kV, 6 mA, 300 W, TIER of about 2.4E+06 n/s. 3) Directing the outlet of a portable A/C unit into the cube’s water-cooling radiator. 4) Running early afternoon when my lab’s temperature was most stable. 5) Long warm-up/conditioning period.

Jon Rosenstiel
Attachments
Chart_01.png
Data
Pic_02.jpg
8, 10, 12mm Hornyak buttons with PMT
Pic_03.jpg
The setup

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull » Tue May 04, 2021 3:40 am

Great data and presentation! Seems reasonable as the focus is very beam on target. I was rather stunned there was so much off axis neutron detection. Scattering might explain that, but so might some isotropic production in velocity space or maybe simple Maxwellian neutral-fast fusion. As always, follow the beaming where it exists. I am more tempted to go with scattering.

Great work with the homemade hornyak neutron detectors!

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.

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Jim Kovalchick
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Re: Cube fusor build

Post by Jim Kovalchick » Tue May 04, 2021 8:43 am

As always Jon, you work is mastery.
.
I wonder if your work means that everyone who thinks they know their tier numbers needs to rethink it. I have speculated on this in the past when people have parked bubble detectors right next to their fusors and then over simplified an impossibly complex geometry by using point source calculation.

Jim K

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Jim Kovalchick
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Re: Cube fusor build

Post by Jim Kovalchick » Tue May 04, 2021 8:43 am

As always Jon, your work is mastery.
.
I wonder if your work means that everyone who thinks they know their tier numbers needs to rethink it. I have speculated on this in the past when people have parked bubble detectors right next to their fusors and then over simplified an impossibly complex geometry by using point source calculation.

Jim K

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Frank Sanns
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Re: Cube fusor build

Post by Frank Sanns » Tue May 04, 2021 2:48 pm

I was out your way for a few days last week Jon but could not get the time to get over to see you. Seems traffic has picked back up since the pandemic is winding down and we are becoming immobile again due to antiquated single person transportation systems.

My fusor does not get run for the multiple hours at a time on multiple consecutive days that many of you do. When I am done with a run, I bring the pressure part way back up with a bit of deuterium before letting it sit until I get back to it. It seems to accelerate the restart up to good neutron numbers again.

A 50 KeV deuteron alone is not going to change the direction of a 2.4 MeV neutron just based on collisional vectors. O-P is something else of course.

At first I was wondering why there was a discontinuity of the function (top three points on your graph) as you neared the top of the peak but I guess that is due to the diameter of the detector and the neutron production areas not being point sources. Still, it tells something of the production. Can you do a cure fit and find the equation for the curve for all but the top three points? Does it follow the inverse square law? If you post the data we can do it. Guess I could pick it off the graph but you may have already done it.

Great work! I really wish I would have had more time last week. Alway enjoy the visits.

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Mark Rowley
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Re: Cube fusor build

Post by Mark Rowley » Tue May 04, 2021 7:10 pm

DIY efforts like this are the best. Another outstanding presentation Jon.

Aside from the stellar work of casting your own buttons, the efforts you put into establishing a very stable and consistent neutron output are notable. Regarding chamber cooling, I’ve noticed here that 18 Celsius seems to be the magic number for stability. Anything below seems to be inconsequential and above the numbers begin to vary a bit more. What is the optimal temp for your chamber?

Mark Rowley

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