Fusor progress, Finn Hammer

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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer »

First Neutrons!!

Noooo, not produced, but measured!, I think.

It all started like this:
IMG_20171117_145419.jpg
And if you can guess what it is, then you are good. It is the first pour of paraffin into a HDPE container made from surplus pipe I found in the Water departments Dumpster. Polyethylene is getting awfully expensive these days, and this is what they got. Food grade HDPE, nothing less, doesn't get any better than that.

Outside 8 inches. hole 2, so all in all 3 good inches of moderator. Made it 450mm long for a total of 14kg.

Looks like this with both endcaps welded on, hope it doesn't explode one day:
IMG_20171120_203933.jpg
I couldn't help myself, had to jerry rig a detector harness, and test if it is able to detect some maverick cosmic neutrons, now moderated to thermal velocities, and this is the setup. Not pretty, I admit, and a lot of humm radiated into that setup, definately room for improvements on that account, but anyway, this is what it looks like in the business end:
IMG_20171120_203707.jpg
It cannot get much worse than this, really.

But hey! It seems to work.
I buried my best СИ-19Н tube deep in the gut of that mother of all moderators, and sure enough, before a half a minute, this is what I saw:
DS1104Z_20171120-203822.png
Arrh, sorry, nudge nudge, gotta zoom in a bit:
DS1104Z_20171120-203911.png
That's more like it, looks just like a neutron hit to me, as from what I read around the forum these days.

One more:
DS1104Z_20171120-090114.png
And another one:
DS1104Z_20171120-085601.png
100Mohm series resistor and all in all the same setup that Bob Higgins has proposed. On a 5 minutes run I counted 15 hits, but half of those were perhaps weak enough to get buried in gamma noise. I have 1900V on the hot side of those 100M.
Shouldn't be to hard to detect with a comparator, and an arduino could count these hits via an interrupt pin, display totals and even calculate averages on the fly too.

So this is it for today, I am happy, nothing beats progressing, and I have been looking forward to being able to detect neutrons for a while now.


I wish I had a strong source to help discriminate Gamma ray induced noise, but the best I can manage at the time is a piece of fiestaware, and it does not induce any change to the output of the tube, so hopefully that dial off a MIG2 oxygen indicator gauge which I've got coming will prove hot enough.

The smooth curves you see up ahead are the ones grabbed at 500ms per div. In the case I grab them real time, with 1ms per div, it looks like this:
DS1104Z_20171120-212337.png
But who cares? It is that sweet clean front edge we are going to trigger on anyway.

(But honestly, I am going to clean that PSU up real good as a first priority.)



Cheers, Finn Hammer
Last edited by Finn Hammer on Mon Nov 20, 2017 3:51 pm, edited 1 time in total.
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Richard Hull
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Re: Fusor progress, Finn Hammer

Post by Richard Hull »

You will not see...or...should not see a neutron pulse at 100 milliseconds, (100ms/div). I hope you mean 100 microseconds/div (100us/div).

If the latter is the case then.....Yes!!....You are seeing cosmic ray based neutron events, probably neutrons surviving the plunge from 11 miles up where neutrons abound from starring cosmic events. Most are absorbed/scattered in the water in the lower amosphere. Some fast neuts are created at lower levels by starring events with cosmic rays that make it through the upper atmosphere.

I get 5-8 neturons per minute here in may lab on a regular basis with my super 3He 4 atmosphere detector. Thus, your smaller volume detector seems to be perfect and right on the money. It appears that inspite of you kludged up mess of connections you are, indeed, counting neutrons!

All the best making this real pretty and clening up the mess. Do not mess up in clenaing up. You have a working system here.

To all else reading this..........If your, supposed, electronic neutron counter, regardless of type, and, you are located at or near sea level, you had better not measure over 10 cpm neutron background. The foregoing assumes your counter system is not better and more sensitive than mine or Finn's.

If you read much more than 10 CPM you are counting noise of NORM. (Naturally Occuring Radioactive Material)

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: Fusor progress, Finn Hammer

Post by Finn Hammer »

Richard,

You are right.

The division is 1mS per div, and the pulses settle in at 500µS

Cheers, Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Richard Hull »

My professional preamp gives me neutron pulse widths of about 4-20us, depending. I am not familiar with the Russian tube's time constants. I bet that nasty old 100meg resistor is the culprit! This is a function of and demand made upon the user of the Russian tube. I have commented on this before.
That resistor forces the giant pulse widths. Still, a fine and suitable neutron detection though. However, the count rate is severly limited by this fact. I have further noted that this count rate limitation might not impact the average fusioneer for a number of reasons which I have enumerated.

Again, it sounds like you have a good counter there and, based on your background report, it is working fine.

It is nice you scoped the output. This is the first report I have seen from a Russian tube, operating properly, that has forever informed me that all using such a tube will experience rather long pulse widths. For me, this is a real eye opener and important data for all who are wise enough to see its implications.

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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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer »

Richard,

Ok, cool. I will try to reduce the value of that resistor, along with the supply voltage to see if it makes any difference. Obviously there is a nasty time constant in there somewhere.

I was reading about pulse pile up in one of the publications that Carl Willis pointed out, and there are preamplifiers that can pick up a pulse from a whole chain of piled up pulses. I will have to dig it out and reread it. Something about current sensing amplifiers or something like that.

Cheers, Finn Hammer
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Richard Hull
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Re: Fusor progress, Finn Hammer

Post by Richard Hull »

I am more than ready to believe the high value resistor is a demanded function of the Russian tube type to work as a quencher. If so, it is not a real issue as the tube seems fully functional and detecting real neutron events with it in circuit.

It is nice that you are willing to experiment with it. However the minute your count goes up, such as to 10 CPM, you might just accept the 100 meg resistor as a given to the tube type.

"Pile-up" is not a real issue in my system with it's short pulses. This is probably the difference in a $2000.00 detection tube and pre-amp and the in-expensive Russian tube's normal operational characteristics. It is just that the Russian tube might suffer plie-up at very high count rates, rates that the average fusioneer may never see or approach. I have used a rule of thumb of 10 to 1 ratio. If your pulse count rate time frame is 10 times the pulse width, pile-up will not be significant. A 500us width would allow a 5ms rate or 200 cps/12,000cpm count rate before pile-up is an issue.

You and I are currently on line and this is good as you are reponding more or less in real time.

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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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer »

edit: It is late, getting units all mixed up, gotta go to bed

But my goal would not be to increase counts per minute, it would be to shorten the pulsewidth. 500µS pulsewidth would allow (edit: 12000) counts per minute, and since they probably will not come flowing like off a clock generator, fewer.



I am not at this point able to know what that means, I am only just starting to work this aspect of fusor work, and the calculations related to neutron per minute out of a fusor is still black magic. But I will get there eventually.

Cheers, Finn Hammer
Last edited by Finn Hammer on Mon Nov 20, 2017 4:31 pm, edited 1 time in total.
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Re: Fusor progress, Finn Hammer

Post by Richard Hull »

I updated, edited my last post. I do this a lot as I think. check it out. I figured on 12,000 cpm as the max count for a 500us pulse width based on my self-arrived ratio of 10 to 1.

Pile-up is a big issue with GM counters or any detection method where the pulse width approaches the width, in time, between real detection event occurances. This ties into the physical "dead time" of the device quite outside of the time constants of the counting electronics.

As an example, you can theoretically change the input capacitance and resistance to a GM tube such that a scope will show a pulse width of 20us. However, even a super well quenched GM tube has a physically determined "dead time" of 60-100us. during this tuime period a second pulse will not be detected! Thus, in this case the dead time rules and the maximun count rate is dead time limited and not pulse time limited.

I am unaware of a published dead time spec on these Russian tubes. As such, a quest for shorting the electronic pulse width might mean nothing at all

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: Fusor progress, Finn Hammer

Post by Silviu Tamasdan »

As an anecdotal fact, the pulses I see with my corona tubes setup are 30-40us.

As for moderator, yes I noticed HDPE tends to be expensive. I have cut mine from restaurant-grade cutting boards bought from Amazon (look for the 1" thick ones) as they have tended to be the best bang for the buck I found. Then I discovered that motor oil works well as a moderator, and since I always have quite a bit of it around I have added that to my moderator stack. It works because it's composed of carbon and hydrogen same as HDPE, parrafin etc.
There _is_ madness to my method.
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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer »

Richard, Silvio

Thanks for your usefull input, it helps me to focus on what is possible and desirable, and to spot it on sight.

I lowered the voltage to 1600V and suddenly the counts changed to this much more desirable profile:

Notice the setting: 2µS / division.
2µs.png
Much like the difference between hitting the gong with a sledge hammer instead of tapping it with a teaspoon.

The sensitivity dropped to 1-2 pulses per minute.

I am still struggeling to get the supply to remain stable and ripple free, and don't see this as the final word, so I will remain quiet for a while untill I have some conclusive data to show.

Sitting in front of the scope, counting to between 30 and 55 seconds to time the cosmic hits (will they still come with this setting, how is it going to look?) reminds me of an old Zen story:
A grain of salt wanted to know how salty the oceams were, so it jumped in, and became one with the water of the ocean. That way the grain of salt gained perfect understanding.

Cheers, Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Richard Hull »

Great work Finn! with pulses like that, you might get a regular counter to run it and accumulate for 20 minutes and take the average. My ten minute averages of 5-8 cpm using a tube with about 2-3X your volume sounds about correct. Many really good frequency counters have a count mode on their range knob.

I have several HP 10-50mhz counters purchased over the years. All have a count mode and a pushbutton for start and stop. (reset) I would hate to have to count scope pulses over that period. I have counted as low as 3 cpm and as high as 12 cpm over single minute intervals. The average always comes in between 5-8 cpm. During a significant solar CME, I have seen the local count double, and during the most massive of CME's, triple! That big one brought the aurora as far south as Richmond.............36 degrees latitude.

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
Peter Schmelcher
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Re: Fusor progress, Finn Hammer

Post by Peter Schmelcher »

Finn I tested the same tube without any moderator (at sea level) some time ago and decided on proportional operation by using a 1000 volt tube bias.

One drawback you can see in the scope capture is that the neutron pulse output amplitude is smaller so shielding the electronics becomes more important.

The benefit I believe is the physics of proportional tube bias does not have a recovery time.

When you put a moderator (I used water) around the tube the initial kinetic energy gets stripped away before the neutrons enters the tube and the scope capture shows a more uniform tube pulse output (band) which you can use to amplitude calibrate your system. I do not have a scope capture with a moderator for this tube but you can see the band in the last scope capture.

The attached paper "Neutron flux variations near the Earth’s crust" pdf has a graph of neutron count rates verses altitude.

Have fun
-Peter


3 minutes 1800 volt bias
CN19H 3min 1800V.JPG
3 minutes 1500 volt bias
CN19H 3min 1500V.JPG
3 minutes 1000 volt bias
CN19H 3min 1KV.JPG
1 hour 1000 volt bias
CN19H 1hr 1KV.JPG
Attachments
HE3 tube nhess-3-637-2003.pdf
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Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Finn Hammer »

As I was walking around in the local recycling facility, also known as the scrapyard, my eyes glued themselves to a machine chassis sitting on the top of a 30 foot container, and I couldn't pass it up, because it was the perfect size. It is gross overkill, but I like that, and who can argue against a 50$ machine chassis?
Main view of future fusor layout
Main view of future fusor layout
The presence of a chassis also prompted me to get around to performing another much needed task, the welding of a KF25 flange to the foreline of the diffusion pump.
foreline connection to the diff. pump
foreline connection to the diff. pump
Another hurdle was the foreline trap. This is how it turned out:
The homemade foreline trap
The homemade foreline trap
This trap is filled with knitted wire mesh, which I have in abundance. I use it to make faraday suits:
Faraday suit when hit by 70kA strike
Faraday suit when hit by 70kA strike
It is another story with the Faraday suit, but this one was tested at a windmill wing test facility, where they hit it with 70kA, and it stayed intact much to my own surprise, I thought it would have evaporated.
Anyway, the mesh was coated with some sort of lubricant from the manufacturing process, so I washed it out with mineral spirit (turpentine, right) and baked it with my 500deg C heat gun. This created a smoke exhaust like a small vulcano for 10-15 minutes, then it faded away, and I think the filter is fine now.
Perhaps with outgassing, perhaps due to a leak, it pressure rises by 2microns per second when I isolate it from the pump, but future leak tests will tell what is the cause. The pump is a good one, it goes down to 2 microns right at inlet, and with the filter mounted, 5 microns, so no real problem here.
Butterfly valve bypass
Butterfly valve bypass
Calculating conductance is not yet my province, (but I am following Michael Bretti's thread closely, Thank you Michael) so in case the 4 inch butterfly valve is unable to close down with sufficient precision, I have added a bypass KF25 bellows valve so that I hopefully can get good controll of the deuterium flow into the atmosphere.
Merering side
Merering side
As you see on this picture, the metering will be taken care of, by a 50 FS Micron Baratron for fusion pressure monitoring, and a 901P for the pre fusion pressure, prior to deuterium admittance. The white stick on the picture is a bar of Macor, which I will machine down to hold the extension from feedthrough to the Grid.

Sadly enough, this is going to be the only progress for quite a while, since I am moving to a new house that needs work, and this will take all spare time for half a year at the least, but who can argue against getting this view, only 60 steps from the front door:
View 60 steps from my new home.
View 60 steps from my new home.
Cheers, Finn Hammer
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Re: Fusor progress, Finn Hammer

Post by Richard Hull »

Pausing fusion effort for making a livable abode in such a natural environment is a good cause. Good luck on getting things fixed up to live among nature.

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
Rex Allers
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Re: Fusor progress, Finn Hammer

Post by Rex Allers »

Nice work, Finn. Good wishes on your move.

Rather OT for fusor, but your faraday suit image reminded me of this from the old silent movie, Metropolis.
metropolis-lady.jpg
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Re: Fusor progress, Finn Hammer

Post by Dennis P Brown »

Finn, extremely nice chamber and impressive build for a fusor so far.

You might want to consider for the chamber vacuum gauge, a wire mesh screen at its entrance to prevent the plasma from interacting with interior electronics of that detector gauge. This arrangement works extremely well for my gauge (previously, I had major issues.) Also, metal support structures always require a good, independent ground to be on the safe side (I use two independent grounds for my fusor system - two standard wall outlets ground points (each on a separate circuit) and one to a water pipe.) That way, the star system handles the electronics/transformer and I have another grounding point used by the fusor body (connected in three places to handle o-ring issues) and master power supply cabinet as well as its cable.

I too live in a very rural area and despite my extreme commute, have to say (at least for now), well worth it living in the woods near a lovely stream in an even more lovely valley. So, I tend to agree that your delay is well worth that end result - besides, it will give you time to consider issues for a fusor you might have overlooked.

As you will often sign off, cheers.
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