Fusor Producing and measuring Neutrons

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Dennis P Brown
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Fusor Producing and measuring Neutrons

Post by Dennis P Brown »

I finally got the required HV cable, and throwing caution to the wind, installed the CSA preamp with my new NIM box neutron detection electronic system and powered everything up for a full neutron test using my fusor. I very slowly adjusted the voltage on the CSA - both up and down.

The scope was set to 2 volts/Div; the time scale 20 usec. The 3He tube was used and was set to around 850 volts. Deuterium pressure was around/near 20 microns. The fusor power was set at 31 kV and 28 ma. The TC 426 Gain was set to 50. The device/cable setup is exactly as Richards diagram in the FAQ NIM post (Neutron detection topic.) I added an oscilloscope to the chain (reading the output from the main amp.)

The count rate/sec on the panel with a modulator was 5300 and without was 1500 (also the noise floor.) Further, the neutron signal tracked nicely with fusor power (current) - that is, as I dialed the current down, the count rate went down (voltage was held fairly constant.) Of course I did the removal of the modulator and the count went to the noise floor but returned to full level with the modulator reinstalled.

The Geiger counter was indicating no measurable X-rays (compared to its BG counts.)

Well, I think all is operating correctly. I did want to try the new 3He tube with the NIM and pre-amp. And now that appears successful.

I do need to find the optimum voltage for the 3He tube (I have no spec's on it. The system it came with was turnkey.) Just selected a somewhat arbitrary value that I knew was in a safe range. Then I need to properly test the TC 426 amp to see if its SCA function works. Then I guess I want to try my Boron-10 detector (it needs a lot higher applied voltage: 1750 - 2300 if I recall correctly.)

Its been a number of years since I ran the fusor for real - a while back I obtained a 3He detector system but it (primarily the software) did not appear to work. So I decided to go the NIM route, add a pre-amp and use the 3He tube with my fusor. After a lot of minor set backs (esp. the CSA preamp), the 3He tube appears to be working though the noise level (expected) needs to be addressed.

The deuterium pressure controls current in a precise manner. I can set any voltage from 20 kV to 31 kV. So, very pleased with that part of the setup. Now if I can get all the detectors to operate in a similar manner I can consider future projects.

I will say using a NIM system is far away easier then a 'turnkey' black box system when it comes to diagnosing issues when they occur. Certainly a NIM is more complex but does offer a lot of insight into the entire system and allows isolation of specific parts and makes testing said systems rather straight forward. It does appear those systems are getting harder to locate and prices are fairly fixed so deals are hard to come by. Surprised Amazon sells the CSA preamp & board - wouldn't think that is a typical item that enough people would want.

I really do need to shorten the pre-amp "In" cable and add a proper connector so the noise floor will be lowered a good deal. But that is for another day after I get another proper HV cable (slow boat from China.)

Now that I discovered the original detector system's HV cable was trash I will also need to re-check that system to see if it now works (through the software is an absolute mess and still baffles me.) That is, after I do the afore mentioned projects. I may even start checking the PMT system again (Through that does not require the use of the CSA pre-amp - I have a PMT pre-amp (thank goodness.)

In passing - the fusor is behaving in a perfectly stable manner. Once the plasma is ignited the system remains completely constant and requires no adjustments/baby sitting. The chamber is holding vacuum with only very minor out gassing so it is and remains very clean.
Attachments
Fusor Setup (Grey cable goes to the Scope)
Fusor Setup (Grey cable goes to the Scope)
Power Supply/values
Power Supply/values
Neutron Count no Mod.
Neutron Count no Mod.
Neutron Counts/sec with Mod
Neutron Counts/sec with Mod
Neutron signal on Scope (from CSA & TC 426)
Neutron signal on Scope (from CSA & TC 426)
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Richard Hull
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

Interesting run info. Of course the two count differentials were both noise and not verifiable neutron counts. There is not the remotest possibility of any thousands of CPS being recorded with neutrons involved in any way. I am not saying there were no neutrons. I am saying there was no verifiable neutron detection.

I assume what you call a modulator is actually a moderator.

The pulse looks good on the scope but the counts are insane and are all 100% noise.

There is so much we do not know here.

A complete image of your 3He tube and its specs would be nice. 4 ATM or unknown? It is common for 4 atm 3He tubes to need up to `1400 to 1600 volts.

You need to hook your system up with the tube attached to the preamp and scope only the preamp out. put the scope on 2 or 20us/div and the voltage to 20-50mv per division. Using no source near the tube in its moderator. You should see no more than 5-15 pulses per minute! if not you may have to adjust your trigger level control on the scope. I assume your scope is not a DSO and can't be set to capture a single pulse. You will have to watch the scope like a hawk to see those rare pulses over the minute time frame.

In a well adjust neutron counter system you might see 5-10 counts per minute and at 30kv at 10-15ma maybe 1000 cpm perhaps more, perhaps a bit less. Tube voltage is critical There is a point where the preamp will just start showing a few pulse per minute due to cosmics.

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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Dennis P Brown
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Re: Fusor Producing and measuring Neutrons

Post by Dennis P Brown »

Sorry about the moderator (some one will need to do that for my posts ... well, actually you did ;) ) and modulator - I always type out the post and don't pay attention as long as the spelling/grammar appear correct.

I have a picture of the entire set up. The next image is a close up of the 3He tube (CHM-32.)

I did look at the CSA with just the 3He and connected to the scope as you instructed (tried 1400 - 1700 V) - I saw all of one large pulse during the entire time but nothing else over 5 minutes. However, I noticed the tube was extremely sensitive to me making contact with it (voltage spikes) - whenever I touched/handled the detector tube (while charged) in any way; in fact, the scope showed huge noise signals - I guess the CSA really see's those micro-charges/ground potentials.

So I decided to enclosed the 3He detector in a metal tube (no electrical contact) and this cleared that issue up. Then with the tube powered to 1500 volts, and in the modulator, I did see the system trigger four to seven times per minute (the scope) and the rate meter would swing up momentarily (lowest setting of 1 count/sec.) Was this what you where suggesting?

I did retest the CSA with the pulse generator and its response is still fine. Then I added the TC 426 and all looks ok but I will say that the Gain levels are certainly not accurate* on the TC 426. The '100' gain level is more like 60 and the 10 is like 6, etc. (turns out this problem/issue was simply a chip pin oxide and/or chip seating issue and extremely was easy to fix. See note below.)

The SCA function does not appear to work - I put in a spike pulse and it didn't appear to respond. I will look into that later.

To get an idea of what might be going on with possible noise sources, I ran only the powered CSA box with just the pulse generator and fired up the fusor. I then ran the fusor with the full plasma - 30 kV, and 28 ma; and there was zero noise appearing on the scope - just the standard spikes matching the swings of the pulse generator. In this test the detector was not connected. Only the pulse generator but I did want to see if the fusor was causing major issues to just the CSA unit alone. Apparently it isn't.

When I included the TC 426 amp in the chain, the display with the fusor running did show some noise (scope settings; 25 mV/div - see image; I believe this is 60 cycle after adjusting and reading the time/div scale.) The pulse generated signal and the CSA/amp response (spikes) can be clearly seen along with a sinusoidal type signal riding along - strangely, this sin function is a 'wave packet" and not continuous - strange. This level of fusor noise, I would think, isn't too dramatic but does show some significance at the 25 mV/div scale. I assume the 3He pulse would be significantly greater than that level and would not interfere with pulse detection?

However, when the turbo is running, the noise displayed on the scope is terrible even at the 50 mV/div. I assume this is generated via the common power lines since most the system is shielded?

The CSA is in a metal box (battery powered) and I use coaxial cable. In the past, I always used a diffusion pump and only very recently converted over to a turbo. That, appears to be a mistake. However, outside noise is a fact of life and with coaxial and filtering on the plugs, I am shocked that this is an issue that would swamp out the detector. The fusor contribution, as far as noise level, is small compared to the turbo issue.

* Aside: I noticed that when I pressed three specific chips on the board, the gain went up some (an old trick I learned trying to repair my avionics in my plane.) So I pulled each of these chips and re-installed them. The gain now exactly matches the displayed value. That is, the "100" gain was giving '60' but now gives "100" as it should. I checked the other values and they all now agree with the labeled gain. Wish all my issues were that simple!
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Fusor system
Fusor system
3He tube
3He tube
Fusor w/plasma @ 30 kV and 30 ma CSA & Amp; signal created via pulse Gen
Fusor w/plasma @ 30 kV and 30 ma CSA & Amp; signal created via pulse Gen
Last edited by Dennis P Brown on Thu Jul 21, 2022 1:23 pm, edited 7 times in total.
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Richard Hull
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

I think we need to dwell 100% on the tube and CSA (CR110) output here. No other components.
I am bothered by the Russian tube. I have zero experience with them.

Typically, with no known neutron source and no hot gamma source, you are left with only the detection of the occasional cosmic ray to see where the voltage setting for the tube is located when using a known good 4 ATM 3He tube and good preamp.

Typically, hot gammas rarely produce more that a fractional millivolt signal. Neutrons produce 2-5 mv signal and the average cosmic in much more potent right out of the preamp maybe 8-10mv.

Place the tube in the moderator
scope on the CSA output
start at 1000 volts bias and go up 100 volts at a time.
set the scope at 10mv/div and the time base at 10 us/div.
look for blips at the slow rate of 2-5 per minute.

You are at a disadvantage without a DSO scope as it will capture a single pulse and display it locked on the screen.

Remember a ratemeter like you have in the digital form (led readout) and analog readout (meter) is of no value what so ever in setup! They want a frequency in pulses per second. setup demands only two things. A DSO to capture a single pulse or a simple digital counter that will accumulate counts over time. many frequency counters and ratemeters have absolutely no control over the counting time interval. HZ position counts for second and then re-zeros in one second to count for another second. A simple digital counter when the count button is pressed it will count and accumulate pulses for an infinite period of time. (very valuable in setup) A DSO will see a pulse, based on its settings and trigger level setting and freeze it on the scope screen until the user presses reset and this kills the waveform and waits patently for the next pulse to display.

The above is ideal for seeing slow appearing cosmics, in that the count on the counter will not advance until another cosmic is detected on the simple digital counter.

Look carefully at the NIM counter/timer attached in the image. It just counts individual pulses over a user selected time from 1 second and then stops to 100,000 seconds and then stops. Very very useful.

In the end, it is all about pulse voltage levels, NIM signal levels are demanded for this counter timer to count. This is why we amplifier weak signals that are to be counted.

I really hate to dump all this bad news on you. with a DSO you could stop the rare pulse and examine it. With a good counter you could amplify the CSA output and count those rare cosmics to be able to set the hV level properly. This is a must have starting point if you have no neutron source and no hot radium or U ore sample.

it is tough to visibly see a 5us pulse on a common oscope.

Richard Hull
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Nim Conter.anno.jpg
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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Dennis P Brown
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Re: Fusor Producing and measuring Neutrons

Post by Dennis P Brown »

Well, a capture scope is necessary then I'll see if someone I know can lend me one; I do know a few people that do electronics. If I can get such a scope, just I will repeat the cosmic ray discovery method.

The noise issue is beyond troublesome since fixes are tedious and failure masks any possible signal. The fusor does produce neutrons but as everyone with such a device, a lot of noise as well. I am concerned that the NIM box devices also pick up that noise (to some extent.) Still, I will try your ideas and see what I can determine.

I have a digital counter that works well for Geiger tubes and has an input for a scintillator (I have one but only for gamma). I will revisit my fast neutron PMT; a lot of issues there but will try a work-around, first.
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

The single pulse capture on a DSO is easy to use, but if someone lends you the scope, make sure they show you how to set up the single pulse capture feature.
I love to set it up with the time base to see a 60hz pulse.
start by doing the following set the time base to 20 millisec/division and the vertical to 1 volt/division.
take the probe in hand and touch the tip. The house wiring will induce a 60 hertz signal on the screen
adjust the controls while the signal off your hand is there. so that the sine wave is nice and pretty and relatively stable.
Set the DSO to a trigger level well within the waveform's voltage range above the zero axis.
set the DSO to single pulse capture mode.
tap the probe tip for an instant.
You should have a locked down capture of the waveform from the first millisecond or two of your finger tap.

Once seen, the true value of a DSO shows itself brilliantly as this can capture a sub-microsecond pulse as easily as a 60hz 16 millisecond pulse.

Modern $250 brand new DSO tutorial and demo.
https://www.youtube.com/watch?v=mIoHFwyeE44

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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Richard Hull
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

If you are to follow the 3He tube into neutron measurement, it is key to first verify it can be biased to see either gamma fuzz, high energy cosmics or real neutrons and see these in isolation as separate entities out of a good preamp. Only then will you be able to move to the next NIM stage of amplification and discrimination processing of them.

Any other method of neutron detection is far less desirable and more filled with probable misinterpretation of results by the untrained.

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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Dennis P Brown
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Re: Fusor Producing and measuring Neutrons

Post by Dennis P Brown »

Till I get a storage scope, I've decided to revisit my old PMT system. I will certainly ask for training with a storage scope if I locate one because they are certainly a mystery to me as far as operation!
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

DSOs are identical to a common scope. They have lots of cool features which you do not have to use. You can grow into them as needed. The one easy feature to use is the button operated single pulse capture feature.

Once the single pulse mode is chosen in the trigger menu, the scope sits there mindlessly showing only a zero trace line forever until a pulse occurs that triggers the scope and, boom, there is your pulse. You can fiddle with the time base and vertical voltage controls to enlarge and expand it for better full screen viewing. Once you have it the right size, you hit the reset trigger and again the scope goes blank to a zero line trace until the next time a pulse triggers and then it is locked down. Drop out of the single event or pulse mode in the trigger menu to normal or auto and your old stock scope is back.

The trigger menu on a DSO is one of the most useful of all the menus that seem so daunting to the new user. You need not know more than how to use the trigger menu at first. the DSO has a nice line feature that lets you see where your trigger level is set when turning the trigger control.

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 Producing and measuring Neutrons

Post by Matt_Gibson »

My Siglent 50Mhz digital scope was around $200 (used on eBay) and has been a lifesaver on my projects (non fusor so far). Very easy to use/setup.

-Matt
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Re: Fusor Producing and measuring Neutrons

Post by Finn Hammer »

My life changed the day I finally bought the first DSO, a Tek TDS210.
I went througt 2 of those, then went on to a 4 channel colour TDS2224.
I now own 2 RIGOL DS1056Z, one for the electronics lab, one for the service trunk.
Before that, I struggled to get a triggered trace on a Tek 845. It was by then it dawned on me, something I already knew from the mechanical world: the master can get away with creating his masterpieces with the simplest of tools, the newbie needs state of the art tools to lift above the mediocre.
Realizing this, I bought the DSO and things got a lot easier.
An oscilloscope is like an electrical microscope, the DSO variety as equipped with a camera. You need it.
Would a biologist study his fungus using a magnifying glass?, perhaps. But he would be advancing his art with a proper microscope.
Best money spent in this hobby.
End of rant.

Cheers, Finn Hammer
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Richard Hull
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

In 1995 while doing work with Dr. Peter Graneau on Water arc explosions that would result in in a peer review article in the Journal of Plasma Physics, I was forced to purchase a DSO. At this time, Tektronics was making modern DSO's with CRT displays. I bought their 60mhz model for $2400. It hurt, but once I employed it in capturing the 1megawatt impulses from these explosions, (3000 amp peak currents), I just stopped using my two other TEK analog scopes. They became somewhat worthless. Within 5 years Tek introduced what we engineers dubbed their "lunch box" series of DSO's so common today.

I spent the long buck again and bought their 2 channel 60mhz model for $1100. Now I have a total of 5 DSO's here. Like most pioneers, I paid dearly for being among the first DSO users. I bought an early FFT add-on module for my early TEK DSO for $595. Now for $300 you can get a complete 100mhz DSO that has a ready to go FFT mode in it for exactly half that lone module.

In short, your first scope must be a DSO

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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Dennis P Brown
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Re: Fusor Producing and measuring Neutrons

Post by Dennis P Brown »

I agree a storage scope is the only way to go; guess I keep an eye out for a good deal on ebay. Why is an FFT option useful relative to fusor work?

This unit is new but is it useful? While a 'storage scope' with a display seems rather inexpensive. Yes, the Chinese are making some very low cost and useful items but what's the catch here?

https://www.ebay.com/itm/164273276679?v ... ec947e4781
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Richard Hull
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

I would get one with formal knobs and look for a single step, single trigger or such button in the trigger area on the front panel.
This flat screen may be fine. I am not familiar with it or its ilk.

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 Producing and measuring Neutrons

Post by Matt_Gibson »

I remember very vaguely being deterred from those flat screen type scopes. Not sure why, so you might want to do some research before passing.

A good scope will be just as valuable as a good power supply. I’m very much a novice when it comes to most of electronic engineering (Electric utilities for me) so it’s been invaluable to be able to scope something and show the real pros what I’m looking at. I like to think of it as a translator…

I recently had blown $100.00 with of MOSFETs on a Class E musical Tesla coil. After getting crap CS from the company, I was able to resolve by showing my waveforms to some pros on a forum. No more blown MOSFETs and nice music now!

-Matt
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Richard Hull
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

I did not speak to Dennis' query regarding FFT in fusor work. It is not important. Fast Fourier Transforms work in a time domain analysis and make possible frequency analysis in what sometimes seems a jumble of RF signals. We tend to use it in Spectrum analysis. It is of no value for normal fusion system work. Electronics engineers especially those dealing in noise analysis find the FFT function in a scope a godsend.

Back in the 90's I needed it for one investigation I was involved with. I have not needed it since that time.

For a deep dive that will leave your head spinning read what Wikipedia has to say about FFT.

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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Dennis P Brown
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Re: Fusor Producing and measuring Neutrons

Post by Dennis P Brown »

Thank you Richard for both this information and the FAQ thread on scopes - certainly needed for those in transition - i.e. from basic novice relative to fusor detector electronics into someone attempting more advance work in that rather interesting field.

I ordered a scope that has knobs because you are correct, far easier to master; still being a storage scope it has menu's and selection buttons and does far too much; meaning - steep learning curve. But that is the price one now pays for high performance scopes that cost little but try to impress by doing everything. Wonder if it will mow my lawn?

Your pic's of the scopes brought back memories (I've used them back in the 90's and have forgotten 99.9732% of their operation. Kind'a like I've forgotten proper use of significant digits in data ... .)
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Richard Hull
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Re: Fusor Producing and measuring Neutrons

Post by Richard Hull »

The DSOs are no more complex than you need them to be. As simple to operate as a common old scope but with fewer knobs and such. Menus allow for all the old adjustments related to triggering, etc. However, a vast new world of capabilities lies below the surface in the menus that are handy and never available in the history of mankind! Use only to the level of your ease of use and need at first. Much later, once comfortable, you can go exploring based on the scope's manual.

Note: Once you get the scope setup the way you like it....Save the configuration! (you can save a number of them) You can then if befuddled in roaming about the menus, instantly re-store all the scope settings to you favorite newbie state. Ain't that great! It has pulled my ass out of a self-wandering, scope menu created, funk many times. A home base, if you will.

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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