Joe Gayo's lab tour

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Scott Moroch
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Re: Joe Gayo's lab tour

Post by Scott Moroch »

I was interested in your 7-hole grid design. The models support the observations.

Simulation Video: https://www.youtube.com/watch?v=P5lp3Wu ... e=youtu.be

Initial distribution is circular, launched from the left with 0 KE. Grid at -60kV with respect to the chamber.
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Rex Allers
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Re: Joe Gayo's lab tour

Post by Rex Allers »

So PIC simulation is new to me. From a little searching I assume this is
particle-in-cell computation, a method for simulating plasma.

This wiki covers the basics -- https://en.wikipedia.org/wiki/Particle-in-cell

Looking at your plot in the youtube link, it seems the simulation only represents a quarter of a slice through the whole device. Symmetry means the fields in the other three quadrants are just mirrors of the one calculated.

Not needed, but I captured one frame from your video and did the mirroring of the main plot window, so the field in the whole device would look like this.
PIC sim full.png
I assume the elapsing time as the video plays reflects actual time for the plasma to evolve in the chamber. Does the simulation give the actual time represented across the video?

I have one small question about the voltages. You said the chamber was at 60 kV. Looking at the sim plots, the two edges that seem to represent the chamber edges appear to always be at 50 kV. As the fields evolve some areas get up to 60 kV but those outside edges are still at 50 kV. Does this mean the external excitation voltage applied is 50 kV?

What software did you use to run this?

Thanks for sharing.
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Carl Willis
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Re: Joe Gayo's lab tour

Post by Carl Willis »

Joe, this is a top-flight effort, and I am thrilled to see what appears to be a novel paradigm in fusor efficiency developing in your work.

The regime of high pressure, small electrodes, high potential, and high neutron yield is undoubtedly a new domain worthy of further attention.

Have you provided a detailed discussion of your electrode geometry on this board? I apologize if I missed it; I have mostly been away from the forums the last few years. But it's progress like this that will make me come back!

Thanks for sharing your impressive project here.

-Carl
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Joe Gayo
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

@Rex Yes, in this simulation the applied potential difference is 50kV. You are correct about the symmetry of the simulation as well. The animation represents microseconds. The software is Starfish (https://www.particleincell.com/starfish/ - Free!)

@Carl Thanks! The electrode geometry is discussed in my lab tour video on YouTube. I'm constantly refining the electrode geometry based on simulation and testing. The next "knob" to turn will be material selection.
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Re: Joe Gayo's lab tour

Post by Jon Rosenstiel »

Joe,

Awesome work, and congrats on the ultra-mega neutron numbers, you are the man! After many, many years the baton has finally found a new home... about time! And you didn't just up the ante a little bit, you blew it to smithereens!

In your video you mention that your device's neutron output on axis with the plasma beam is about 2 times that of the neutron output measured at right angles to the beam. As your device is not truly isotropic in neutron output it may be more accurate to quantify neutron flux in neutrons/sq-cm/second.

Jon Rosenstiel

PS: Anyone have a foot or so of 4" x 4" 6061-T6 bar stock they wanna part with?
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Re: Joe Gayo's lab tour

Post by Dan Knapp »

In regard to the PIC simulation, please be advised that a 2D simulation does not give a valid representation of a system with axial symmetry.
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Richard Hull
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Re: Joe Gayo's lab tour

Post by Richard Hull »

With the 4 X4 6061 request from Jon, coupled with his machining abilities, I imagine he has ideas. I am still musing over using my 6 way 2.75 CF cross to replaced fusor IV.

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Re: Joe Gayo's lab tour

Post by Joe Gayo »

@Dan Sure it does ... it's an axially symmetric (RZ) code/solver. I actually, know the individual that wrote Starfish (his Ph.D.) and he and I are working together on simulations.
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Re: Joe Gayo's lab tour

Post by Dan Knapp »

The description on the link to the Starfish code describes it as a 2D simulation. I overlooked the mention on another page that it allows the selection of a Cartesian or axisymmetric system, which requires a more sophisticated RZ solver. I guess I was surprised that someone would be making the more sophisticated software freely available. I stand corrected. My apologies.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

@Jon - Thank you for the kind words and the tour of your impressive lab!

@Everyone -
I have a -100kV @ 20mA power supply arriving in the next few weeks and will begin experimenting with different cathode/anode materials. Based on some preliminary results the Aluminum construction may be contributing to the strong results.
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Scott Moroch
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Re: Joe Gayo's lab tour

Post by Scott Moroch »

Joe,

Your effort is really impressive and it definitely shows in the numbers. There has been a lot of talk recently that these smaller fusors are capable of outputting a higher neutron rate, for a given kW input, than larger 6-10" devices. Intuitively, I am on board with this. However, up until your efforts I have not seen extremely convincing evidence that such claims are true. I think this opens up the opportunity for a community wide effort to collect more data. In particular, I am suggesting that all members with an active fusor attempt to contribute to a community-wide data log, as was attempted here:

viewtopic.php?f=47&t=11331

I have compared your output rates with the other data collected so far and it is clear that they are outliers (qualitatively). I would certainty be interested in seeing your neutron output rate for 40-50 kV and 5-15 mA; as few other fusors have the ability to reach 70 kV so comparison is difficult.

Can't wait to see what you do next.

Scott
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Joe Gayo
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

I'm still collecting data (the chamber is still improving with loading and vacuum quality), but here are some general results:

60 kV, ~1M n/sec/mA (16.2M at 15mA, Q = 2.11 e-8!), 25 mTorr

I created this video to record results at 5mA (40 - 60kV), 22mTorr. https://youtu.be/1MLFN8FKvZc
Performance @ 2.9 Pa D2.png
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Richard Hull
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Re: Joe Gayo's lab tour

Post by Richard Hull »

Super video!

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Fusion is the energy of the future....and it always will be
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

My -100kV @ 20mA power supply arrived on Friday ...

Several Observations -

- The chamber can support 90kV (so far ... more conditioning may improve)
- I measure about 2E+6 n/sec/mA at 90kV ... multiple 3.6E+7 runs (90kV, 18mA, 19 mTorr)
- Need to reposition detectors as not to saturate (110 bub in 6 seconds, 12.7 cm)
Lukas Springer
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Re: Joe Gayo's lab tour

Post by Lukas Springer »

Your most recent graph shows some "oscillation" / quantized steps, any Idea as to where this comes from?
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

@Lukas - If you are talking about the small oscillations that follow a trendline, then this is a result of the statistical nature of neutron measurement. The counts are averaged over 500 msec but I only report rates that have been averaged over 5 seconds or more and not a single measurement spike.

@everyone - Above 90kV I'm having a saturation (maybe?) issue with my detector where the counts increase asymptotically and the numbers become very high. Is this because of a lack of deadtime? I would assume it would stop counting if the BF3 tube just constantly discharged because the signal would be constantly high. Or is it saturated but there is enough of an AC component to the current that it's registered as erroneously high counts? I need to set up an additional detector at a greater distance...

I have tried reducing shaping time (which seemed to help) on the amplifier to allow higher count rates. With a shaping time of 4usec, I would think it would support many kHz of rates. The detector seems fine to 3 kHz count rate.
Last edited by Joe Gayo on Mon Jul 01, 2019 8:07 pm, edited 1 time in total.
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Re: Joe Gayo's lab tour

Post by Lukas Springer »

Damn statistics, ruin everything! :D

That sounds like signal pileup in your detector, have you tried just using a higher distance to your reactor?
faster shaping can do only so much and most gas proportional detectors are not made for high counting rate.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

Yes, I’m going to set up an additional detector at a greater distance (The present detector location is calibrated and gives nice resolution for low current/voltage operating conditions), but I was curious about typical resolving time for a BF3 detector system. I could setup a signal generator to test. I would think dead time issues would reduce the count rate, not increase (I found a paper citing dead-time under 10usec).

https://www.tandfonline.com/doi/pdf/10. ... 96.9732021

Another question: I understand how pile-up can distort spectroscopy measurements but in pure counting situations how does the count rate multiply?
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Re: Joe Gayo's lab tour

Post by Robert Dwyer »

I think there should be decent dead time in your system that can cause pulse-pileup, but I am unsure why that would make you have multiplying count rates. I think there are three places that will give you dead time, and measurements of these with an o-scope could help diagnose this issue:

1. Tube dead time: This stems from the recovery period due to the voltage drop across the tube when a current flows from a pulse. The current needs to drop far enough so there is sufficient voltage to cause a large enough pulse to be formed for the amps and shaping electronics to detect the event.

2. Electronics Dead time: This will come from the any NIM or other electronics used for pulse shaping and analysis suhc as amps, scas, etc.. there is a time were the electronics are busy with a single event and cannot resolve any other inputs that come into the electronics. On many NIM modules there is an output on the back labled 'DT' which sends a logic signal while the module is busy with an even allowing you to better track deadtime on the electronics front.

3. Scaler Dead time: I am putting this in a different category than the 'electronics' category, as it has less to do with pulse shaping, but more the counting end of thing. This could include hardware such as physical counters or scalers, but also could extend to digitizers, mca's or even software, that adds deadtime to the system were, at high count rates, pulses may be lost.

As your tube is a gas tube, I think Lukas is right in suggesting most of your issues are stemming from the tube itself (if it is a pileup related event). The deadtime, if not found on manufacturer's sheet, can be measured using an oscilliscope. Setting the oscilliscope to trigger on a pulse from the detector each event, but not clear the screen. After about 50-100 pulses, you should see the time between the pulses (dead time). There are many mathematical models you can find that have been done on correcting for dead time, but the easiest way is to move the detector farther back. These models, and more in depth explanations of dead time can be found online. I suggest Glenn Knoll's book which is great investment for both the hobbiest and professional interested in radiation counting, as it explains things far more in-depth and better than I ever could.

Below is an image showing both the dead-time and recovery time in a geiger tube, which will be similar to what is probably happening in your tube.
Dead_time_of_geiger_muller_tube.png
The dead time should keep you from seeing too high count rates. If your tube is not properly quenched, then perhaps there may be an issue there. If there is nothing erroneous in your dead time measurments or pulse traces, then I suspect an issue with counting electronics such as your scaler. At 90kv sufficient noise may be entering your system as well. Both the dead time measurements and a farther detector will give you a good start as to figuring out this issue.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

I have a bubble dosimeter reading of 4.8E+7 which seems ridiculous...

@Robert
I have Knoll’s book and agree it’s a must. There are several things I’m going to investigate with the counting electronics (plus add the greater distance detector)
Last edited by Joe Gayo on Mon Jul 01, 2019 9:18 pm, edited 1 time in total.
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Re: Joe Gayo's lab tour

Post by Robert Dwyer »

Does this reading corellate with the high count rate from the BF3 tube? If so then you may be seeing real counts. I think setting up both a bubble dosimeter along with another tube at a greater distance at the same parameters of voltage, current, and pressure and see if you get the same yield. If the dosimeter is reading these results I think the likelihood of real events is true. At those neutron numbers pileup events would still be visible, but a trend should still be seen with the BTI with regards to a count rate.

If you do see evidence of these numbers being real, my next suggestion is activation of some kind. Silver, Rhodium, Silvers, etc... to verify these yields.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

Yes, but I want a lot more data. I’ve had some runs where the rates were much higher but unfortunately I didn’t have a bubble dosimeter present.

I’ve activated silver, indium, and manganese quite easily to many times background. The device can run at 5E+6 for extended periods (60 minutes).
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Re: Joe Gayo's lab tour

Post by Richard Hull »

I would take three routes here with large numbers you are apparently getting.

BTI at some increased range. (BTI dosimeter needs to be fresh and trusted, obviously.) If in excellent shape, different ranges should jibe based on inverse square law plus or minus a bit, but not to an extreme.

Silver activation - Always a true indicator of Neutrons. Should hold to some semblance of the inverse square law as well.

Definitely move the BF3 tube out farther. The suggestion about an o'scope picture of the preamp output is a must.... To eliminate the issue of noise. due to proximity. If I were there, I would be all over the preamp output with a good DSO like ugly on a gorilla. Electronic counting is tough and noise loves a home in long cables that are terminated poorly or not at all. Even with good technique, the energy and RF at 90kv in a fusor might be an issue. This is especially true if the moderator and tube are in close proximity to the fusor. If all is fine with the electronics its count at various ranges should obey the inverse square law just like the dosimeter. Neutrons, while they can scatter somewhat in air, have decent straight line ranges much like gamma rays over laboratory distances.

Sometimes I find I just can't do it all to a degree that make some of my efforts payoff like I want. I have knowledable friend in the HEAS here that I can call upon in critical endeavors, mostly in data gathering.

Much of the above that I have suggested should rely on a good lab assistant as you will have your hands full with controlling the fusor in the experiment. This is especially true for the multiple capture and saving of screen images on the DSO during the experiment. The lab assistant is almost a must have and should have some familiarity with the process and equipment. A third person could be a "step-and-fetch-it". Such a person need not have any experience, just a willingness to help the two researchers in whatever small intermediate tasks that are menial yet immediately helpful. (log book entries called out to him.)

I have even used a large cadre of very experienced fusor people at the HEAS gathering in October for a lot of tasks I fret over when alone.

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: Joe Gayo's lab tour

Post by Joe Gayo »

I'll post more details in the near future, but I was having issues of gamma/x-ray pile-up above 90kV. These normally low amplitudes pulses pilled up to such an extreme level that they crossed the discriminator threshold. This was resolved in the typical fashion with increased distance, shielding, and discriminator level.

I have re-validated the results below 90kV and my previous numbers stand. I have some new record results that I will be posting ...
Last edited by Joe Gayo on Mon Jul 22, 2019 5:32 pm, edited 1 time in total.
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Re: Joe Gayo's lab tour

Post by Richard Hull »

Indeed, X-rays get vastly more intense as the voltage advances. There is a trade off which Joe is helping to quantify here. His chambers are of low Z aluminum which typically reduce X-ray production, but at high voltages, what x-rays are produced make the chamber absolutely transparent to the higher energy x-rays that are produced. Interesting....

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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