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Re: Joe Gayo's lab tour

Posted: Tue Jun 18, 2019 5:15 pm
by Dennis P Brown
I too used a bubble detector to first determine that a smaller chamber does, in fact, lead to greater fusion. I did this about a year or so ago. I am glad to see this work taken further and with better accuracy. I agree with Richard, and why this also caught my attention for confirmation - smaller chambers (i.e. distance from cathode to ground and higher deuterium operating pressure) does result in significantly higher fusion rates. Your results are very good and effort outstanding.

Re: Joe Gayo's lab tour

Posted: Tue Jun 18, 2019 5:43 pm
by Dan Knapp
Joe

Can you explain your magnetic field plot? This appears to be a half image of the cross section of two ring magnets (that would also be cathodes?). Is this correct?

If so, it is not clear how you would get magnetic shielding with the field lines terminating on the cathodes.

Re: Joe Gayo's lab tour

Posted: Tue Jun 18, 2019 5:55 pm
by Joe Gayo
The cathode is in the center along the axis of the magnetic field (the plot is oriented vertically but the actual layout is horizontal)

(P.S. I'm working on a paper that I planing on submitting to a journal to discuss this system.)

Re: Joe Gayo's lab tour

Posted: Tue Jun 18, 2019 8:09 pm
by Robert Dwyer
Neutron counts into the 1e7 range with a smaller chamber! Wow! I never though I would see it. This is a great system. It is cool to see that you are using software like FEMM to investigate your fields. It would be interesting to see plots of the E-field in your setup as well.

After going back through my data and reading some articles, I had gotten the mindset that the high operating pressures were in fact hurting as the ions would collide with too many neutrals not allowing them to reach higher energies. It appears I was wrong. Perhaps these systems want more power (voltage and current) in the high pressure regime, or perhaps my old system was not clean enough to see the big numbers... Either way, great job.
Of course you also have that background field, who knows how much of these improved numbers come from each of things, or any combination of these things.

Re: Joe Gayo's lab tour

Posted: Tue Jun 18, 2019 8:21 pm
by Joe Gayo
How about a PIC simulation that shows the time evolved potential field:
https://youtu.be/wEO5Ewo_H_w (Note: The cathode is at 0V and the chamber walls at 50kV)

Re: Joe Gayo's lab tour

Posted: Tue Jun 18, 2019 11:30 pm
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.

Re: Joe Gayo's lab tour

Posted: Wed Jun 19, 2019 8:16 am
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.

Re: Joe Gayo's lab tour

Posted: Wed Jun 19, 2019 12:00 pm
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

Re: Joe Gayo's lab tour

Posted: Wed Jun 19, 2019 2:02 pm
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.

Re: Joe Gayo's lab tour

Posted: Thu Jun 20, 2019 5:08 pm
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?

Re: Joe Gayo's lab tour

Posted: Thu Jun 20, 2019 10:02 pm
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.

Re: Joe Gayo's lab tour

Posted: Thu Jun 20, 2019 11:37 pm
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.

Richard Hull

Re: Joe Gayo's lab tour

Posted: Fri Jun 21, 2019 12:27 am
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.

Re: Joe Gayo's lab tour

Posted: Fri Jun 21, 2019 7:42 am
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.

Re: Joe Gayo's lab tour

Posted: Mon Jun 24, 2019 6:21 pm
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.

Re: Joe Gayo's lab tour

Posted: Mon Jun 24, 2019 11:06 pm
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

Re: Joe Gayo's lab tour

Posted: Thu Jun 27, 2019 12:58 am
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

Re: Joe Gayo's lab tour

Posted: Thu Jun 27, 2019 3:20 am
by Richard Hull
Super video!

Richard Hull

Re: Joe Gayo's lab tour

Posted: Sun Jun 30, 2019 9:14 pm
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)

Re: Joe Gayo's lab tour

Posted: Mon Jul 01, 2019 6:22 am
by Lukas Springer
Your most recent graph shows some "oscillation" / quantized steps, any Idea as to where this comes from?

Re: Joe Gayo's lab tour

Posted: Mon Jul 01, 2019 3:23 pm
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.

Re: Joe Gayo's lab tour

Posted: Mon Jul 01, 2019 7:21 pm
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.

Re: Joe Gayo's lab tour

Posted: Mon Jul 01, 2019 8:22 pm
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?

Re: Joe Gayo's lab tour

Posted: Mon Jul 01, 2019 8:55 pm
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.

Re: Joe Gayo's lab tour

Posted: Mon Jul 01, 2019 9:07 pm
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)