Deuterium run March 2015

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Greg Courville
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Deuterium run March 2015

Post by Greg Courville »

Things have been hectic the past several years. My fusor got left behind when I ran off to university, essentially fusion-ready but with instrumentation only half complete due to feature creep and a weird sense of priorities on my part. Several years later, I finally managed to put aside a weekend to come back and try a fusion run. I had about 48 hours to work with. All those months of designing electronics, building PCBs and writing C code back in high school, and it all got swept aside in favor of a LabJack, a scope and some hastily written Python code.

Somewhat embarrassingly, after this blitz of activity I was too exhausted and too busy (I had to immediately pack up and drive back down to So Cal for work) to go over the data, and it kept getting pushed further down my to-do list until it slipped my mind. Now I might finally be getting around to it.

To start, here's a quick video I threw together:
https://www.youtube.com/watch?v=CnJ236iyIDk
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Richard Hull
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Re: Deuterium run March 2015

Post by Richard Hull »

Looking very good! Hope to see that fusion report soon. It will be great to see a win after all this time, I bet.

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
Greg Courville
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Re: Deuterium run March 2015

Post by Greg Courville »

Thanks for the kind words, Richard.

A couple weeks from now I hope to have some time to go over everything that was recorded and give it a proper critical analysis. For the moment, all I have is a somewhat suggestive plot, which I have attached.

A full report will hopefully follow, but here are a few notes for now:
* Counting was accomplished by recording waveforms with an oscillosope. The recorded waveforms were hand-culled to remove obvious EMI/garbage triggers. This was done blindly, i.e. without looking at where each event occurred in time.
* The grid voltage measurement is going to be a little tricky to interpret, as my power supply is <s>half-wave-rectified</s> (edit: oops, actually center-tapped full-wave rectified) with an undersized filter cap.
* Deuterium injection was controlled by a pulsed solenoid valve and simple bang-bang control loop in software.
* I was not able to set up a discharge current measurement with what I had available, which is unfortunate.
* I didn't think to remove the BF3 tube from the moderator during the D2 run. I'm really kicking myself over this.
rough1.png
Last edited by Greg Courville on Sat Jan 30, 2016 4:09 pm, edited 1 time in total.
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Richard Hull
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Re: Deuterium run March 2015

Post by Richard Hull »

Thanks for the graphs. While well presented, the time scales are far too vast and the data is muddled. The pressures seem too high and the voltage too low. The time resolution is the big issue with the counts.

Fusors are typically brought to a relatively stable state of operation and counts are made over 600 seconds, constituting a "run". A run is a period over which the voltage, pressure and current are relatively stable, allowing stable counts to be made and perhaps a period of 200 seconds during which the BF3 tube is removed from the moderator to rule out noise and point firmly to whether genuine counts are there or not.

In short, it would be far more instructive, in my view, to get a stable operation point where counts are showing up, run for half the time, say 300 seconds with counts recorded and then just pull out the detector tube from the moderator for another 300 seconds.

If you are doing fusion, you are right on the noisey, low sigma edge of it with those pressures and voltages.

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
Greg Courville
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Re: Deuterium run March 2015

Post by Greg Courville »

Hi Richard,

I agree, it's not a very compelling dataset. I can re-bin the count plot (counts were recorded as individual timestamped events), but I'm still missing a real solid control to demonstrate genuine neutron production. The fact that I didn't have the presence of mind to just stick with D2 and try removing the moderator says something about the hazards of working under such an extreme time constraint. I think stepping back to think and plan for a bit could have resulted in a vastly better result. I guess using different gases seemed like a good idea at the time, but it made things more complicated than they needed to be and didn't actually work out that well.

I ended up borrowing back my deuterium supply and I'm working on a fixture to hold the detector in place with the moderator removed (the moderator was originally the main mechanical support for the tube mount and fairly heavy amplifier box). I have also changed the data acquisition setup slightly and will be periodically recording the actual waveform on the high voltage divider, which should give a little more insight into what is going on there. Knowing the output capacitance after the rectifier, this could also possibly be used to obtain a rough indication of the discharge current after-the-fact.
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