Bubble Detector Result

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Dennis P Brown
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Bubble Detector Result

Post by Dennis P Brown » Sun Dec 24, 2017 4:28 pm

Tried a Bubble Detector after deciding I wanted to get a definitive test on the neutrons production using the smaller anode volume. The Bubble Detector is rated: 22 bubbles/2.1 mrem.

Of course, this is a somewhat insensitive detector compared to many posting here but it is nice to get confirmation via another methodology after having issues with my previously working BF3 tube detector system. I'll have to do the calculation later when I have time since have a lot of things to finish today (lol.) Just couldn't hold off on posting the results.

Later after the holiday, hope to have time to measure the output without the reduced anode volume. Also, at some point, want to try my 40 kV (5 ma) supply instead of this 31 kV (can can support 40 ma for twenty minutes since the x-former is now air cooled.)
Attachments
MVC-031L.JPG
Bubble Detector with Bubbles (3 Bubbles in 15 min.)
MVC-029L.JPG
Voltage and Current in Fusor (Pressure: 14 microns)
MVC-030L.JPG
Bubble Detector Location on Fusor (Cathode visible)

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Richard Hull
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Re: Bubble Detector Result

Post by Richard Hull » Sun Dec 24, 2017 6:44 pm

Good going on the bubble detector. I always bought a 33 bubble/mr detector. 31kv@35ma is a real grid burner power level. You must have heavy wire in your grid or don't run very long. I really avoid currents much over 15ma once I hit 35kv or more on my tungsten grid.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Dennis P Brown
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Re: Bubble Detector Result

Post by Dennis P Brown » Mon Dec 25, 2017 11:36 am

Yes, I use a very heavy continuous (un-welded) gird and as I mentioned in another thread, this unit can handle 30 - 40 ma @ 31 kV for at least 30 minutes; the forced air cooled electrode and water cooled fusor chamber does enable one to handle those rather high power levels without grid melt down or gas feed line failure (almost had that happen in my first fusor runs a year ago. Also, I added forced air cooling for the x-former, too.) Since my DP is water cooled, adding a water stage to the chamber was, literally, trivial (the wonders of good AP Weld epoxy and copper tubing.)

Apparently, some here have posted with more sensitive bubble detectors; I did note that this bubble detector (per its paper work) is very sensitive to low temps (i.e I tried using it at around 14 C and didn't really respond - at all.) They indicate its lowest working temp is 20 C and once I reach that temp only then did I start to see data but that might still be lower than optimal.

Also, I see your bubble detector is 3.1 times more sensitive than mine. Well, mine was purchased second hand so I didn't really have any choice in its sensitivity level (newbie's who decide to buy these devices might want to take note and get as sensitive bubble detector as possible) but that difference is good to know. Still, it works fine for its purpose (my fusor does produce enough neutrons to get a significant signal) and with some effort (warmer room temps, maybe ... lol) I can use it to get back to work on building my other detector systems by using it to better calibrate my chamber.
Last edited by Dennis P Brown on Mon Dec 25, 2017 4:15 pm, edited 1 time in total.

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Dennis P Brown
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Re: Bubble Detector Result

Post by Dennis P Brown » Mon Dec 25, 2017 3:52 pm

Happy holidays one and all celebrating today.

After exchanging gifts with my daughter and girlfriend, I decided I had time to run a quick fusor experiment to see if my orginal idea about fusor chamber size (really anode/cathode separation/volume) was a significant effect.

I removed my "smaller" anode assembly I used in the previous experiment (see above) and ran my fusor with its regular (larger) anode. The results were interesting and followed the logic that has been suspected using smaller chambers - that these might lead to higher neutron counts.

Following this logic and keeping all else constant, I reconfigured my fusor to have two very different sized anodes. Yesterday, I reported that I obtained three bubbles on my detector in fifteen minutes of operation ( Power: 31/32 kV & about 40 ma; detector: 22 bubbles/2.1 mrem.)

Today, I removed the small anode and used my full chamber (walls) as the anode. My operating pressure decreased from 15 microns to 8.5 microns. With a run of fifteen minutes and about 40 ma, I obtained 1.5 bubbles (really.) Turns out I had a very small bubble just starting to enlarge after the full one had appeared (but significantly larger than the normal tiny bubbles in all the detectors.) See first picture.

I ran the fusor for five more minutes and that bubble certainly started to grow to full size - see second picture.

From these two runs I do believe that these experiments provide strong evidence that smaller chambers with their higher pressures do, in fact, lead to greater neutron flux rates for identical voltages/currents using identical chambers (except for the smaller anode added for the first posted results.) Of course, while more runs will further provide better data, considering the results previously posted for small chambers, I just wanted to provide an experiment where the only variable was anode/cathode separation/volume.

These results are consistent with the fact that fusors achieve fusion solely via tunneling; any fusor constructed such that its operating pressure is increased (but its power is unchanged) will increase its neutron flux rate in a somewhat linear fashion since tunneling probability is increased and for fixed kinetic energy of ions (KE was held constant in my experiment so is irrelevant here. Of course higher voltage in a fusor will increase fusion rate since one is reducing the Coulomb barrier making tunneling slightly more probable. In my runs, KE is held constant so this isn't a factor for my experiment.)

So, in conclusion, bigger is not better for a fusor chamber. A fusor with a smaller chamber will provide a larger neutron flux for the same power level compared to a larger chamber using that same power (identical current and voltage levels.) Of course, pressure is increased but not necessarily more gas; in fact, one can use less gas compared to the larger chamber volumes - see the fact my chamber in both experiments was the same - only the anode size change that resulted in higher deuterium pressure/density was the only variable changed.

As such, I believe these experiments do indicate that people deciding to build a chamber should consider smaller chambers if their primary goal is to achieve detectable fusion rather than have room for new cathodes designs or space for special detectors or needing volume to add other special devices in the chamber.

Aside: someone with a more sensitive bubble detector or calibrated BF3 or He-3 detector system should consider a similar experiment.
Attachments
MVC-033L.JPG
Single fully formed bubble (fifteen minutes fusor operation; just to the right of near center) and second one just forming far to the left near the center line
MVC-034L.JPG
Two bubbles (20/21 minutes fusor operation; the tiny original bubble is now larger (is well to the right of the first bubble - near the end point of the detector tube )

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Richard Hull
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Re: Bubble Detector Result

Post by Richard Hull » Mon Dec 25, 2017 6:06 pm

I figured that you acquired a second hand bubble dosimeter. When buying new you can, and should demand, the more sensitive binned dosimeter.
Good work and reporting.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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