Alexey's fusor progress

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Alexey Khrushchev
Posts: 106
Joined: Thu Jul 06, 2023 3:36 am
Real name: Alexey Khrushchev
Location: Moscow

Re: Alexey's fusor progress

Post by Alexey Khrushchev »

I finally got a new PEM cell delivered. It works very efficiently, with a voltage of 1.7V, current of 1A, deuterium yield of 8.3 ml/min. I purposely lowered the voltage to keep the gas from foaming the oil in the gasholder. However, there is an unpleasant moment, when the electrolyser is running, water rises up the hydrogen tube. I don't know where it comes from, I only pour water into the oxygen side of the cell. I had to make a drip trap to keep the water out of the desiccant cartridge.

Dennis mentioned that the bare contacts can cause corona problems. To avoid this I wrapped all the bare wires with duct tape and then covered them with a thick layer of plasticine. This proved to be a good insulator - breakdown is about 10kV/mm. And it seems to have worked, I stopped hearing the buzzing, I used to think it was coming from the transformer. Thanks again!

I also bought a leaded rubber apron to protect against x-ray radiation. It's old and heavy, about 4kg, equivalent lead thickness 0.3-0.4mm, blocks all the x-ray coming from the fusor. I just need to make a tinfoil hat and my wife will kick me out of the house))))
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Dennis P Brown
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Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Alexey's fusor progress

Post by Dennis P Brown »

Slate is a good shielding material - just use the density ratio to determine equivalent thickness require. It is cheap, safe, a non-conductor, easy to cut and drill. Just a suggestion.

As for the foil hat, well, just glad I wasn't drinking hot coffee when reading that part ;)
Alexey Khrushchev
Posts: 106
Joined: Thu Jul 06, 2023 3:36 am
Real name: Alexey Khrushchev
Location: Moscow

Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Last weekend my fusor produced its first neutrons! Working with deuterium plasma turned out to be more difficult than with air plasma. The pressure range in my chamber was from 8-12 microns. Even with hydrogen it was easier, I attribute this to the fact that hydrogen was not dry enough in my first experiments. Deuterium, on the other hand, I dried and purified from air residues very carefully. By the way, I have improved the cooling system, now the chamber does not get hotter than 40 degrees when running for 5 minutes at about 120 watts. I glued the waterblock to the fuser using TR-922 heat conductive glue. I did 7 experiments of 3-5 minutes each. The optimum pressure was 10 microns, voltage 25-30 kV, and current 2-4 mA. To measure the voltage I additionally connected an oscilloscope, according to it the real voltage was 10% higher than what my voltmeter showed. As a neutron detector I used a professional radiometer MKS-01R with a scintillation detection unit based on lithium-6 isotope, which is installed in the moderator unit and covered with cadmium from outside. It is an old device bought at a flea market, but I have tested its performance on an AmBe neutron source, but the detection efficiency is unknown to me. The radiometer allows you to measure the neutron flux per cm2 (fluence) for any measurement time. This greatly simplifies the calculation of the isotropic neutron yield. To do this, simply consider the area of a sphere with radius equal to the distance from the center of the fuser to the detector and subtract background neutrons. The background neutron count rate was 0.12 n/sec*cm2. Since I do not know the efficiency of the detector, I do not multiply the measurement result by a correction factor, so the actual yield may be slightly higher than I assume. In the table I give all the data measured during the experiments. The maximum isotropic neutron yield was recorded in the very first run and amounted to 9.3E4. In subsequent runs it was significantly lower (1.0-3.0E4), I do not know what this is due to, perhaps the heating of the chamber caused the release of gases from the rubber or vacuum grease. To test the radiometer, I changed the deuterium to air and ignited the plasma at the same voltage. At first the result disappointed me, as the radiometer was still registering neutrons. However, after 2 minutes the count rate dropped by a factor of 2, and further decreased until the 7th minute when the radiometer started to show only the background value. It seems that deuterium is well adsorbed by the chamber walls and is released for quite a long time even after air purging.
I made a short video showing the operation of my fusor https://youtu.be/VJyRAfCIhSI. You can see that there are often small discharges in the chamber, this does not allow me to increase the voltage above 30-35 kV. The breakdown seems to occur at the point of contact between the metal rod and the glass. In spite of some difficulties I am very glad that the fuser is finally working. Of course, the neutron yield is very low compared to most fusor builders, but for me it is already a great achievement. Based on this result, I can work further on improving the design.
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Dennis P Brown
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Re: Alexey's fusor progress

Post by Dennis P Brown »

Next step, record the performance with and without the moderator; that is the 'gold standard' for neutron proof. Especially for lower signals.
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Richard Hull
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Re: Alexey's fusor progress

Post by Richard Hull »

I agree with Dennis and have always preferred this method with any claim of fusion especially first pass efforts with unknown detectors and low per minute counts at lower voltages and currents.

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
Alexey Khrushchev
Posts: 106
Joined: Thu Jul 06, 2023 3:36 am
Real name: Alexey Khrushchev
Location: Moscow

Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Yes, I will definitely try to measure neutron flux without a moderator. I also want to do experiments on indium activation. The low neutron flux leaves little chance of success, but I will still try. As a moderator I want to use two 5 cm thick pieces of paraffin with an indium plate in between.
Alexey Khrushchev
Posts: 106
Joined: Thu Jul 06, 2023 3:36 am
Real name: Alexey Khrushchev
Location: Moscow

Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Looks like I managed to screw up my neutron counter..... Last time I leaned the detection unit against the fusor chamber and when I ignited the plasma there was a breakdown and the detector readings became meaningless. I rebooted it and it seems to be working, but now it's reacting to X-rays. I suspect that the pulse filtering system (I have a neutron scintillation detector) has stopped working. I doubt I can fix it. Now I will have to find an alternative way to measure neutron flux. I have a small B10 tube, but I don't know how to make it work.

In order to reduce the amount of arc breakdown at high voltage I replaced the 5mm steel tube with a 12mm rod. On one side I drilled a hole to hold the tungsten rings and on the other side I threaded M5 threads. I also formed the rod into a cone that tapers towards the rings. It was interesting to do this, but the idea didn't seem to work, the breakdowns at low pressure and voltages of about 40 kV remained. I think the discharge moves along the glass surface from the electrode to the chamber wall. I want to install a glass with a drilled bottom as a barrier, maybe that will improve the situation.
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