Anton’s fusor

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Anton Isaksen
Posts: 17
Joined: Tue Jun 01, 2021 5:53 pm
Real name: Anton Isaksen
Location: Norway

Re: Anton’s fusor

Post by Anton Isaksen »

A small progress update.

The greatest leak in the vacuum chamber, from the high voltage feedthrough, has now been fixed. The vacuum still isn't perfect, but I believe the remaining pressure increase comes from outgassing or water in the system. I tried testing this theory by letting the chamber sit 
at vacuum for an extended period of time. After one day, the pressure had increased from 50 mTorr to 900 mTorr, but three weeks later, the pressure had only increased to 4300 mTorr, meaning the pressure increase isn't linear. A bakeout will be attempted in the future.

Anyhow, I've experimented with turning the ring cathode 90 degrees around so that it's directed tangentially to the length of the chamber and not radially, meaning it's now pointed towards the walls 2cm away. This had the fascinating effect of increasing the fusion "sweetspot" from around 30 mTorr in the previous configuration to 112 mTorr. That's easily reachable with just the mechanical pump. However, I still pumped down the chamber with the diff pump for better gas purity. The following deuterium run at around 35 kV, 4 mA is one of my best runs till now, despite no prior conditioning, as shown by the data-graph below from my neutron detector.

Another problem is that the cathode tungsten carbide ring is held in place by a wrapping of tungsten wire around it, and as can be seen in the photo, the bottom part of this wire quickly heats up, increasing the risk of melting and wasting a lot of energy on x-rays. My chamber also gets very hot, so much so that a part of my camera melted due to it being too close (pictured below). For these reasons, I only keep the high voltage on for around a minute at a time, so that I can give the chamber some time to cool off. The next step is connecting the cathode ring to the HV feedthrough in a better way. Welding sounds the best.
Attachments
Counts graph.png
Cathode red hot.png
Damaged camera.jpg
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Dennis P Brown
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Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Anton’s fusor

Post by Dennis P Brown »

Sorry about the camera lens. Consider a 45 degree mirror for the camera to view the fusor cathode/window. That will eliminate the x-ray problem and reduce the heat load.

Also, could you give the detector's background count rate? You should get a few counts over a few minutes - not zero.

Why are you getting neutron pulses? A fusor should output a fairly continuous flux and the detector should show that (of course, there will be variation but not from zero for many seconds to suddenly 15 - 25 counts for a few seconds then zero and so on. That does not seem normal unless your voltage and/or current is all over the place as well.

My He-3 detector would give 500+ counts per minute minimum and the rate was continuous; fusor parameters: 30 ma, 22 kV and 5 microns pressure.

Your vacuum system certainly appears solid and that rate of increase is typical of out gassing.
Anton Isaksen
Posts: 17
Joined: Tue Jun 01, 2021 5:53 pm
Real name: Anton Isaksen
Location: Norway

Re: Anton’s fusor

Post by Anton Isaksen »

Regarding the detector, I have the cutoff voltage for neutron pulses set relatively high. This does lower the efficiency of the detector, but it’s mainly because I want to be sure that all of the electric noise from the detector is filtered out. I don’t have the most fancy electronics. Normal background is therefore around 1 cpm.

The reason for the pulsating neutron count is that I purposefully turn the voltage off to let the chamber and grid cool a bit, since parts of the cathode heat unevenly and I’m worried about it melting or the o-rings of the chamber getting to hot and outgassing. Its also hard to keep the pressure, voltage and current stable, but I’ll try once I’ve fixed the cathode ring. For now this seems to be the safest way of operating the fusor.
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