A "lightsaber" feedthrough

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Pablo Llaguno
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Real name: Pablo Llaguno

A "lightsaber" feedthrough

Post by Pablo Llaguno » Sat Mar 14, 2020 7:13 pm

Many have been recently building smaller chambers, their own feedthroughs, cheaper neutron detectors, D2 from PEM cells, etc., to help in keeping costs down to the fusor builder. Here is my take on how to make a cheap feedthrough that can take more than 50kV, it also looks like a lightsaber.

It consists of a spark plug, ceramic tubes, pvc pipe, hysol epoxy and a lot of epoxy resin. I used a cf 2.75" as my flange for the feedthrough and tapped a 14mm thread for a Champion 220 spark plug (I really recommend this type as it has a long conductor and is of the non resistor type). I applied hysol on the sparkplug threads to mantain a vacuum seal. Then I milled a recess for the PVC pipe on the outside of the feedthrough.

On the inside I used an alumina tubing and a broken ballast for the larger ceramic tube. I used 12 gauge copper wire to make the electrode of the feedthrough longer. All electrical connections on the vacuum side of the feedthrough were done with crimp tubes. I applied a lot of hysol around the electrode of the spark plug as this is a weak spot for electrical breakdown and hysol has high dielectric strength.
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Here you can see the arrangement
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On the non vacuum side, glue a cap and a terminal to the pvc pipe. Connect the terminal to the sparkplug. Fill the thing with oil/resin or whatever material you have that has a good dialectric strength and won't damage the pipe/ceramic/terminal.
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Workers at the workshop were asking me if I was building a lightsaber
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I tested the thing with a 50kV dielectric strength tester (in Mexico we call it a hipot) and there was zero, nada, current flowing through ground and the electrode. Hopefully this will allow to me fuse some deuterium, it has already achieved plasma on my fusor.
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Richard Hull
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Re: A "lightsaber" feedthrough

Post by Richard Hull » Sat Mar 14, 2020 9:27 pm

This is a fine idea except for the hysol linking the pipe to the flange. Expansion and contraction are an issue, long term. A real fusing fusor will heat to a very high temperature. This includes the insulator feed-through flange. I am sure we will all be interested to see how this holds up once some serious, lengthy fusion is taking place. You could actually test this out without deuterium, just leak in air to about 10 microns and run the fusor up to about 20kv and 10 ma for a while until it is very hot. Let it cool and then try again. See if the system remains vacuum tight over several hot then cooling runs.

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.

Pablo Llaguno
Posts: 98
Joined: Sun Feb 05, 2017 11:00 pm
Real name: Pablo Llaguno

Re: A "lightsaber" feedthrough

Post by Pablo Llaguno » Sun Mar 15, 2020 12:40 am

Will test accordingly when I fix my supply (or get a new one). Perhaps there is a better material to join the pipe to the flange than epoxy, however it must be non conductive so as to not short the main electrode with the flange. This is just one take on how to make a feedthrough, there's also Liam David's excellent and way better looking feedthrough. I guess one could try milling his own flange adapter for a quartz tube and seal it with swagelock fittings.

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Maciek Szymanski
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Re: A "lightsaber" feedthrough

Post by Maciek Szymanski » Sun Mar 15, 2020 11:55 am

I’ve very good experience with the picein as the sealing agent. I’ve lately used the Edwards Wax W for making HV feed through for the thomson parabola spectrometer I was building at work. The feed through is made from the standard C50 concentric connector sealed (similar to BNC but bigger) with the picein wax from vacuum side. The system pumps down to 2,5e-6 hPa and holds 4 kV (maximum voltage from deflection plate supply).
The picein is easy to work and dismantle and temperature resistant to about 80ºC.

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Complete chamber with MCP. The C50 connector is on top plate next to the bing flange.
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Picein sealing on the vacuum side of the connector.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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