Spark Plug Feed-Through Concept

[Brian_Gage]

Though I have often heard about using a spark plug as a feed-through, this may be a novel twist.
On Geiger Counter Enthusiasts, a member suggested, 'who says the spark plug has to be used in the normal way?'. Peter's idea was relating to construction of a pressurized ionization/GM chamber. Screw in the spark plug from the inside. Use the screw-off cap and threaded end to connect to the anode. Clip or weld a lead to the tungsten spark gap end on the outside.

As soon as I read this, I thought of Frank's "pillar of fire" cathode in a fusor. Considering two hemispheres of a fusor chamber, just make it to size so that when two spark plugs are screwed into the inside of the hemispheres (ceramic insulators inside instead of outside), their screw on caps or threaded top ends are the appropriate distance apart. You then have a spark gap negative center grid to attract the D ions.

Please pardon me if somebody else has already posted this idea. I had been considering using spark plugs as feed-throughs for my first demo fusor. Reading the GCE post caught my fancy.
Best Regards

[Chris Bradley]

Brian,

You might like to read my post and my notes on how I have done this;

viewtopic.php?f=11&t=4893#p27731

The picture shown how I have installed not one, but 8 spark plugs for feedthroughs with the 'electrical' end of the plugs in the chamber and the 'sparky' end outside it.

It works brilliantly for my application, but the thing to note is this; the thread does not appear to seal well to vacuum, you can't rely on that. So you're left with using a seal where the fire-ring goes.

But in a regular discharge device you might see some effects around where the seal is. I guess there are mitigations you could use to protect it ... or try the fire-ring?

Now, it may be that the regular compressible fire-ring that comes with the plug could do a vacuum job. I can't say, and I'd certainly not try with my aluminum bulkheads as the fire ring will likely damage the bulk-head surface. Instead I used a nitrile ring. This needs to be, pretty much, as small as you can reasonably stretch (not over stretch) over the thread so that as you clamp the ring it resists squidging out. Also, find one not too thin so that there is a decent contact area with the surfaces to seal.

[Brian_Gage]

Hi Chris,
Thanks for the info. Needless to say, I miss a lot when sifting through these forums. I've posted your link on GCE for the guys who were discussing using a spark plug in the construction of a gas pressurized ion chamber/detector.
Eight spark plugs making an inverted hedge-hog! Must look interesting.
Thanks for the feedback.

PS. I tried sending this message to you direct using your e-mail link here, but that resulted in my getting an "undeliverable" e-mail reply.

[Chris Bradley]

I was just trying to cut down the email spamming junk (our emails are easy to haul off this website) - The email address I put in should be readily understood to a non-robot, but understand the issue in your case. Will drop you an email, feel free to contact me ..

[Richard Hull]

I assume the spark plug is related to fusor operation? I started the spark plug bit back in 1997, but found it to fail if you are looking at real fusion over the long haul.

I never tried to push the plug beyond its normal breakdown point for me at about 20-25kv applied, no matter how I configured it. It is superb for a demo fusor at most any level, though.

My first fusion was done with a larger cobbled up insulator from an old blown 30kv capacitor. Fusor III had a formal, but cobbled up HV insulator machined into and mounted on a 2.75" conflat flange. Fusor IV is using a really nice, formal beryllium oxide U.S. navy antenna feed through insulator, also mounted in a conflat flange. With some care, electrostatic shielding and only 2 external flashovers in the past, I can nurse it to ~45kv in air. It has never faulted internally.

Richard Hull