Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: various instrumentation and parts questions
Date: Jul 05, 4:58 pm
Poster: Pierce Nichols

On Jul 05, 4:58 pm, Pierce Nichols wrote:

>A spherical device like this can't be effectively probed with the classic langmuir probe. (many have tried) It upsets the field far too much and the results would be way off base. If you think about it, you can see why.

I can see it, b/c of the grounded shield. Has anyone managed to build a probe for this purpose?

>The classic porcelin/metal seal is the best thing going. I trust you read my extensive posting here on the use of the superb spark plug #44?! Check the back listing. I am using this arrangement in fusor III. I have since picked up, in trades and hamfest buys, a couple of professional vacuum SS weld type insulators which will be used on Fusor IV.

I have. How much voltage can those things take? Are things like truck plugs etc rated for higher voltages? I take it you just weld them into a flange and away you go, or is there something more? I also want to figure out how to make coax feedthroughs for instrumentation.

>Regular Shellac works OK, but there are some superb "glops" that outgas no worse than 10-6 torr which are specially formulated to dry and yet remain flexible or rubbery.

Names? I have access to an electric kiln, so I can temperature cure if necessary.

>There are special RTV's, Epoxys and sealants.
>I have used "Inland Seal" a lot (from Inland vacuum), but you need to let it cure for about 4 days.

Does it heat cure?

> A trip to the Duniway and Lesker catalogs will yeild up a bunch of then. Note* they are all rather expensive due to their special nature. The best vac grease I have ever used is one of the Apiezon greases 25 grams for $100.00.

When I worked in a plasma physics lab I used that stuff. I don't plan on using it for my project -- copper gaskets are cheaper! I also expect the chamber to heat to close to the max rating for O-ring seals from particle bombardment. I have a line on a 37 kW xray machine that I can have for the price of shipping, or maybe a few hundred dollars. I also have a line on a couple of Army surplus towed gensets as well that I can borrow.

>I may have posted this before..
>Maryland Metal Spining
>contact Chuck Mitchell
>1 (410) 466-6400
>Example pricing 6" hemispheres in 304-308 SS were about $65.00 each hemisphere in 1997 and the recent 10" hemispheres I had made were about $110 each. This is heavy metal too .060". I think they deep dish form these jobs and do not spin them. They can do this work up to about 24-36" diameter, as they have many standard diameter dies on hand. Ask for a 7.4036" diameter and be ready for a $1000 die charge.

How did you rig the flanges? I've priced real flanges from Leskers etc and the prices are absolutely prohibitive. I was thinking of buying SS or aluminum flanges for some other application and having a gasket groove put in on a lathe. I have access to a TIG rig and someone who knows how to run it, so the welding won't be a problem.

Thank you for taking the time and energy to answer my questions; you have been extremely helpful.

Pierce Nichols