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, 09:16 am
Poster: Richard Hull

On Jul 05, 09:16 am, Richard Hull wrote:

>I'm close to ready to start turning my ideas into reality. I have some questions about sources of supply and construction of instrumentation.
>First: can someone recommend a solid beginner's book on vacuum practice? I have worked in a physics lab on vacuum stuff, and did attempt to learn as much as possible, but it would be nice to have a complete reference.

This is a real toughy....

The very basics of vacuum can be had for free in the tremendously valuable Kurt Lesker catalog complete with tables, formulae, etc. However, the "Bell Jar" is a quarterly publication for amateur vacuum enthusiasts and is often choke full of good tips in practical amateur vacuum stuff. A search on line will let you print volumes of stuff out regarding vacuum basics.

My favorite vacuum books are those which are part of the AVS (American Vacuum Society) classics series! The are old, they are good and written long before the need to confuse the reader arose.

The following are my choices amoung the AVS series

Vacuum Technology and Space Simulation
David Holkeboer, Donald Jones, Frank Pagano, Donald Santeler.

Vacuum Sealing Techniques
A. Roth

Handbook of Electron Tube and Vacuum Techniques
Fred Rosebury

These can be had from the AVS (on line) or Verlag. They can probably be ordered at any good book store in your town. They are paperback and about $39-$50 each!!!

Another excellent book is "Vacuum Tubes." by Spangenburg, part of the famous McGraw-Hill Electrical and Electronic Engineering Series. It is long out of print.... I got mine on line used book searches (about $40.00)

Richard Hull

>Second: has anyone built a HV Langmuir probe, and how? Since I plan to go with a magnetized grid EXL machine, it's crucial that I be able to measure the voltage of the inner electron cloud in real time.


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.

Richard Hull
>Third: how can I build my own HV feedthroughs? They are very expensive, and I'd like to build my own if they are not too difficult to build.


They are indeed tough to build. The need is for a low outgas material of superior dielectric strength, superb mechanical properies, coupled with high temperature attributes. Plastics, Are lousey mainly in the outgas and temperature region. Teflon is about the best, but it will need to be constantly re-tightened in the mount as it cold flows badly. I used this arrangement on fusor I and II where neutron production was not a major goal

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.

Richard Hull
>Fourth: can anyone suggest good sources for high-voltage, high-vacuum varnish?

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.

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. 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.

Richard Hull
>Fifth: this is directed at Rich Hull -- what is the contact info for the place you had spin your hemispheres?


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.

Richard Hull