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: Questions answered
Date: Dec 24, 8:30 am
Poster: Richard Hull

On Dec 24, 8:30 am, Richard Hull wrote:

This is a bust out of that long thread........

Pierce Nichols asked is there any other way to get voltage into a fusor. He also asked about LN2 traps and vacuum in the 10e-6 torr range.


With the incredibly high price of vacuum rated insulators, making one's own looks real attractive.

This is pretty much what the Farnsworth team did when the voltages approached 100kv.

They used standard air insulators and packed them with either oil or parafin and beeswax. Placeing one of these on a flange is a chore in sealing and for vacuums in the 10e-3 range just a study in moderately good sealing. Most vacuum rated epoxies can suffice. For vacuums in the 10e-6 range, we are talking viton or indium or better seals which are very carefully done. I collect big HV insulators at hamfests and found a whopper on a chrome plated brass flange made for high power longwave Naval ship antenna feed throughs. It is of pure beryillia (th' best of th' best) and it cost me $10.00. I have tested it in air at 60kv and it holds as is. I will still fix it up a bit more and will probably have to arrange a flange on a flange hookup. The flange on the insulator is not vacuum rated.

The Farnsworth crew also placed either large aluminum balls (10") on the top and brought the HV cable inside of it, (distribute the E field) or they placed a huge pan of oil on top. We now have the silicone putty found at many electronic jobbers which i have used successfully to totally elimenate corona up to 50kv.

Inside the chamber, in a deep vacuum, the thing is to insulate only to a minor degree around the input conductor rod with alumina tubing. (Mcmaster-Carr).

A ceramic cup is often fashioned in the professional ceramic insulators about the central HV conductor within the vacuum area near the metallic shell. I made mine up out of TIG welding torch nozzle ceramics (few bucks at a welding supply store. True arc over in a vacuum is unlikely. The key point is watch what you put in the vacuum! Outgassing stuff is not allowed.

Vacuum-LN2 traps.

The micromaze is a good thing to have no matter what. It might even let you avoid the LN2 trap by not letting the more volitile mechanical pump oils into the diff pump!

In a good water cooled 2" diff pump, loaded with 100cc or so of Santovac or Pentavac fluids, coupled with a forced air or water cooled cheveron top baffle, an LN2 trap just isn't needed if 10e-6 torr is your goal.

For those experienced in micron vacuums, you will be in for a surprise as you drift into the higher vacuum regions. Cleanliness is everything. Bakeouts can become a must. Once 10e-6 torr is achieved, you will rather take a severe beating before you will want to take the system back up to air to change internals in the fusor.

Richard Hull