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: W wire
Poster: Richard Hull

On , Richard Hull wrote:

>I can provide quantites of Tungsten wire for research purposes, such as fusor grid construction.

Iam sure some of the more serious experimenters here will take you up on that offer.

>As for Tantalum wire for the grid, I would expect that it would embrittle rapidly because it is a good getter, especially in a Hydrogen atmosphere.
>But then again, I hear they use Ta sheet in ion sources.

I have used Tantalum extensively for grids and other items in vacuum environments. It is a good getter and embrittles terribly. As there is zero physical trauma involved in fusor operation, embrittlement is a non-issue. Actually I have found it to be a plus! the grid is made by closing Ta loops to circles. For those silver soldering, the fear is that the grid will heat and the loops will pop open once the silver solder softens. With massive imbrittlement, the wire quickly becomes absolutely rigid and inflexible. The loops are held closed now by memory via embrittlement and the entire grid geodesic is held together by surface tension of the softened or even molten silver at the joints. This assumes total mechanical stability of the fusor mounting platform. (no vibration from pumps, etc.)

Tantalum will spot weld (resistance weld) well. Tungsten will not do as well. The secret to any good grid construction (as I have recently found out) is to use ultra fine SS wire to bind up the cross points in the geodesic and then fill with silver solder. This gives a superior mechanical connection and wicks in extra silver solder. The art is to heat gently and minimize and the bulge at this point. (this is for those with no resistance welding capabilities.)

Richard Hull