Is It A Farnsworth... or a Hirsch (redux)

[Dennis P Brown]

First off, fantastic over views (many!) on the history of how fusors (any) developed. Such detailed work by Richard and well supported down to Rutherford's original efforts in nuclear research adds both depth and direction; and so much of his post is based on direct interviews from many of the fusor principles! That is how professional history is really written.

Next, from the various discussion's in Richard's posts I see that the first attempts by Phil were based on the plasma approch - classic 1950's work first started by various government groups in the early years - but Farnsworth's group used glass(!) housings for their first attempts. Many a demo has followed that path!

While certainly Phil Farnsworth is the direct inventor* of the fusor concept we tend to use, the reading indicates the most successful first device - not first nor successful as a energy device as in significant fusion but significant fusion relative to what was thought possible at the time(?) - was the "Multipactor" (?)

In any case, I assume that the "multipactor" that got their attention - via some nice neutron numbers(?) - and that device's component's certainly looks to be - basically - the fusor we here tend to copy except we tend to use metal, rather than outer glass envelope they used. That is, it appears to have a cathode (center wire) and metal outer anode (metal coating inside the glass) system and I assume D2 gas inside at a low pressure.

So, one point I am still fuzzy about is whether the "Multipactor" is a Hirsch-Meeks (HMV) design and as such, a variation/evolution on the original "AFF"? Or was that the Multipactor the inspiration for later efforts by Hirsch and Meeks?

This ridiculously short summary (incorrect?) here is what I gather from reading the various post's by Richard.

Paul being the person that was also involved in summing up some of the work on this thread, as well has certainly adding details/summaries here is why I decided to post this on his thread rather than Howard's intro or Richard's.


*Whether Phil designed the later fusors or not is really irrelevant - this entire effort was his original concept, first major efforts and that is what matters

[Richard Hull]

Again, the multipactor is a very old device. It never did fusion. Farnsworth invented this and vacuum tubes were made up and sold as multipactors. I can't say much for their use. Farnsworth noted that with a high enough frequency of oscillation on the two half spherical electrodes he could create an electron "knot" in the center of the device in the image. The grid would supply the electrons as it was a heated filament! (two wires out of the base). A negative potential well would form in the center with the right frequency bunching up the electrons.

The original fusor patent shows an RF input to his fusor. To my knowledge and from what I got from the techs, at no time was there ever a high frequency source of power hooked to any fusor!!!!! That's right! In the early days 59-60 Farnsworth was directly involved with his fusor concept and construction. Did he find that he could not multipact with all the other electrodes in the device?

The multipactor tube, as seen, is a high vacuum device and can easily create the negative well at a given frequency. The fusor has gas in it and a plasma of both ions and electrons. I am sure this destroyed the negative well concept of the multipactor in the fusor. The multipactor has only electrons in a high vacuum.

Again, did they see this hopeless situation and never used the RF source in the patent? Your guess is as good as mine. In a plasma, separating positive ions from electrons is like trying to herd cats.

Richard Hull