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: Fusor Operation - a general question
Date: Jul 04, 7:38 am
Poster: John

On Jul 04, 7:38 am, John wrote:

>Been thinking about the operating problems recently discussed here....grid losses and gas collisions, to name just two, and it occurs to me that perhaps....the fusor is best operated on a "once through" ion collision basis.. rather than on a recirculating ion basis.
This would be nice, but the nature of the ion and its coulomb forces do not allow this level of ballistic precision. While it has not been confirmed beyond a reasonable doubt, many IEC researchers agree that most of the fusion reactions in the fusion zone are not head on collisions but side collisions, thus the correlation between the higher voltage and higher reaction rates.
>The experts here, please feel free to jump in and correct my misunderstandings. It seems that one of the main strategies of Farnsworth's Fusor is the recirculation of ions to create "virtual" anode and cathode structures (otherwise known as concentrations of ions), the latter of which is where the fusion occurs.
I think its important that we all understand what a virtual electrode is. I'll skip the basic formation of the virtual structure, because I think we are all familiar with that sequence of events. In a fusor like the kind we make, a large majority of the electrons are lost to the grounded spherical vacuum chamber, in this case an anode. The electrons that form the virtual cathode are those that remain inside the cathode grid in a state of dynamic ballistic motion, in an out of the reaction zone. It's when these particles come to there U-turn points (do to electrical attraction and repulsion) that for that split second the particle charge forms a space charge that acts a virtual electrode.
>But... the grids needed to establish these spherical potential shells actually become an energy sink, since they are not and cannot be 100% transparent.
The inner cathode grid in a fusor is a steady unbending structure that sets in motion the chain of events that lead to virtual cathodes, without it many have found it impossible to generate the virtual electrodes that fusor's depend on for there continued reactions.
>However, if the ion guns are built to produce very well focussed beams and aligned to illuminate a small central reaction zone, then the non reacting ions will simply exit from this zone, and decelerate toward the outer grounded fusor shell.

The reacting ions will produce the neutrons and contribute to additional kinetic energy of the surrounding gas ions.

By setting the ion guns radially inward from the ground shell and operating them at a modest negative bias from ground, the unreacted D+ ions upon returning to the outer shell region become neutralized by collision with either Fusor walls or a ground potential electrode screen, at quite low velocities (and therefore nearly zero energy). They can be gathered up (i.e.: pumped) for reinjection at the nearest ion gun.
The most serious problem here is that there is no source of electrons and therefore you have just ions. The problem is that I think the dominant force in this scheme will be Earnshaw's theorem, because both the reaction zone and the outer wall will be positive or in other words potential hills for the ions to overcome.
Add to this the fact that you need reaction rates above 10^12 just to get 1watt of energy out put and you have a serious problem.
>Electron guns for SEMs can produce nm size spots, indeed the useful spot diameter is usually partly limited by the enerergy the surface can absorb without deformation. Ion guns should be capable of similar focus.

May be this is what is normally done... and I just missed the point. Comments please.

Dave Cooper