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: Circulation
Date: Nov 02, 08:55 am
Poster: Richard Hull

On Nov 02, 08:55 am, Richard Hull wrote:

>Has anyone ever thought of reducing the background gas pressure to increase circulation and therefore reaction rates while the a fusor is in operations?

Yes! It has been done. A lot of things seem like it would be ideal. The mean free path grows meaning larger chambers can be used. The circulation increases meaning more of the stuff arriving in the poissor at full energy, etc. However, there are less stuff arriving as the reactants in the chamber are diminished (you pumped 'em out, remember?)...(fewer D2 atoms).

There is a trade off. Below 10-4 torr (.1 micron), the nice ionizing glow discharge goes out forever and either ion guns or dispenser cathodes are demanded. Stainless chambers are a must and either a turbo pump or well kept diffusion pump is required. The simple amateur, inexpensive, fusor is no more. RH

>I know this has been brought up once before, but why can't someone make a simple ion gun to pre-ionize the fuel and inject it with minimum neutrals?


They can, but amateurs are not in this for the long haul! Ion guns mean vacuums in the 10-5 torr range or either differential pumping. Few amateurs are willing to stumble into this area.

There are many classes of amateurs and observers on this list. I have found two distinct classes.
One group, the builders often make a demo fusor and get the nice glow and maybe even a hint of a star. This often satisfies, and they move on to other things. Others use it as a learning experience and take a breather planning for stage two. Since they are doers, they need constant action and advance and often don't plan impovements well. Their execution is often not very satifying to the eye, but always seems to do something close to "as planned" (I am in this class).

The second group are the theoreticians, thinkers and folks who really don't want to plow any money into anything unless it is born whole-formed and a stunning success at the extreme end of the endeavor. This warrants they will never actually have to do anything. The job just gets too staggering and calculated costs soar as they mock plan the effort. Most in this class just give it up at some point.

This is no slam against either group it is just a cold statement of the realities of human nature. Both assist in the effort as the theorists musings throw ideas into the head of the doers and the whole effort is nudged along. RH


>I mean it's not like you are trying to drive the reactions with it, just decrease neutrals and inject the fuel in a precondition state.
>Hell, if we are making fusors I think a simple pre-ionizer should be no more difficult.
>Actually, I was thinking, if you make the smallest possible grid that can still do the job and will last just long enough, you could reduce strikes against the grid and increase circulation further and if for just a few minutes, you might just get to higher reaction rates.
>Just some ideas.


This is the very idea in the Hirsh-Meeks patent!
Throw in a simple dispenser cathode, keep the electrons serpentining about the ionizer grid near the outer wall and let nature and electrostatics do the rest.

They had farted around with enough ion guns over many years, differentially pumped, etc, but their best machine was a simple idea with rather high gas pressure. The last "cave" machine of Bob Hirsch's did use ion guns and was the center piece for the BYU's fusor effort under Andrew Gardner with Meeks as an assistant until 1972-73 time frame.

Ion guns work great, but are trickiy to have function well and a minimum of four are needed according to the original team. Amateurs are pretty much aced out of this arena.

Richard Hull