Fusor polarity

Reflections on fusion history, current events, and predictions for the 'fusion powered future.
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Maciek Szymanski
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Fusor polarity

Post by Maciek Szymanski »

I'm still putting together the material for my seminar, and I've started wondering what the "polarity reverse" of the ITT fusor in 1962 exactly was? They had an electron injection, positive grid system. While changing grid polarity is trivial, changing electron guns into ion sources is rather impossible. Thus I wonder what really this first ITT fusing machine was? Do they simply postponed the guns and made the simple direct ionization fusor? Or the electrons were still injected to assist the ionization in the way that the hot filament was later used in the famous AEC demo system?
And the second thought. Why the electron injecting machines did not worked? The Elmore Tuck and Watson article shows, that this configuration in theory should work. The possibility of reaching break even required plasma densities was questioned due to stability problems but it may be expected that this configuration should produce detectable amount of fusion. As far as I know nobody has tried this configuration until Bussard. And Bussard's results were also rather miserable, but still I was not able to find any theoretical (or experimental) analysis why this configuration is inferior.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
Frank Sanns
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Re: Fusor polarity

Post by Frank Sanns »

Back more than a decade ago, I wondered such things and built my Levitated Pit Fusor. Well, I built it to answer a few questions but one was polarity.

Changing polarity between two leads, even if one is ground, is easy and it works. Potential is relative. Charge however is not relative. Charge is absolute.

With spherical chambers and grids, charge wants to be on the outside of the grid and not on the inside. The results of my experiments show that a negative inner grid and a positive or grounded outer grid (well away from the chamber walls), is not the same as the reverse. That is, you can attract ions to the center of the inner grid (chamber) with a potential, but you cannot "push" them there with a repulsive outside potential. Again this is because charges move to the outside of a conductive sphere to minimize energy.

Here is a link to my work.

viewtopic.php?f=18&t=7807
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Richard Hull
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Re: Fusor polarity

Post by Richard Hull »

There were no ion guns on any of the first basement and early upstairs lab fusors. As such, the reversal occurred by just grounding all the electron emitters, (no filament power), field emission produced the early electrons to make local ions and as noted the grid was made negative hot. This work was done rather late after waisting a couple of years before getting the PNC-1 neutron counter. When Farnsowrth's way of getting fusion produced no neutrons, (in spite of Farnworth's claims that he was doing fusion), the team was upstairs at this time in the big lab and did succeed in doing a little bit of D-D fusion once reversal took place. From this point the next few fusion systems were designed with ion production at the shell of the system being accelerated to the negative central grid.

To your second question.......The electron emitters with the positive grid demanded the RF generator to cause the multipacting electron knot within the grid. They called this giant grid a "dynode". As I have admitted to Paul Schatzkin on two or more occasions, I do not think that the Farnsowrth's idea was ever really tested in a true neutron counting environment!!! It was two years into the effort with Farnsowrth's true system operating with no neutron detector present!! Pressed for results, when a first pass with a neutron counter was made, there was no impetus to seek a reason why the Farsorth system was not doing detectable fusion. A reversal was made and it worked! Farnsworth was out of the day to day oversight and having seen a simple reversal work first time, the team never looked back or studied Farnsworth's idea in a manner that might have made it work. Instead, buoyed by positive results that pleased ITT, the reversal idea was the path forward for them at that time.

Ion guns were the order of the day, made up by Gene Meeks and spurred on by Hirsch, the result quickly exploded into fusion numbers that were just getting beter and better.

Sadly, I regret that I never asked anyone on the team that, in hindsight, if anyone of them felt like Farnsowrth's original idea might have worked if they had revisited it once they were on firm ground regarding neutron detection. They are gone now so that point is moot.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Maciek Szymanski
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Re: Fusor polarity

Post by Maciek Szymanski »

Thank you. That's what I expected. It is something that fascinates me in the progress. Many times a new idea that leads to immediate results causes that the other branch of research is abandoned. I'm always wondering "what if?". Like "what would happened if transistor would not caused vacuum tube progress to stop?". Sometimes progress even makes a large arch and reinvents the wheel - like going form mainframes and terminals through personal computers to the web based servers and clients and cloud services (so again back at the mainframe and terminal model).

Frank! I think that the main difference between the negative and positive design is the particle mass. Electrons and ions have completely different inertia, and inertia is a key concept in IEC. I would risk to say, that negative grid system is the only one going to work with direct glow discharge ionization. The high vacuum, virtual cathode design may work - for me that is still an open question.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
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