Mind twisting riddles of fusor operation

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Maciek Szymanski
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Mind twisting riddles of fusor operation

Post by Maciek Szymanski » Tue Dec 10, 2019 9:58 pm

I've spent last two weeks digging through the forum archives and reading books and articles on gas discharges, ionization, mean free paths, cross sections and electric fields and trying to put together what is really happening inside a fusor. The more I know, the more complicated it becomes. It's really amazing that such a simple device can have such complexity inside.

I've found following threads very interesting:

FAQ - Fusor - detailed theory of operation

#7 FAQ- mean free path

Nevertheless I've some thoughts and ideas I would like to share and discuss.

The mean free path of deuteron at typical fusor pressure of 0,03torr (0,04hPa) is in order of 10cm (about 4") so it is comparable with the diameter of the chamber. For electrons it's about 5 times more. It means that most of the electrons will pass through the space between the cathode and the anode without any collision (so it will not ionize any dueter molecule). It is consistent with the glow discharge data - extrapolating form Steenbeck measurements the length of the cathode dark space for hydrogen and iron cathode at 0,03torr will be 30cm so self sustained glow discharge at this pressure is not possible (typical glow discharges are down to 1torr, so we are operating two orders of magnitude lower).

For other hand for my fusor with grid wire diameter of 0,4mm and grid shell distance of 33mm the maximum electric field at 20kV can be estimated as 10E5-10E6 V/cm. This is quite strong field. It's one order to weak for significant cold electron emission, but should be enough for some tunnel ionization of deuterium molecules. I'm still searching for some good papers on tunnel ionization and for the moment I've no means of estimating ionization rate. As the fusor is filled with deuterium molecules (D2) not atoms most of the formed ions would be dideuterium cations not deuterons. And most of those ions will be lost either hitting the grid (they are formed just around the grid in the strong electric field) or will immediately recombine with slow electrons. The trace of this process is faint glow around the grid wires, where recombined neutral atoms return to the ground state. The electrons which have not recombined with the ions around the grid are quickly accelerated towards the anode (fusor shell).

The maximum cross section for impact ionization of deuterium by electrons is at about 70eV. With -20kV at the cathode and taking in account very long mean free path of electrons at fusor operating pressures it's almost impossible for this kind of ionization to happen. The collision must occur in the very narrow band between anode and cathode, where electrons have just right energy to ionize. So it seems that 100% electrons hits the anode. But those electrons generate quite nice stream of X-rays focused towards the center of the fusor. And X-rays do ionize and dissociate deuterium into deuterons in the whole volume of the chamber. Quite much of them has chance to be accelerated to the fusion energies.

And there is another process happening on the grid. The "lost" ions created by strong field heat the grid up and the thermionic electron emission begins, leading to increased X-ray production, thus increased fusion rate.

So summing up, my model is:

- Almost all ion current is due to tunnel ionized dideuterium cations returning to the grid and heating it.
- Most of the current flowing in the fusor is the anode-cathode electron current generating X-rays.
- All fusable deuterons are ionized and dissociated by X-rays.
- Grid heating contributes to the electron current and thus to the ionization rate.

And if it is correct:

- The resistance heated thermionic cathode should increase fusion ratio and it should happen at lower voltages and currents.
- Very permeable thin wire grid may be not as good as it seams. If there is thermionic emission the tunneling ionization is not needed, as 100% ions created this way is lost and non-fusable. And high energy, accelerated deuterons will not hit the grid that easily.
- External source of ionizing radiation should increase fusion ratio.

That it is. I would appreciate any critique, alternative explanations and pointing out mistakes.
“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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Richard Hull
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Re: Mind twisting riddles of fusor operation

Post by Richard Hull » Wed Dec 11, 2019 4:00 am

Well, no one has stepped up to the plate in response to your well reasoned post and query. As I feel you have put a real effort into the brain work, I will step into the breach. Deep thinking deserves a response.

There are many posts over the years, not necessarily in the FAQs where operation is discussed and re-defined.

1. 100% of all electrons ever created in the fusor are, indeed, lost to thermal heating of the shell, ion and x-ray production.
2. Any deuterons created are by chance encounters with electrons of suitable energy within the nightmare like mess going on in the fusor.
3. 100% of all deuterons will have a "run" at the cathode grid in an attempt to fuse. A vanishing small number will succeed.
4. Academic fusor research at the university of Wisconsin has shown that very little fusion occurs at or inside the grid.
5. The same academic source has found that most fusion occurs outside of the grid in the far larger volume of mess going on in the reactor vessel. This is due to fast neutral and fast deutron collisions (tunneling).
6. We have shown that neutral deuterium atoms ultimately can embed themselves in the walls of the fusor over time, (hydrogen absorption in metals), and that as the fusor is used, these are knocked out and ionized by electron bombardment at the shell.
7. The action in #6 above creates deuterium ions at the ideal location within the vessel, (at the shell), for acceleration to the grid to a possible maximum, and perhaps, fusion energy.
8. In the end, and by any serious examination, the fusor's input losses due to electron and lost deuterium neutrals at the shell, be they fast or slow give up their energy to heat and x -radiation at the shell. Such losses approach an input energy loss of 99.99999%. This is a virtual 100% loss of all input energy to heat and radiation.

The above listing is not complete. One could go on and on, but the above is a list of the most serious issues both for and against its doing fusion at a high level. If one has an unlimited budget, and a good deal of spare time, all manner of significant improvements could be brought to bear. However the beauty and simplicity of the amateur fusor morphs into a serious act of science with serious money and time needed to produce improved results.

Our simple fusor has, in only the last two years, been improved from a 6 or 8 inch sphere capable of no more than 3e106 neutrons/sec isotropic with 60kev applied to similar numbers at much lower voltages and increased pressures in very small device volumes. Still, we are just a simple fusor. One grid of varying types and designs and one simple vessel. We are doing better and keeping it simpler and cheaper to produce results and more fusion.

In short, there are many things that aid fusion in the fusor by many different paths and possible explanations. There are also many misconceptions about how the fusor works that are wrong. In the end, regardless of the research and the intellect that might attempt to explain what is going on and how fusion is actually done in the fusor, it is a fool's errand to try and figure it all out. There is just too much going on in the fusor where some theory that explains to some degree of completeness and finality is just not possible. The fusor "bull heads fusion" It is like ramming a car into a coal face to mine coal. It works, but not enough coal or fusion takes place for all the effort and energy expended

A little bit of this and a little bit of that is the best we might hope for. The result is that the simple amateur fusor does do fusion and that is that. Improvement by an order of magnitude or two in any give fusor type or volume beyond the best done to date, does not seem possible with materials at hand. We are 8 to 9 orders of magnitude from actually producing a net fusion energy result. So any try for that is ridiculous.

To improve the fusor is to improve a neutron source and nothing else.

It is laudable that you have tried to figure it all out. Many before you have and we find that only a bit of this and a bit of that makes any sense and there is no complete explanation extant. What we are left with is a great collection of many possible reasons the device fuses and why its fusion is thwarted by an equal number of good reasons.

I would like to say "go figure", but at best, it is a tortured and never ending mental exercise.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Maciek Szymanski
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Re: Mind twisting riddles of fusor operation

Post by Maciek Szymanski » Wed Dec 11, 2019 7:24 am

Richard!

Thank you for response. I'm of course aware, that the fusor is not capable of net energy production, and I am far from looking for an easy way of making it so. If it would be possible then it it would be done. But the complexity of the fusor process along with the simplicity and easy operation device makes it a fascinating research instrument. The instrument accessible event to amateurs with moderate resources.
Maybe I haven't stated it clear enough, but the conclusions I've made are not ideas for immediate improvement of the fusor into a compact fusion energy generator but rather some clues to investigate ionization mechanism in the simple fusor.

I've read the thread on hydrogen absorption - that is also very interesting topic especially taking in account energy/corss section dependence of electron impact induced desorption, ionization and dissociation. I've not dug into that. Is hydrogen desorbing from metal as atoms or as molecules?
“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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Re: Mind twisting riddles of fusor operation

Post by Richard Hull » Wed Dec 11, 2019 11:02 am

Regarding desorption.... We have no idea if the buried deuterium exits the shell as molecules or as atoms, but the rather intense and very high energy electron bombardment of the shell would certainly allow for many impacts to create deuterons, regardless of molecular or atomic desorption. Remember, the shell collects electrons mostly created at the hot grid during higher power operation. The rather fine wire allows for rather intense fields there. Naturally, the electrons bombarding the shell would have a range of energies, but mostly rather high energies due to their far greater mean free path over deuterium, non-fusing, neutrals slamming into the shell. These speedy neutrals can probably go many layers into the metal lattice, trapping them more securely than chemical hydrogen driven electrolysis. ( a few eV).

While stainless steel is not a great metal to absorb hydrogen, all metals do this and we have electron currents on the order of ten or more milliamperes in the ideal case. The old cold fusion flap used one of the best metals, palladium. Some limited work here has involved titanium inserts as virtual shell based targets or even Ti cathodes! Titanium, as you may know, is a great absorber of hydrogen. No quantitative results are yet known, but qualitative results show promise. With stainless steel (SS), I would imagine the buried resident time with the fusor fully heated and functioning is not very great, however, once turned off desorption
seems to virtually cease or slows a great deal. Successive days of operation see more and more fusion take place each day up to a point. Much depends on the type fusor, its volume and surface area of the vessel itself. This is a rich area for experiment.

I am glad you are interested and questioning with the right type of questions. Sadly the answers I have for you are mostly qualitative to speculative based on my 20 years of doing fusion in the fusor and the many others here sharing their knowledge and experiences, allowing me to learn as well over these many years.

Might I say that your photographic avatar is one of the best here. I see a man who is listening to what is being told to him, but the expression while not totally skeptical, is calculating and weighing and considering all that he hears. No one could ask for a better scientific sense in an image. Occam's Razor is at work here.... Fabulous!

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Maciek Szymanski
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Re: Mind twisting riddles of fusor operation

Post by Maciek Szymanski » Thu Dec 12, 2019 7:30 am

Might I say that your photographic avatar is one of the best here.
It's nice you like it.

I've made a brief review of the ion impact desorption and found the quite informative article (let's praise online access to scientific publications I've at work):

J. H. Leck, B. P. Stimpson Desorption from Gas Covered Surfaces by Electron Impact: A Review of the Subject

And the final reflection. It looks, that there is a lot of interesting and important processes happening on the OUTER shell, while the plasma inside the grid looks so beautiful and promising.
“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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Re: Mind twisting riddles of fusor operation

Post by Richard Hull » Thu Dec 12, 2019 9:48 am

Yes, the wonderful and beautiful plasma ball in the inner grid gave rise to the term "star in a jar", (see my early, (1998),bell jar demo fusor images below). This lovely apparition was, for a long time, thought to be where the real action took place within in the fusor system.

A good while back, I sort of realized the outer shell was a real aid to fusion as well as being the #1 input energy loss point in the system. Had I not once been interested in cold fusion and looked into metal hydrogen absorption, I might not have started saying the shell seemed to store and release deuterium over repeated operation, aiding in the fusion process.

The good, the bad and the ugly is seen to be acting in the fusor. The simple amateur, single grid fusor is not so simple when it comes to realizing and attempting to explain all that takes place inside it. It is a bedlam of physics going on inside. The fusor represents so many aspects of fusion physics at different points over it volume, while being the most uncontrolled and inefficient fusion reactor on earth............Yet it does fusion in spite of its crude assemblage.

The fusor represents the least expensive way to do easily proven fusion and act as a simple amateur experimental source of neutrons for activation.

The Article you submitted is very good. Of course, as the article appear in a vacuum journal, they viewed the desorption as a horrid, negative issue. We however, in the fusor relize it to be a possible contributor to the fusion process. One man's nightmare is another man's dream..

Richard Hull
Attachments
FusorIIjar.JPG
1998 second demo fusor II
FusorIIcomplete.JPG
All in one portable demo system
fusor2star.jpg
"Star in a Jar"
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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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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