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Fusor Master's Thesis

Posted: Thu Jan 31, 2019 5:34 am
by Joe Gayo

Re: Fusor Master's Thesis

Posted: Thu Jan 31, 2019 5:43 am
by Joe Gayo
Charge exchange cross section data:

Charge Exchange Mean Free Path of Deuterium Ion and Background \ Hydrogen Gas, Data from Nuclear Fusion 10 (1970) p147

I extracted the points from the above article and used Mathematica for a non-linear curve fit -

Code: Select all

modelsol[x_] := Exp[-35.26659743591572/x^0.12476964001522374]/x^3.645879839797641;
x is ion energy in KeV and modelsol is cross section cm^2/N

Re: Fusor Master's Thesis

Posted: Thu Jan 31, 2019 8:38 am
by Rex Allers
Slight warning for those downloading the pdf, it's 38MB in size.

Joe, great to meet you this evening. Hope you continue to stimulate us with well thought out concepts and testing.

Per my mention of difficulties finding stuff with search engines these days,
I looked for "Charge Exchange Mean Free Path..." that was your data source and found nothing matching from any way I searched on a few engines. Wondering where you got access to it?

On your curve fit equation, do you think we can trust the accuracy with only 16 decimal digits in the coefficients? :-)

Re: Fusor Master's Thesis

Posted: Thu Jan 31, 2019 3:20 pm
by Joe Gayo
I really enjoyed our conversation as well.

Here is the link to the second paper:

Re: Fusor Master's Thesis

Posted: Thu Jan 31, 2019 5:41 pm
by Rich Feldman
For those not downloading the paper, Joe explained charge exchange over the table last night. If I got this straight:

Consider an accelerated deuterium ion traveling in rarefied mostly-neutral gas.
Joe's reading points to surprisingly large cross section at, say, 5 keV for a charge exchange (electron shell reaction) that neutralizes the original moving particle and ionizes the original stationary particle. I don't know if this is for atoms or molecular D2, before or after. :-)
He concluded that the Mean Free Path for that is pretty small for fusor dimensions and conditions.

Is that sort of right, Joe?

p.s. Doesn't "charge exchange collision" also sort of apply to the multiplication in a GM tube or proportional counter, unlike in a PMT ?

Re: Fusor Master's Thesis

Posted: Thu Jan 31, 2019 6:12 pm
by Joe Gayo
Correct. The average ion energy is greatly reduced by charge exchange (CX) and it’s correlated by the forums wall loading observations. The glow discharge fusor is dominated by fast neutral fusion and the charge exchange mean free path basically eliminates ion recirculation.

Lower pressure limits density in glow discharge approaches which is why ion guns are superior. However I’m pursuing another approach... size. Building a device that is smaller than the CX MFP at glow pressures. Point of clarification: I use standard KF40 flange interfaces in my device but the chamber is machined from a block of aluminum. The internal volume is smaller than CF2.75 or KF40.

Re: Fusor Master's Thesis

Posted: Thu Jan 31, 2019 6:51 pm
by Richard Hull
I believe in past posts over the many years, re-circulation was found not to supply any significant fusion possibilities. An ancient paper from U of W did an experiment that proved the bulk of fusion is done by fast neutrals. (2000 time frame).

The wall deuterium lattice storage over time seen for the past 7 or 8 years is also a factor in maxing out fusion in any size fusor in daialy operation.

Finally, over the past 3 or 4 years we have seen tremendous gains in fusor devices of rather incredibly small size. This was not by design or any theoretical considerations, but due to sheer poverty of some would be fusioneers who could not afford bigger and more fancy chambers! These small 2.75 crosses and tees have allowed for lowered MFP, higher pressure deuterium operation and a far more efficient chamber wall storage result.

All of the above has been done by actual experiment.

Joe has voiced all of this nicely and attempting to give the past results a sound footing in theory.

I liken all of this discovery to the "lucky donkey effect" that I have spoken off so often in these forums..... Becquerel and Roentgen were lucky donkeys by the sheer "doing" and following a totally different path to work towards a completely different goal. They stumbled over science that would require years of careful theorizing to explain in a cohesive manner.

Richard Hull

Re: Fusor Master's Thesis

Posted: Sat Feb 23, 2019 10:23 pm
by William Pete
Really enjoyed this article and I think it solves a big problem with fragmentation on Fusor, that being said I still have more reading to do.

In humble comparison to some of the other threads on this site, I can see quite clearly in section 4 how to build a fusion reactor and how the author of this article achieved their results. On the other hand when I first joined Fusor - I had to do quite a bit of disoriented digging to find somthing like that diagram depicted in 4.1

I think it would be really cool if the mods would start directing people with curiosity that they would like to take beyond just reading to papers like this (maybe not exactly this one, I'm sure there are many out there regarding this topic)

It just seems like a little bit more linear approach to getting where you are trying to go with this type of research or project for some.

Good find and cheers.

- William

Re: Fusor Master's Thesis

Posted: Sun Feb 24, 2019 12:12 am
by Richard Hull
Agreed! I have placed the above initial posted paper in the theory forums FAQ. It is a good one.


I found the second paper a bit puzzling based on the reduced pressures used and the fact that the D2 in a fusor at 10 microns far outstrips the molecular amount of trace gases in the second paper. Yes, it does occur, but is it significant for amateur purposes? Certainly it is a limiting factor in any IECF system, regardless of design and just piles on to the list of why IECF will just not work for power ready fusion. (which is what the paper was probing.)

Richard Hull

Re: Fusor Master's Thesis

Posted: Sun Feb 24, 2019 1:53 am
by Rex Allers

Re: "disoriented digging"
In the new user chat area I recently posted a link to an earlier post I made with tips for using the FAQs. ... 504#p81504
One key suggestion was this:

"It might be good to start by reading, in each section, the topic names that begin with a number (#1, #2, ...). These should cover a good amount of the basic help."

So, just now, I went to the FAQ part of "Fusor Construction & Operation" and scrolled down to find...
Post by Richard Hull » Wed Feb 28, 2007 9:31 pm ... 674#p12184

Scrolling down to the end of that first message is
"schematic - new fusor.JPG (83.04 KiB) Viewed 11741 times"

That diagram looks a lot like the paper's Figure 4.1 except the forum one has more details and requires reading the text to figure out what the options in the various boxes are.

Maybe something like my FAQ message should be made into a FAQ on FAQs?

BTW, no big deal, but the paper's Figure 4.1 shows the roughing pump and turbo pump connected in reverse order.