Fusor analogy to quadrupole mass spectrometer

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Dan Knapp
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Fusor analogy to quadrupole mass spectrometer

Post by Dan Knapp » Sat Feb 23, 2019 2:43 pm

Since I hadn’t seen anything from Doug Coulter in a while, I checked his web page coultersmithing.com. He posted some data at the end of last month on his experiments with his fusor putting RF on the grid. He draws analogy to a quadrupole mass spectrometer, but it’s not clear to me how the spherical field could act like a quadrupole. It looks to me more like he’s repeating the Los Alamos POPS work. Is anyone familiar with what he is pursuing now and able to explain how a fusor could be analogous to a quadrupole?

John Futter
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Re: Fusor analogy to quadrupole mass spectrometer

Post by John Futter » Sun Feb 24, 2019 3:01 am

Having been at Doug's albeit quite some time ago and hopefully not letting ther cat out of the bag
doug is using a side arm of his chamber and most experiments are axial not sphereical.
And I'm guessing here but he is getting reciculation and just like a quadropole mass spec rf freq and dc conditions have to be exactly right to get what he wants
why not message Doug!!
I pinged him a couple of weeks ago just checking on him

Dan Knapp
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Re: Fusor analogy to quadrupole mass spectrometer

Post by Dan Knapp » Sun Feb 24, 2019 3:15 am

Thanks John
I have emailed Doug, but have not yet heard back from him.
I know he was doing some cylindrical geometry work with a cylindrical grid also, but it’s still not clear to me how this could behave like a quadrupole.

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Richard Hull
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Re: Fusor analogy to quadrupole mass spectrometer

Post by Richard Hull » Sun Feb 24, 2019 8:00 am

I wish I could add to this. Doug's main assistant, Bill Fain, drove the 4-5 hours to attended one of our HEAS monthly meetings in January and I asked about Doug's efforts. He merely noted that Doug was still at it and trying some new avenues. No details beyond that. Bill also attended the Richmond frostfest (ham fest) in February and had a portable gamma spec that was pretty cool with him and put it over some of my ore for sale. Again, little response when asked about Doug.

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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Re: Fusor analogy to quadrupole mass spectrometer

Post by billwcf » Sun Feb 24, 2019 4:40 pm

Hi. Doug is having trouble logging in today, but has asked me to post this link until he is able to comment. Thanks. Bill

http://www.coultersmithing.com/forums/v ... f=8&t=1127

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Re: Fusor analogy to quadrupole mass spectrometer

Post by DCFusor » Sun Feb 24, 2019 4:47 pm

Hi guys, it's really me, there's some nasty issue with the board and maybe interaction with chrome that wouldn't let me login, sucessfully use the reset password stuff and so on. So I made this "fake" identity to respond, hopefully the admins will fix the issue so I can be on as Doug Coulter again.

I'm using the same *math* as a quadrupole mass spec, or for that matter a regular ion trap. For the latter, the symmetries are about the same, though the regular trap has just one axis of motion, with my cylindirical symmetry, it works out as about the same thing, just radially.

The TL;DR is that, yup, it works, subject to the limited testing I've managed so far, and some things we knew already, such as the fact (As Richard once said) we normally make our ions near the bottom of the potential well - are true, but possible to work around. Another thing we knew - measured here, is that anything like a reasonably dense plasma "smears" the field we apply, and the net result is that when we measured propagation times of D+ in the tank, we found they were moving with around 5kev speeds - when we were putting on 50kv....

A quadrupole mass spectrometer is using an operating line just *outside* where the Matthieu equations of motion are stable....we don't need to be terribly e/m specific here, as all the other stuff present is WAY different than D+. So I picked an operating point in the middle of stability for D+. It will still easily reject H or He for example (and I don't care anyway, I'm just wanting to keep the D). Most ion traps, same deal - run on the edge to make sure you only keep one species, which is hard to get right up in the high mass stuff, which is of no relevance to what we are doing with deuterium.

The failing of the math is that it doesn't take into account the inter-ion coulomb interaction at all - the assumption is that things are so sparse there isn't any - and this is why a mass spec fails pretty hard at e-5 millbar or so. We want to run up around something*e-3 mbar to have enough stuff there to get fusion and be in some managable part of the Paschen's law curve.
(I'll put some links below to all this).
I wrote a small perl script to let me pick the "a and q" values of the Matthieu equations of motion this stuff all uses, which lets me plant myself in the middle of the stability region - but still for the bad assumption that there's no coloumb interaction. But you gotta start somewhere....
And I have this neat toolset of data aq and display that helps me fish around for sweet spots and see trends really well, so....I just dove in and tried some things.
This link is the best "easy one". https://en.wikipedia.org/wiki/Quadrupole_ion_trap Note especially the picture of where the curves cross for trapping ions. These are all "reduced variables" which means basically that there are a lot of combinations that will work - if you increase the voltages so things go faster, you have to use a higher frequency and so on - too much velocity for the frequency, and things hit the tank walls - you have to get it so things stay in the tank, but do go outside the grid so they can come back going fast to fuse. What I brought to the table was saying, nope I don't want the easiest way to trap D+ "at all", what I want is to trap it but make them go fast enough so they fuse when they hit, so I'm using a lot different values (that still satisfy this math) that give me that. Notice in this picture (in the link above too) https://en.wikipedia.org/wiki/Quadrupol ... bility.gif that most traps operate just outside the overlap region of stability - they want the desired species to just barely make it to the detector before being rejected.

In a fusor, we want to keep them as long as possible - for re-circulation, which in at least my thinking needs to be driven continuously, just like any spring-mass system, due to losses. As in "my guitar doesn't pick itself just because I apply gravity along the desired vibration axis" which is kind of what you're doing with a DC drive fusor. In that case, the only reason it works at all is because new ions are being created and old ones recombining, which as we know, winds up being very bad efficiency.

Proof is in the pudding, and TL;DR, it works and with 25kv DC plus 8kv AC in a system at 2.9 mhz...I get better net Q than I do with 50kv DC, which was already pretty good by fusor.net standards (7-12 million n/s for 50kv and 12 ma for the "normal" case).

I'm not getting anywhere near that many here - I want to live, so I've been running things right at where it barely produces fusion - in the 100,000's n/s for now. But the math says "gimme some limits and I'll give you some numbers". I just put those limits at "just barely work so I don't die" as this is hard to remote control at the moment.

So, the pudding as it exists so far. The Q was going up as I was going off the edge of the plot - and faster than exponentially, so right now this is all being rebuilt to help me find a peak, or have enough drive to overcome the aforementioned "smearing" or maybe Debye shielding we see in plasmas with enough density to be useful. I don't edit my data, and in this run I was also just twiddling some stuff to see if there was a sweeter spot near by, as this software makes that easy to analyze. There's some interesting stuff at higher voltages, but this could be noise due to arcing setting in. Any big stuff with "zero drive" is basically a flavor of the divide by zero issue when computing Q and the power is off...cosmic rays. So, relucantly as this might be misinterpreted...here's the pudding.
The lines along the 25kv axis are the real deal. The flat one is DC only, the nice one curving up is with the AC added.
Some interesting stuff at higher DC voltages, might be legit, might not be - the bypass cap I was using to prevent back-feeding a rather expensive Spellman (Which has been great all along, all props to CliffS), started arcing. Anyone who wants to help this can come up with something like 2500pf at something like 50kv and I can move higher for exploring...
Here's a link to the work in progress on my board, it gets a little OT there, but the data is there, including how I'm getting AC and DC both into a fusor.
I am, BTW, using a separate grid out in the main tank to provide ions at pressures lower than the main grid will keep things going by itself.
http://www.coultersmithing.com/forums/v ... 6627#p6627
Is the middle of that thread. All are welcome to fish around - my place is open source too.
Last edited by DCFusor on Sun Feb 24, 2019 5:21 pm, edited 2 times in total.

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Re: Fusor analogy to quadrupole mass spectrometer

Post by DCFusor » Sun Feb 24, 2019 5:06 pm

Here's a quicky "just write this up" perl script that I'm using. I picked numbers for a and Q that looked like they were in the middle of the good range, but this assumes no other Coulomb effects, so I *know* it's wrong. But again, you have to start somewhere. I'm extremely gratified that it works in fusor conditions at all - around 100x where the usual mass spec craps out completely. With added terms to the math, it should keep working right up to "oh wow" ranges. At least I think so. http://www.coultersmithing.com/forums/v ... 096&p=6420

There's a bit more background there. Pretty dumb code, I just made it work real fast (eg in programmer time), didn't optimize for purty. So if you have linux with perl available, you can play too. (you can run perl on windows but it's a fairly major pain to get any extra modules in there - this doesn't need them but be warned, my other stuff makes extensive use of metacpan - and FWIW, it all runs on things like a raspberry pi to).
Anyone who wants a copy of the database(s) I use just needs to send me a stamped, self-addressed storage device or a link to a place I can upload it to. There's rather a lot of it....dcfusor@gmail.com is how to get ahold of me.

And here's some more explanation of the whole AC drive thing which I'm re-purposing for re-circulation. Remember, that with cylindrical symmetry, there are two directions - out and in - which easily mentally map to say, up and down for a single axis trap.
If you think about it, this makes any scattering not matter so much - all directions from the center are "out" and it'll be pulled back in from any angle...

Oops, "file too large" error...
It's on my board on this thread: http://www.coultersmithing.com/forums/v ... 124&p=6611

What I'm doing now is building a somewhat larger and more robust RF source and matching network. It's exciting when it's getting better as you run off the paper (or it won't stay lit, which is the edge of the paper here) - but obviously, it means the peak hasn't been found yet. So, with higher voltages to counteract the smearing or shielding, maybe I can get that peak back on the paper and find out how good it is, and maybe even contribute the new needed terms to the equations of motion. That'd be kinda cool.

Dan Knapp
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Re: Fusor analogy to quadrupole mass spectrometer

Post by Dan Knapp » Sun Feb 24, 2019 7:15 pm

My apologies for being slow to comprehend, but it would be very helpful if you could add a sketch of your geometry and how it approximates a quadrupole trap.

Roberto Ferrari
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Re: Fusor analogy to quadrupole mass spectrometer

Post by Roberto Ferrari » Mon Feb 25, 2019 12:43 pm

What bothers me of this approach is the high vacuum required for a working mass quadrupole or ion trap.
Seems to be far away from the fusor typical operating pressures.

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Doug Coulter
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Re: Fusor analogy to quadrupole mass spectrometer

Post by Doug Coulter » Mon Feb 25, 2019 3:45 pm

Yep, amazing, isn't it. I believe the reason is that when a normal trap or mass spec runs, it's on the very edge of the stable region - even the particles you want to detect are eventually rejected with a quadrupole's normal operating line. (I used the word believe as I haven't proved it yet - ) I did link to some plots of the operating regions here, wikipedia, and on my site, the latter fairly extensively. Mass specs don't even run in the stable trapping area, they run just outside it, and some of the ions you want fall out! This is to get more resolution, discussed in detail in the source material.

Here I use a different part of the workable region - I'm not sure it's the best part, but there's a long and continuous tradeoff available between resolution and effective aperture (defined in this context by Dawson's as how picky the thing is about input velocities and angles). You'd have to read the book, which sadly isn't the least bit inexpensive - not sure how much of it I could put online before I'm in some kind of trouble. One point I've been making over and over, seemingly to people going "la la la, I can't hear you" is that all the literature and theory assumes that

1: there's not enough ions to have any space charge effects - true in a mass spec, but dead wrong in a fusor, and

2: the only thing we care about is...mass specs, rejecting things that don't have the exact e/m we want, even seeing stuff like the binding energy mass deficit in this or that nucleus tiny fractions of 1 atomic number in something that weighs 10's of them. A ridiculous requirement for a fusor.

Wakey wakey - we don't care one bit about either assumption here. We want LOTS of ions, almost no selectivity/resolution either - we wouldn't need much to tell H from D or He, or T, even if we cared, and we don't - there's not much of those there anyway.. We just want to use the equations of motion (or the required variations that are going to need more terms) for our own purposes.

Also, lots of geometries "work" for one purpose or another - he shows two pages of dinky drawings of shapes and arrangements that work in some sense to trap ions - all using the same equations of motion (but maybe some stuff is turned sideways, roughly speaking). Don't fixate on just one that happens to have all those properties we don't care about!
From AIP Press, Peter Dawson ISBN 1-56396-455-4
The whole point is by wiggling the field, you can get ions to oscillate around some location. If you do that right, you can have containment in a volume, which turns out to be far easier than at a motionless point (that repulsion thing) - and in our case, deal if a lot of the motions to and fro result in collisions.

While a radially symmetric field only has "out and in" from a particles point of view, when we look at it, we can see that moving "in" from the left, (or top) could result in a collision with something moving "in" from the right or bottom (or any other head on combo). With this symmetry and a large aperture, a lot of the effects of scattering appear to create less loss, because if a particle would have gone "out" of a grid going up, going out to one side instead doesn't matter in this geometry. A big aperture means that the exact velocity isn't as important to not losing the particle as well. Remember, when we're talking about scattering, even Rutherford had problems with small angles, as they are far more common than large ones (eg really good collisions nearly head on) - he had to adjust source strengths and do other things to stay within his measureable dynamic range. A regular scheme loses those small angle scatterers. This would not.

I was myself quite surprised that it's working better than DC by a large factor, and at ~100x more pressure than where my mass specs just lose it.

Without the clues kind of handed to me by having something like this happen more or less by accident, I'd not have even pursued this.....FWIW, I'd had something like a blocking oscillator going when I had a roughly 1.8 mhz resonant circuit in my HV feed, so that thing was ringing pretty hard, and producing a kind of pulsed version of what I'm now doing continuously and on purpose. Looking at the wiring on Farnsworth's old machines, he may have also done this by accident with parasitic L and C, which would explain both of us seeing some anomalous output (or we were both dreaming). Difference is, I have really good data aq compared to what he had, so I had data to look at and try to reproduce...I have a video on my youtube channel called "unstable" that shows an early version of this happening more or less by accident, and even with bursts shorter than my counting interval, showing me more neutrons/second than I was then getting with full stable DC drive. A lot of this work was from the attempt to explain how what I observed could be true, no magic allowed. I know many didn't believe it, but I didn't have that option - I was there, I saw what I saw.

The thing about science is that it's reproducible, and your belief or understanding (or lack of them) isn't what makes things work.
To paraphrase Isaac Asimov - "you don't have to guess which altar the fire's going to come down on anymore".

This works and reproduces. Now, how far I can take it, dunno - news at 11, if you get my drift - this is ongoing work. It is crapping out badly as I raise either pressure or really, the density of ions, at least with this set of numbers (F,U,V in the lit). We also notice something similar with pure DC, however, when we look at achieved ion velocities vs applied field. It goes to heck in a handbasket at higher pressures - the same is likely true here, and that space (the drive parameters vs pressure) will have to be explored, which is a lot harder with this mixed signal than it is with DC, but hey...if it was simple, everyone would have done it already, right?

I think part of why this works at all is the mean free path variation involved. Out in the space well away from the grid, there's more volume for things to be spread out in, and the mean free path is bigger there even when most of the ions are out there - and to the extent they interact with one another and/or neutrals out there, all that does is re-uniform the distribution in space so conditions for the next pass are nicely regularized - and all while things are slow and at low energy, so loss is low too. Near focus...mean free path is shorter by quite a bit when everyone is arriving at the party. Quality of electrostatic focus is very good in my lashup, far better than possible in spheres, FWIW. The poisser at my line focus is on the order of << 1mm, maybe .3 mm or so....
Why guess when you can know? Measure!

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