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.