Latest fusion upstart

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Re: Latest fusion upstart

Postby Doug Coulter » Wed Nov 29, 2017 7:31 pm

I did just that, but the hardening "broke" the easy oscillator, which was touchy to make happen as it was. I can only assume reduced parasitic inductance caused that change.
Rather than fool around endlessly with coil turns ratios and so on, I decided to take some measurements on transit times and phase during changes and just drive the thing.
Now, I may go back to square one, you never know, but since it's kinda hard to "tune" that stuff remotely, it would involve endless back and forthing to tear off the EMI shield, change something, put it back, run the checklist again at the remote position...repeat.

I know some rather surprising things I didn't know before as a result, but only time will tell how things end up, eh?

I did find something new but obvious in hindsight. At the pressures we're running, with the current ion source (which I like the best of all tried) we are not seeing a lot of space charge effect out in the bulk tank. We do start seeing it late in a driven "cycle" when they're all close to the grid instead of spread out all over. We also saw that with effective pressure in the sense of molecular vs viscous flow in some earlier experiments, so in hindsight...duh. But in some ways this simplifies a lot of math, and also tells me some things that weren't directly easy to measure. So good.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Latest fusion upstart

Postby Bob Reite » Thu Nov 30, 2017 5:12 pm

Ah! If you did not have the "EMI shield" on it before, adding that increased the capacitance and thus lowered the resonant frequency. It may well have killed the actual parasitic oscillation that produced the "Gonzo effect".
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Re: Latest fusion upstart

Postby Doug Coulter » Thu Nov 30, 2017 7:13 pm

Right. But that's not all. I've run a number of lashups. The main thing I did recently was remove around 6 feet of ungrounded HV cable, that was a half-turn loop, with the ground return through the rack, instead of that cable. Now the cable, which was coax, is grounded right at the tank as well as at the supply.
Running without it that way...every computer in 10' goes up in smoke, connected or not, due to EMI picked up on the mouse cable or whatever. Not likely I'm willing to spend another few grand replacing those "in the hopes" - and pointless if I lose the data again anyway.

So, self resonance could have gone either way, actually, as it was largely inductance I removed, and capacity I added (which I've tried without).

Worse yet, all this stuff already had other self-resonances, this was on top of those, there was never a single frequency that something was resonant at.
If my theory is right - that's important, as the waveform you'd use to bunch ions is a heck of a lot different than the one you'd use to bunch and attract in electrons (frequency factor ~~ 60?). You'd need more than one to do this according to the simpler version of the math. Nothing narrowband need apply here.

I'm getting ready with some tests to capture a bit of the landscape though. It's a hard slog since with what I have, while I can have two resonances, still, both are sines...if I need an exponential fall followed by a super fast kickback...and don't know the timings - it's a case of setting up something for each octave on each side of that for every test. No, I can't just use inductive kickback to get "super fast" as there's still parallel parasitic C that would have to be resonated out. And then it's not a spike, it's a sine...

Some ringing after is probably fine if I do the rep rate slow enough to let things die down and re-uniform themselves - that was the plan all along anyway.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Latest fusion upstart

Postby Bob Reite » Sat Dec 02, 2017 9:11 pm

I just have a hunch one might get it to work with two sine waves, one to resonate with electrons, the other to resonate the deuterons. I'm going to try it once I finish a couple of projects that help pay the bills around here.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Re: Latest fusion upstart

Postby Doug Coulter » Sat Dec 02, 2017 11:30 pm

We kinda share that hunch - at the least you ought to be able to beat a couple and see interesting things at the beat frequency. But two sines would only work if there was no other interaction, which my measurements show not to be the case when things get "tight" in a bunch. So, rather than straight up ion trap or quadrupole mass spec math (Mathieu) it looks like a little more radical stuff needs to happen here. The accelerating potential would have to increase more than sinusoidally as things get bunched in the middle, else the *net* field would be near zero from the charges you're getting to bunch up.

The required frequencies change depending on the amplitude of the drive...just like the Mathieu stuff. The bigger the drive, the quicker things happen (more or less).
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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