Paul, I don't think so...But that's why we do the lab work. Remember, mean free path is right around the size of the box here - funny things happen - the interactions are weak, not like a fluid with the concept of "pressure" at all - grey area between ballistic and viscous, more on the ballistic side. Of course, mean free path is really defined for uncharged stuff. We've yet to have that - or even a neutral plasma, we usually have a huge excess of electrons unless I put RF on the grid, and only that grid, then I see closer to neutral as the positive peaks on the grid draw current and take the electrons away. This is a real pronounced effect.
This one's kinda hard to explain.. Note that some time - a long time - after the ion grid, around 6-8" out from the main grid end (ion grid in the big tank, main in a sidearm) - we get pulses of fusion -top scope trace is the neutron detector (crappy circuit that has dc blocking issues, but the negative pulses are the neutrons). We had DC on the main grid, and an NST hooked to the ion grid via a capacitor - and you just can't drive a grid in there positive much unless you have a LOT of current. This circuit fries NSTs really fast, they don't like those positive pulses on the terminal when they're at peak negative in the cycle(!).
The timings look more like heavier particles, and yes, you're reading that right - the effective C and parallel R
both go UP with density, to the point where as soon as we get anywhere near what most people think of a plasma density that would have ...waves, visible light, and so on, this effect is gone and it looks like a resistor to the grid terminal - with, at slow speeds, the usual negative resistance characteristic of a neon bulb. In other words, it starts acting like a more conventional plasma that might indeed have waves and stuff in it - if we went to those same pressures, we get those same results as the rest of the world - good thing in my view, I know my measurements aren't bunk.
I think we have something new here in the sense of working right between molecular and viscous flow, could be wrong but that's what it looks like - and I can't find any lit that works in this region, it's no man's land. Other measurements hint at ridiculously (ludicrously even for deuteron e/m) long transit times for what we think are the voltages involved, but have been hard to make and be sure of. In the dc + "put an impulse on there so you can measure times" mode, we're seeing at most 5kev on the deuterons by measuring speed - when we have 50kv applied. Sloooooow - and it does point to a more conventional interpretation of a plasma with waves and shielding and all that - or, looking at the geometry and the fact that we don't have the same density everywhere - not, hard to measure, this isn't a fluid in a tokomak, not even close. At 50kev if it were electrons I wouldn't be able to measure the transit times with my 2.5 ghz sampler! They'd be getting relativistic and my distances are short. At any rate, I did try to dupe the measurements I see in the lit for the plasma resonances and no dice in this pressure region - it's just not there. Shielding, dunno, probably yes from what I see, at least some.
I will have to crack the tank (which would be first time in ~3 years - it's REALLY CLEAN in there being pumped to e-7 or e-8 mbar between uses, continuously. What I need do to get those measurements is to have more probes at different distances from the thing I'm driving. Luck of the draw has it that they're almost all close
to the same radial distance, so doing the old distance/time
A-time
B = speed doesn't help me much - the distances are so close to the same I can't be sure of measuring them through the window by eyeball..no way I'd trust that. I'd rather have something like 3,7,20,25" distances or something like that. Which I could have in this tank - the main grid is in a side arm with the end about flush with a pretty big tank "drift space" if I want to use it like that.
In short, we have a far longer mean free path than works in the standard plasma equations stuff that assume hydrodynamic kinds of behavior.
Calculating from the Miley/Murali book
1 for plasma resonance I get around 8 mhz and this should look like an inductance, but nope. At this pressure, "no mans land", there's just not enough interaction for that stuff to apply accurately, you can't assume a smooth fluid kinda thing.
FWIW, I'm saying indicated pressures as when in the lab, it's easy to write that down. Depending on which Pfeiffer document you look at - and here we're in no mans land between where the pirani and ion gages switch - the true pressure for unionized deuterium should be around 1/2 or 1/2.5 the reading. Complicating that is that already-ionized D reads a little higher...just an observation here, they don't mention that.
Now, at the low voltages, (3-4kv pp here) I don't expect this to look the same as at the "Real" voltages I plan to run to get velocities up to hopeful fusion levels. The reason for using this frequency band vs some other random one is that I should (heavy SWAG) be able to get to the tens of kv without hitting tank walls with D's - if I go faster, I can use more HV, slower and I hit the walls with less. Back to the low volts - at this scale, using the math I'm using (ion trap Mathieu stuff) the grid size itself is significant, which messes everything up somewhat. I want to get to 10x anyway of this so I know that's less of a factor and am working on modding a little Ham cw xmitter for that purpose now. It should also allow me to turn off the DC ion grid source, and use that as another faraday probe for timing measurements.
I could alternately drive that around 40 to about 80 khz but that adds a lotta monkey motion to account for in the other test results. Kind a high price for getting rid of the extra electrons, which I *think* higher drive on the main grid will (is) do anyway - and will do better when there aren't so many as the drive on the main grid along will keep it "lit". We have noticed, which I think is in favor of the more "plasma" interpretations - that medium HF takes a lot less to light off, or stay lit. This could just be the usual de-ionization times you see in say, thyratrons, but dunno, haven't checked, hours in the day and all that. We are at lots lower pressure than they so it should be longer...
It seems no math works right in this no man's land pressure range that we have "on average" and "outside the grid" and "away from the time/space of the focus region" which is why I'm doing this lab work in the first place.
We do note near-instantaneous response from the electrons when we try and drive the grid positive, it's a good diode to ground and fast enough that at this frequency range the phase lag is zero (as it should be). I will be taking more measurements of lag time to probe 6" away with drive voltage, all else the same, next run I hope - I need a better RF source, which is in progress. I also have huge, kW and multi kW stuff, but I'd like to work up to that before making too much $moke!
Next test will be with a mere 10 times the power of the last, a reasonable binary-type search, eh?
Probably the most interesting from my POV is that while my mass spectrometers, running at nearly the same speeds/feeds, barf out at around e-4 mbar, and here we're fine at e-2 - 100x higher pressure. Now, if I double that a time or two, this barfs out itself, but there's a pretty big space of ??? behavior in there. And right where I think I want it.
1 I've already just put that book back on the shelf as much of it turns out to be armchair theorizing that doesn't live long in the presence of test equipment, but if you like, the ISBN is: 978-1-4614-9337-2
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.