Ions look like a lossy capacitor

[Doug Coulter]

So, I set up a test to look for Landau damping or whatever I might see, this time using a trigger on the RF input (cap coupled from the ambient, it's LOUD) and two faraday probes, on the faster, multichannel scope. And...hmmm, that's funny, but no big revelation so far.

The setup is that the trace marked as faraday_b is the one closer to the main grid. Faraday_f is at the front of the tank (Which in this case is also "far").
I note that yes, there is damping of the bunched signal that the close one (_b) sees, compared to the one far away.
I tried with the DC ion source both on and off - you can tell when it's off as the DC levels on the faraday probes are more positive, and in fact I had to change the vertical positioning of the back (near) one to keep it on the screen at all. Note that not only does the amplitude of both change, but the delay between them (the prop or transit time) changes too. Hmmmm.

The DC ion source is kinda out in the middle of the tank, almost between the main grid and the front (far) faraday probe.

So, just the facts, maam - I haven't worked out any particular meaning, other than with the ion source on, there's probably more of them, we know there are more electrons then, and it seems bunching is reduced, damping increased, and prop time shortened with ion source on.

Ion source on

ion source off - note DC level on ch3 especially

So here we are seeing the disturbance in the force (couldn't resist) with ion source on vs off. And how things do indeed damp, and do so differently, as a function of distance from the main grid, which I'm driving with a sine at the frequency indicated on the scope.
And it still looks like this with the ion source off:

with ion source off..and nighttime exposure settings

We lose color when it's so dark, the cam is trying as hard as it can. And I was just too slow of mind to take another with the ion source on etc, I may go back there while it's all still "hot" and get another.

Even with 20-30w in this is pretty hard to get the main grid lit with, even with the ion source on, I usually have to to up to 3 e-2 mbar or so to get the RF part going (the ion source will start down to 1.9e-2). And it wants to go off easily. Part of that is that this RF source is a tuned thing and anything that jiggles something off resonance reduces the net voltage on the grid, it's touchy even though the RF in the shack indicator looks like it's going to create shrapnel any second.

I'll try for some more pix, and maybe even this time remember to get an estimate of the voltage. It's higher than it was without the little Knight-kit inline, but I'm not detecting neutrons at this point with this.

[Doug Coulter]

So, a little more data off (what I hope is) the same lashup- things seem all too variable on this just now.
Some regular camera pix for "color".

Neon bulb "she can't take much more"

The overall thing with some cam shake (sorry)

Looking through the front window

Now, some gridcam pix. With the ion source on, there's enough light to at least see faraday_b well - it's a 2.4 ghz groundplane antenna in another life but serves as a probe here.

Everything is on. Faraday_f is out of the picture but closer to the camera, would be in the lower right if it was in the frame.

A bonus 4ch scope shot with all the signals overlapped so you can see the obvious delays. Ion source was on I think.

Seeing bunching, delays, and damping

And...I'll save myself a file conversion and just say that we only had about 4.5 kv pk-pk here with ions present. We were just off the bottom of where that little knight-kit source would tune well, and things all have to resonate for it to make more net volts than the broadband-flat 50 ohm sig generator alone it seems....I need to push some coil turns closer together or add some capacity in the pi network. Or add some turns back to the beaker, or all of the above.
Or something. The resonant nature of this along with the matching caps adds more variables than I'm completely happy with, but at least I can direct-measure what winds up on the grid itself.

Strangely, the DC offset as a proportion doesn't seem all that fixed - it seems a little different run to run, and I need to look into that as it may give me some more understanding of what's going on.