Unstable plasma and other thoughts

I think I know why I'm having problems with my waves now that the probe is back in. The probe seems to be pushing the cloud downward, and the large grounding plate I installed is increasing the cloud's size and thus lowering its lower edge. Since the cloud is now much closer to the grounding plate, arcing between the plate and cloud is more common. The arcs are also smaller and more frequent; normally arcs are brightly visible and occur every few seconds, but now they're on the order of 4 per second, and too weak to see. It's pretty frustrating to record what seems to be a good wave, only to see when I play it back that it is unstable. Since the arcing frequency is fairly consistent, my mentor recommended simply removing that frequency (ie 4 Hz) from the resulting wave; I'll try it, but I think that the instability has farther reaching effects that will influence the data. The solution will probably be to lower the grounding plate; I'll do that tomorrow afternoon so the vacuum can stabilize over the weekend.

On the topic of instability, I filmed a pretty odd effect that occurred fairly regularly at certain conditions. A strong plasma glow would appear suddenly on one side of the bottom electrode, pulling the cloud towards it and stabilizing it. Then it would disappear, and the cloud would return to its previous position and resume oscillating.

I'm not sure what's causing it, and neither is my mentor; she says that it may be a result of dirt on the lower electrode, but from what I've seen, that results in a steady, concentrated glow around that area, rather than a wide glow that appears and disappears like in this scenario.

I've also found the problem I was having with the probe. The square wave I was generating was apparently only 1 millisecond long, when I'd assumed it was 10 milliseconds long. Anyway, that's another variable I will need to play around with tomorrow before I move the plate. I haven't yet tried other waveforms, so I'll need to do that too.

I spent far more time than I should have this afternoon battling a persistent bug in my wave analysis code and a separate one in my GUI, but managed to fix (more or less) both of them. Since most of my time before lunch was taken up by a seminar and an evacuation drill, I didn't spend as much time working with the dust waves as I had hoped.

My clouds are getting frustratingly faint, too, and I can't see the dust in the wave valleys at all. This isn't really anything new, but it means I need to spend more time trying to get bright and dense clouds. Near the beginning of my internship I talked to someone who was in the process of building an image intensifier, and who said that they should be done by the end of the summer; I should find out whether any progress was made on that and whether I might be able to borrow it at some point (although if I remember correctly he offered to let us use it on the condition that we helped him build it...). Unless we do end up getting one of those devices, I'm still ultimately going to be limited by my laser power. Another option is to adjust the cloud density; dense clouds are brighter, but the density is mostly fixed by the particle characteristics. I probably won't be switching to a different dust material, but I could filter the dust to get a uniform particle size. That would probably change the characteristics of the cloud significantly, though I'm not exactly sure which ones and in what direction.