New nozzle

Well, the disc has yielded some interesting results, but not the ones I'd like. I'm able to form a stable cloud above the disc, but the negative charge that the disc acquires repels the negatively charged particles and prevents them from moving through the nozzle. We took out the plate yesterday and increased the hole size from 0.13 inches to 1 inch, and now I was able to get the cloud to pass through the nozzle; the conditions under which I can do this, though (higher pressure and high voltage) don't allow me to form dust acoustic waves. Otherwise, under conditions that allow me to form the waves, the cloud remains at a fixed distance above the plate, and moves up and down to maintain that distance when I raise and lower the plate.

My mentor and I had two ideas for moving forward. The first was that we could increase the nozzle's diameter even more; this would let us get the cloud in the nozzle more consistently, but at that point we may lose the compression which we hoped that the nozzle would provide. The second was that we could paint the disc black. We aren't sure what exactly this would do, but it was something that was present in the experiment we are trying to emulate. It's possible that the paint was only present there to minimize reflection of the laser; in that experiment the laser shined directly at the nozzle, while in ours it is parallel to it, so reflection isn't a problem. However, the paint would have electrically isolated the nozzle from the plasma; we are unsure of the effects that would cause.

We consulted my mentor's boss, and he suggested that since the problems might stem from the wide disc interfering with the plasma, we could try eliminating the rim by using a washer or something similar instead of the wide disc. We thought it was worth a shot, so I looked at the stuff we had around, and ended up using a copper gasket as the nozzle. Gaskets are an alternative way to seal chamber openings: instead of placing a rubber O-ring between two metal flanges compressing it with screws, a copper ring can be placed there; knife edges on the inside of the flanges press into the gasket as the screws are tightened, producing a much better seal. A copper gasket can only be used once, though, so we have a lot of used ones lying around.

I doubt we will get shocks from this immediately, but hopefully it will give some insight into where we should go. At the very least, it will eliminate one variable (rim size).

Even though I'm getting the results I want, I'm pretty happy with my construction; it's somewhat annoying to untie and retie the plate while trying to keep the fishing line in the grooves, but the rod itself works great. Without being able to raise and lower the plate under vacuum, it would have taken me several days to confirm that the cloud maintains a constant distance from the plate, compared to a minute with this assembly.