An unproductive day

I spent most of today fiddling with the probe and plasma parameters, but I wasn't able to get a non-arcing wave today at all, unfortunately. I did move the grounding plate down a bit, but I needed some materials from certain people all of whom left early, so I wasn't able to move it down as far as I wanted (I needed a new nylon screw to cut to a shorter length and thread with a die, but ended up just moving the plate down half an inch on the screw already in the chamber). By the slow speed at which the vacuum is going down now I suspect I may have introduced a small leak in the chamber, though it could just be outgassing from water vapor as before. I doubt that the short distance I moved the plate will have much of an effect on improving the arcing problem, so I'll probably have to bring the chamber up to atmospheric pressure again on Monday to switch to a new screw. Since I have nothing else to talk about, I'll mention another problem that's stumped me (and my mentor). The setup is mostly symmetric: our electrodes are circular and share a common axis, the chamber is cylindrical (with also the same axis), and the grounding plate, which used to be circular, is now a rectangle that stretches the width of the chamber. The probe is exactly in the center. The laser itself should have no effect. So why, then, do we regularly get a smaller, secondary cloud on the left side of the chamber (near the laser), and not on the other side? We thought it might be a slight tilt of the electrodes, but twisting them didn't drastically change the location of this second cloud. The only other thing I can think of is the place where the electrodes come through the chamber wall, as this is off-center, but those pieces are fairly small and insulated. It's not a question of any particular importance, but I thought it was an interesting quirk.