The gap is adjustable when running, and usually I need to move the electrodes close together to start a discharge, and then widen the gap. That could be replaced with an ignition arc circuit but I haven’t bothered with that yet. The rubber stoppers are very lightly lubricated with silicone grease to help the vacuum seal and allow gap adjustment without a fight (which can result in a shock). The vanilla bean tube is strong plastic. I tried glass tubing but it broke quite often at the stoppers. The vacuum can suck the stoppers in, which then breaks the glass. (Etching the glass at the ends might help prevent that).
I have a scintillometer here with a 4.5 ci NaI crystal but haven’t tried it near the arc.