Here's a manly plasma tube, coming out of the '85 Plasma Kinetics model 451 copper vapor laser. The tube is 78" long with the center section being 6.5" diameter. The bore looks like 2" and the windows are 4" diameter. Only way I can get the covers off to hammer them back into place is to take the whole thing apart so I can move it around.
For contrast, here are the smallest plasma tubes in the collection. Smallest is about 4" long, probably from a gun sight or other pointer.