With electrostatic induction, a ring will 'see' an ion filled bubble when it's at a distance of two and a half times the radius of the bubble. Anything greater than that is considered as infinity, electrically. Two rings have to be spaced a little more than two and a half times the diameter of the bubble sitting between them, in order for the rings to be discharged. If the bubbles are tightly fitting in the riser tube, the rings can be spaced at two and a half times the tube diameter. And this spacing is between adjacent edges of the rings, discounting the width of the rings. The number of rings is limited only by the length of the riser. Which could be dangled from a tall building or even a high altitude balloon.
This thing will either never produce enough energy to generate it's own bubbles, or the bubble stream will require only a specific number of rings to close the loop. Even if this number is large, many more rings can be added. Apparently, the charge on the ions doesn't leak off, or else the bubbles would shrink, due to less Coulombic repulsion.