A problem of McMillan on conformal mappings

A halogen generator produces a halogen sanitizing agent to sanitize water in a spa or other water feature. A coaxial wall fitting desirably couples the halogen generator to the water feature. The halogen generator desirably includes a bipolar electrolytic cell in which a center electrode plate rotates between stationary anode and cathode plates. The bipolar electrode includes a plurality of vanes which motivate water flow between the anode and the cathode. The vanes on the rotating electrode also produce a flow of water through the generator. In this manner, the bipolar electrode functions as a impeller to pump water through the halogen generator. The vanes are positioned between the electrode and cathode, and are sufficiently spaced from the cathode to inhibit scale formation on the cathode. The vanes, however, generally do not contact the cathode when rotating. The rotational direction of the electrode relative to the cathode may be reversed periodically and/or the gap spacing between electrode and the cathode may be decreased periodically to enhance removal of scale.