Best example of Alex Petty circuit.. him have understand the way but forget ground inside water (casually?)
Jean Naudin instead have added the dielectric around inner electrode
However for obtain best results you need AC/DC (rectifier diode) heterodyne circuit.. suggest to use half-bridge driver simple and functional
Merge all of these togheter and you obtain right process.
WFC can be designed differently for semplify and amplify the electron cascade and for solve high voltage discharges inside.
Remember that WFC in fact is an capacitor with metal around.