You may not want to slow down the charge carriers for maximum efficiency. Apparently the device is a neutral charged beam now, but can it be modulated to high frequency AC, such a by passing it through an alternating magnetic field?
If so, there is the possibility of using the Farnsworth style multipactor effect for very high efficiency. This has been published before as a direct conversion scheme for hot fusion. A type of multipactor collector was patented 80 years ago by Philo Farnsworth, the inventor of television, who attempted to take advantage of it as an amplifier. It was so extremely efficient (99+%) that Farnsworth thought it could be made to be gainful, so we have talked about it before on Vortex. There is no independent proof of gain but in some of Farnsworth's papers he claims to have seen real gain ! More commonly in modern EE, the multipactor effect has become a dreaded problem, especially in microwave waveguides - to be avoided at all costs because of runaway amplification of negative charge. In general the multipactor (of the useful variety) will convert kinetic charge carriers by secondary electron emission caused by impact, and if this is done in resonance with an AC field, it leads to exponential electron multiplication - thus the name. But it is easy to get charge cancellation too. Whether it will work for EHD or not, I have no idea. From: James Bowery The whole point of water-mist EHD systems is that you slow down the charge carriers through an electrostatic field to convert kinetic energy to electrical potential.
