The basic theoretical support goes back to Maxwell’s theories of electro-magnetism. A charged particle moving through a coil of wire will induce an electric current, loosing some of its kinetic energy. Such a device is basically a particle accelerator operating in reverse. Perhaps the statement of 90% efficiency is based on the performance of such accelerators, which are highly refined instruments. It may be that the hard data is lacking yet because such an abundant and tightly colimated stream of alpha particles traveling at such a high velocity has been a rare item. As an electrician, I am confident that to develop this part of a future FF generator would present surmountable technical problems.
