A significant amount of the energy released by fusion reactions is composed of electromagnetic radiation, essentially X-rays due to Bremsstrahlung. Those X-rays can not be converted into electric power with the various electrostatic and magnetic direct energy converters listed above, and their energy is lost.
Whereas more classical thermal conversion has been considered with the use of a radiation/boiler/energy exchanger where the X-ray energy is absorbed by a working fluid at temperatures of several thousand degrees, more recent research done by companies developing nuclear aneutronic fusion reactors, like Lawrenceville Plasma Physics (LPP) with the Dense Plasma Focus, and Tri Alpha Energy, Inc. with the Colliding Beam Fusion Reactor (CBFR), plan to harness the photoelectric and Auger effects to recover energy carried by X-rays and other high-energy photons. Those photoelectric converters are composed of X-ray absorber and electron collector sheets nested concentrically in an onion-like array. Indeed, since X-rays can go through far greater thickness of material than electrons can, many layers are needed to absorb most of the X-rays. LPP announces an overall efficiency of 81% for the photoelectric conversion scheme.