Highly efficient, megawatt-class, radio frequency source for mobile ionospheric heaters

A mobile heater for ionospheric modification studies requires a new megawatt (MW) class radio frequency (RF) source operating with an antenna array 1/20 the area of the High-Frequency Active Auroral Research Program (HAARP). To deliver an effective power density comparable to HAARP, the total source power must be in the range of 16 MW, thus demanding highly efficient sources. While the development of a whole multi-megawatt system for mobile ionospheric heaters is a complex engineering problem, in the present paper we describe only the work of our group on studying main features of a prototype MW-class vacuum electronics RF source for such system. The source design we are currently pursuing assumes class D operation using a modified version of the inductive output tube. The electron beam is a thin annular beam, switched on and off by a mod-anode as opposed to a grid. The beam is then passed through a decelerating gap, and its kinetic energy is extracted using a tunable resonant circuit that presents a constant impedance in the range of 3–10 MHz. With this design the beam is almost completely decelerated at all frequencies, thus achieving high efficiency.