Novel high-power radio-frequency sources for mobile ionospheric heating

The ionosphere plays an important role in the performance of critical civilian and defense communication systems. Perturbation studies of the ionosphere allow us to investigate the ionosphere and improve the performance of communications that rely on the ionosphere as well as develop new applications. A key instrument in ionospheric modification is the ionospheric heater, a powerful high frequency transmitter that perturbs the properties of the ionospheric plasma by modulating the electron temperature at preselected altitudes. The latest technology uses stationary facilities, among which HAARP is the largest. There are numerous benefits from using mobile ionospheric heaters (MIHs). Such a mobile system would allow investigators to conduct the research at different latitudes without building a costly permanent installation. These mobile sources would be substantially smaller than HAARP and located on a barge-size platform. A mobile heater for ionospheric modification studies requires a new megawatt class of RF (3-10 MHz) source operating with an antenna that is roughly 1/100 in area of a HAARP antenna [2]. In order to deliver to the ionosphere, an effective power density comparable to that of HAARP, the total source power must be in the range of up to 100 MW, placing a premium on efficiency. The present paper describes some of the technical advances in the development of such sources (inductive output tubes, IOTs): a novel electron gun, which allows the D-class operation of a MW-level IOT without interception of an electron beam by grid electrodes, a prototyping test-stand, two types of modulators capable of driving the mod-anode of a MW level gun and a tunable constant impedance cavity operating in the desired frequency range.