Novel High power sources for the physics of Ionospheric Modification

The ionosphere plays a controlling role in the performance of critical civilian and DoD systems including the ELF-ULF communications, radars, navigation (including GPS) and geo-location systems. Ionospheric Modification (IM) is a complementary approach to passively studying the ionosphere that has intensified over the last 30 years with the construction of the High-Frequency Active Auroral Research Program (HAARP). The objective of IM is to control and exploit triggered ionospheric and magnetospheric processes to improve the performance of trans-ionospheric Command, Control, Communications and Intelligence (C3I) systems and to develop new applications that take advantage of the ionosphere as an active plasma medium. A key instrument in IM is the Ionospheric Heater (IH), a powerful High Frequency transmitter that modifies the properties of the ionospheric plasma by modulating the electron temperature at preselected altitudes. A major reason for the development of a Mobile IH source (MIHs) is that it would allow investigators to conduct the needed research at different latitudes without building permanent installations. As part of a multiuniversity research initiative (MURI), UMD will develop a powerful RF source utilizing Inductive Output Tube (IOT) technology running in class-D amplifier mode. This technology was chosen because it has the potential to operate at high efficiencies. Some of the technical challenges presented in this paper will include: a gun design that minimizes intercepted current, a compact tunable hybrid cavity operating in the 1-10 MHz range, and an efficient modulator system capable of modulating a high power electron beam.