Theory of beat wave excitation in an inhomogeneous plasma

The theory of beat wave excitation in a slightly inhomogeneous plasma is pr esented. While the theory is general it applies directly to the experiments performed in Alaska by the ionospheric heating facilities HIPAS [High Powe r Auroral Simulation, Radio Sci. 25, 1269 (1990)] and HAARP [High Frequency Active Auroral Research Project, Geophys. Res. Lett. 25, 257 (1998)]. A ra y tracing (WKB) formalism appropriate for computations is developed. The co mputational implementation of this formalism and extensive results will be presented in a follow up to this paper. Also the beat wave excitation of up per-hybrid waves is investigated analytically. The complicated trajectories of these waves in the plasma are described. When this beat wave reaches th e plasma wave resonance it can, in the HIPAS-HAARP experiments, attain nonl inear amplitude. The electrostatic upper-hybrid waves are trapped around th e density maximum of the ionosphere. This trapping is investigated in detai l. Beat wave pumping of the trapped modes is possible using HAARP and HIPAS or with split beams from HAARP. (C) 2001 American Institute of Physics. [D OI: 10.1063/1.1329149].