THOMSON SCATTER MEASUREMENTS OF MAGNETIC FIELD EFFECTS ON LANDAU DAMPING AND EXCITATION OF PLASMA WAVES

Radar observations of Thomson scatter from the nonthermal, steady-state level of plasma waves in the ionosphere are used to test the predictions of kinetic theory with regard to how the nonthermal level of the waves depends on the angle between the wavevector and the magnetic field. Nonthermal effects are produced by a high-energy, photoelectron tail on the otherwise Maxwellian electron velocity distribution. Observations were made at several angles varying from nearly parallel to nearly perpendicular (where cyclotron resonance effects play a major role) to the magnetic field. The results are in consistent agreement with kinetic theory.