ANALOGIES BETWEEN THE FREE-ELECTRON LASER AND WHISTLER-MODE AMPLIFICATION IN THE IONOSPHERE

Very low frequency (VLF) electromagnetic waves, called ''whistler wave s'', propagating along magnetic field lines in the magnetosphere can b e amplified by energetic electrons spiraling around the field lines ne ar the geomagnetic equator. The electron and whistler wave interaction can be described by a theoretical model much like that used for the f ree electron laser (FEL). The electron phase-space dynamics for both i nteractions is governed by the pendulum equation describing saturation , electron trapping, tapering and sensitivity to energy distributions.