NEW ASPECTS OF WHISTLER WAVES DRIVEN BY AN ELECTRON-BEAM STUDIED BY A3-D ELECTROMAGNETIC CODE

We have restudied electron beam driven whistler waves with a 3-D elect romagnetic particle code. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observ ed in the Spacelab 2 electron beam experiment. It has been suggested i n the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simu lation results indicate several inconsistencies with this picture: (1) whistler waves continue to be generated even after the beam mode spac e charge modulation looses its coherence, (2) the parallel (to the bac kground magnetic field) wavelength of the whistler wave is longer than that of the beam instability, and (3) the parallel phase velocity of the whistler wave is smaller than that of the beam mode. The complex s tructure of the whistler waves in the vicinity of the beam suggest tha t the transverse motion (gyration) of the beam and background electron s is also involved in the generation of whistler waves.