INTERACTION OF A DENSITY MODULATED ELECTRON-BEAM WITH A MAGNETIZED PLASMA - EMISSION OF WHISTLER WAVES

Whistler wave excitation in a magnetized laboratory plasma by a densit y modulated electron beam is studied for frequency modulation below, b ut in the range of, the electron gyrofrequency. When the beam velocity differs from the phase velocity of the whistler at the frequency modu lation of the beam, a whistler wave, and, by Cerenkov emission, a beam wave at the same frequency are excited as single poles. When both vel ocities are equal, a resonance occurs leading to a maximum in the emis sion of whistler waves. The experiment performed in a magnetized plasm a (n(p) almost-equal-to 10(11) cm-3, T(e) almost-equal-to 0.2 eV, B al most-equal-to 100 G) with a modulated electron beam (n(b) almost-equal -to 10(9) cm-3 , E(b) almost-equal-to 300 eV) is in agreement with a s imple model which predicts the characteristics of the excited waves.