In-situ observations of VLF waves generated by a modulated electron beam in the ionosphere

Electromagnetic signatures of a medium-power, modulated electron beam were observed by a free-flying wave detector payload during the CHARGE-2B sounding rocket mission. Six-component wave data from the detector are used to calculate the spectrum and Poynting flux, and to explore the electromagnetic character of the observed waves. Strong harmonics of the beam modulation frequency are observed despite a spectrally pure beam current waveform. Total power radiated at the beam modulation frequency is estimated to be generally on the order of 0.1 watt, and is greatest for parallel beam injection, and for modulation near the lower hybrid frequency.