VLF plasma wave excitation due to low‐energy electron beam injection: Laboratory simulation of a rocket experiment

Abstract

A laboratory simulation experiment of low‐energy electron beam injection into the ionosphere is performed. Two kinds of waves are excited in VLF frequency range. One with a lower frequency is shown to be caused by an interaction between the beam with a finite cross section and a background plasma. The other with a higher frequency is shown to be caused by a current‐driven ion turbulence due to an electron return current. These two kinds of VLF waves have been observed before in Japanese rocket experiments in the ionosphere. A retarding potential analyzer measurement revealed that the injected beam has a diameter twice as large as the cyclotron radius of beaming electrons. It is shown that the field intensity of the excited VLF waves drops off outside the measured beam column. A correlation measurement of the phase of the VLF wave shows that the phase velocity of the wave excited by the beam instability is equal to that of ion acoustic waves. A dispersion and wave vector measurement has shown that the current‐driven ion turbulence is an ion cyclotron wave whose phase velocity is of the order of the ion acoustic wave velocity Cs.