Wave-particle interactions produced by a low-energy electron beam injected into the ionosphere are experimentally examined in a space simulation plasma chamber. The energy range of the beam is from thermal (∼0.1 eV) to 4 eV. An electrostatic VLF wave with a monochromatic frequency well below the LHR frequency is excited. The beam-excited wave propagates almost perpendicular to the beam flow direction. The phase velocity of the excited wave is much slower than the ion sound speed in the background plasma. A standing wave is observed within a hollow region surrounded by a conic beam in the direction perpendicular to the conic axis, but the wave inside the hollow cone is found to propagate along the conic axis. The frequency changes of the emissions observed in the previous rocket experiment are successfully reproduced when the beam injection angle from the magnetic field is changed.
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