低エネルギー電子ビーム放出による波動 : 粒子相互作用ロケット実験の解析

概要

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In the K-9M-41 rocket experiment performed on January 17, 1973, VLF plasma waves were observed in association with the ejection of an electron beam of energy - 3eV. An electron beam of several tens of μA was emitted from a hot cathode through a potential sink of the rocket body, when a positive DC bias was applied to a receiving dipole antenna in order to increase the efficiency of the antenna by removing an ion sheath around the antenna. The VLF noise has a frequency spectrum resembling the shape of the letter "U" which appeared twice per spin period of the rocket. The emission frequency is always lower than the local LHR frequency, and the minimum frequency of each U spectrum decreases with increasing energy of the electron beam. The frequency of each U shape, which varies synchronously with the rocket spinning, is found to decrease with increasing energy component of the beam in the direction of the geomagnetic field. With regard to the generation mechanism, the ion acoustic or ion cyclotron harmonic modes generally have a phase velocity too slow for the interaction, and the electromagnetic (modified Alfven) mode which propagates along the geomagnetic field line, has no dispersion which prevents it from interacting with the beam. For the electromagnetic mode propagating almost perpendicular to the geomagnetic field, there is a possibility of interacting with the low energy electron beam.
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