Interrelation between azimuthal bunching and semirelativistic maser cyclotron instabilities

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Abstract
A theory is presented for electron-cyclotron instabilities driven by an anisotropic electron velocity distribution. The growth rates of the azimuthal bunching and semirelativistic maser cyclotron instabilities are calculated for a plasma consisting of an arbitrary ratio of cold and suprathermal electrons. It is found that both types of instabilities can be present in the same plasma and that they are different limiting cases of the same instability. The growth rate of the azimuthal bunching instability is smaller than previous estimates because of the spread in electron velocities. The analysis is relevant in explaining Jupiter's decametric radio emission and terrestrial kilometric radiation and in the theory of the gyrotron.
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