Electron cyclotron maser instability in space plasmas with kappa loss-cone distribution

Abstract

It is well known that non-thermal electrons, often modeled by the kappa distribution, are ubiquitously observed in space. Kappa-type distributions have been widely discussed in various plasma environments. On the other hand, when these non-thermal electrons are trapped by magnetic fields in space they frequently have a loss-cone distribution in velocity space. In this paper, we investigated the growth rates of electron cyclotron maser (ECM) instability in space plasmas by using a kappa loss-cone distribution. Based on the cold plasma assumption and weakly relativistic approximation, the results show that non-thermal electrons with such a distribution can excite ECM emission efficiently. The growth rates of O1 and X2 modes both increase with the kappa spectral index (κ) but the growth rate of X2 mode increases slightly more rapidly than that of O1 mode. The present analysis also shows that the growth rates increase rapidly with the loss-cone index σ for σ < 10 but increase comparatively slowly for larger σ values. © 2012. The American Astronomical Society. All rights reserved.