The electron cyclotron maser in hot thermal plasmas

We investigate the possibility of an electron cyclotron maser operating in a hot (T > 107K) thermal plasma with a loss cone. We find that the instability can occur in this scenario because resonance involving electrons in the thermal tail can give rise to significantly large growth rates. We estimate the range of electron velocities that can be in resonance and show how this dictates the frequency and angular distribution of the emitted radiation. In so doing, we show quite generally that it is the range of speeds and not the details of the loss cone edge, as previously thought, that determines the frequency and angular distribution. By considering the energetic constraints on the initial and final (i.e. when the maser is saturated) electron distributions, we estimate bounds on the energy that may be emitted. This energy can be a sizeable fraction (up to 5-10%) of the plasma electrons’ total thermal energy, though this is sensitively dependent on the temperature, density and magnetic field. Finally, we discuss the implications of this emission for flaring solar coronal loops and hot stellar atmospheres.