A Parametric Investigation on the Cyclotron Maser Instability Driven by Ring-beam Electrons with Intrinsic Alfv\'en Waves

摘要

The electron-cyclotron maser is a process that generates intense and coherentradio emission in plasma. In this paper, we present a comprehensive parametricinvestigation on the electron-cyclotron-maser instability driven by non-thermalring-beam electrons with intrinsic Alfv\'en waves which pervade the solaratmosphere and interplanetary space. It is found that both forward propagatingand backward propagating waves can be excited in the fast ordinary (O) andextraordinary (X) electromagnetic modes. The growth rates of X1 mode are almostalways weakened by Alfv\'en waves. The average pitch-angle $\phi_0$ ofelectrons is a key parameter for the effect of Alfv\'en waves on the growthrate of modes O1, O2 and X2. For a beam-dominated electron distribution($\phi_0 \lesssim 30^\circ$ ), the growth rates of the maser instability forO1, O2 and X2 modes are enhanced with the increase of Alfv\'en wave energydensity. In other conditions, the growth rates of O1, O2 and X2 modes weakenedwith increasing Alfv\'en wave intensity, except that the growth of O1 mode mayalso be enhanced by Alfv\'en waves for a ring distribution. The results may beimportant for us in analyzing the mechanism of radio bursts with various finestructures observed in space and astrophysical plasmas.