Influence of Magnetic-Field and Plasma-Density Inhomogeneities on the Propagation and Amplification of Radio Waves in the Solar Corona

We analyze the maser generation of millisecond spikes of the solar radio emission at the cyclotron resonance of a fast extraordinary wave in an inhomogeneous medium. It is shown that the magnetic-field inhomogeneity with parameters typical of the solar corona drastically reduces the time of electromagnetic-wave amplification, which is explained by the fact that these waves leave the resonance region in the wave-vector space. As a result, an unstable electron distribution can be formed. The efficient generation of radiation becomes possible only in such local regions where the influence of the magnetic-field inhomogeneity is compensated by small-scale inhomogeneities of the plasma density with typical scales ranging from tens to hundreds of kilometers. Taking the effect of inhomogeneous medium into account allows us to explain spatial and temporal characteristics of the spikes.