Особенности возбуждения хоров посредством BPA механизма в магнитосферных волноводах уплотнения и разрежения с рефракционным отражением
Features of the implementation of a beam-pulse amplifier (BPA) of whistler waves in magnetospheriс enhanced and depleted ducts with refraction reflection are considered. Extended along the magnetic field, ducts with a width of about 100–300 km often occur after magnetic disturbances in the morning and daytime magnetospheres beyond the plasmapause, where the excitation of chorus emissions occurs under the same conditions. The dispersion characteristics of whistler emissions in a planar duct are analyzed under the conditions of the Wentzel–Kramers–Brillouin (WKB) approximation and refractive reflection from the “walls.” For enhanced (depleted) ducts, it is shown that, for the first ten modes at frequencies below (above) half of the electron-cyclotron frequency, the conditions for exciting discrete spectral elements with wave normal angles to the magnetic field less than 20° can be satisfied. The magnitude of the amplification of noise pulses with the indicated angles of the wave normal is only 20% less than in homogeneous plasma at an optimal angle of about 39°. The proposed model explains the possibility of excitation of chorus emissions with relatively small angles of the wave normal by means of the BPA mechanism. It was found that both the intensities and the typical angles of the wave normal can differ significantly in the lower and upper bands of excitation of the choruses.