Excitation of chorus with small wave normal angles due to beam pulse amplifier (BPA) mechanism in density ducts

摘要: Abstract. We examine specific features of the realisation beam pulse amplifier (BPA) mechanism chorus excitation in density ducts that have a width order 100–300 km with refractive reflection. The dispersion characteristics whistler emissions planar duct under conditions for fulfilment Wentzel–Kramers–Brillouin (WKB) approximation and reflection from “walls” are analysed. It is shown enhanced duct, discrete spectral elements narrow angular spectrum along external magnetic field can be excited at frequencies somewhat lower than half electron cyclotron frequency. In depleted higher frequency, excited. proposed model explains possibility small angles wave normal when BPA implemented. noted properties chorus, such as intensity typical angle normal, different lower- upper-band chorus.