An excitation mechanism for discrete chorus elements in the magnetosphere

Abstract

Abstract. A beam pulsed amplifier mechanism responsible for effective amplification of short very low frequency (VLF) electromagnetic pulses is proposed. Effective amplification near the magnetic equator outside the plasmasphere is considered. A conditional growth rate of short electromagnetic pulses is calculated. Obtained results can explain some important features of the oblique electromagnetic chorus emissions without hiss-like radiation background.

Excitation of chorus with small wave normal angles due to BPA mechanism into density ducts

“…3 Special features of implementation of the BPA mechanism of the chorus excitation in a duct with refractive reflection Now we briefly recall the process of chorus frequency-time spectrogram formation in the implementation of the beam pulse amplifier mechanism (Bespalov and Savina, 2018). At the input of the wave-particle interaction region (z = 0), there is weak noisy emission with an electric field containing a random sequence of weak shot electromagnetic pulses.…”

“…In a homogeneous plasma with beam (8), the electromagnetic pulse increases with growth rate (Bespalov and Savina, 2018)…”

“…We can use a formula for growth rate (9) since the wave modes in the duct conform to the WKB approximation, and therefore their polarization corresponds to the whistler waves in which during the inclined propagation there is a longitudinal component of the wave electric field which is taken into account in the growth rate calculation (Bespalov and Savina, 2018). We will refine now the value of the average angleθ, which should be substituted into formula (9).…”

“…Moreover, it is noted in (Zhou et al, 2015), on the basis of the analysis of a large volume of experimental data, that chorus are frequently excited in the regions of the daytime magnetosphere with a marginal stable plasma without significant anisotropy of the distribution function. For explaining these results, one can use the beam pulse amplifier mechanism (BPA) of chorus excitation not requiring significant anisotropy of the distribution function of energetic electrons in the magnetosphere (Bespalov and Savina, 2018). In a homogeneous plasma, the BPA mechanism is most effective at wave normal angles close to…”