Generation mechanism of magnetic noise bursts in the earth's magnetotail

In this paper, we study the electromagnetic instability driven by ion beams and plasma inhomogeneity in the plasma sheet boundary layer and for the first time obtain the growth rate spectrum of electromagnetic waves in a broad frequency range (Q_i ≪ 0. 1ω_LH ≲ |Ω_r| ≤ Q_e, Q_i and Q_e, are respectively the ion and electron cyclotron frequencies, ω_LH = (Q_iQe) ^{1 2} is the lower hybrid frequency). The peak of the growth rate spectrum is near |ω_r| ≈ ω_lH and the second peak is near |ω_r| ≲ Q_e. The fundamental characteristics of the growth rate spectrum are in agreement with the satellite observations of the magnetic noise bursts in the magnetotail.