Observations of Pitch Angle Changes of Electrons and High‐Frequency Wave Activities in the Magnetotail Plasma Bubble

Abstract

AbstractPlasma bubble, a low‐entropy flux tube, is usually regarded as the bearer of plasma flux transport in the magnetotail. In this study, we perform a complete analysis of electron dynamics in a plasma bubble in the Earth's magnetotail based on the high time‐resolution data from the Magnetospheric Multiscale (MMS) mission. An electron jet is observed at the center of this plasma bubble. Simultaneously, intense electric field and significant current density, as well as the strong energy dissipation are detected associated with this electron jet. The pitch angle distributions (PADs) of high‐energy electrons exhibit different features at different substructures in this plasma bubble. In Region‐1 and Region‐3, pancake‐type PAD is formed; the PAD becomes isotropic type in Region‐2. The electrons pitch angle changes to field‐aligned distribution in Region‐4. All these changes of electron PADs in substructures can be interpreted mainly by the capture of magnetic mirror and betatron cooling. High‐frequency waves, including whistler waves and electrostatic waves, are detected in several parts of the plasma bubble. The observations of abundant electron‐scale phenomena or processes reveal that the electrons are very dynamic in the large‐scale plasma bubble.